HomeMy WebLinkAboutStaff Report 7633
City of Palo Alto (ID # 7633)
City Council Staff Report
Report Type: Action Items Meeting Date: 3/7/2017
City of Palo Alto Page 1
Summary Title: Direct Staff to Take Further Action to Minimize Basement
Construction Pumping of Groundwater
Title: Adoption of an Ordinance Amending Chapter 16.28 of the Municipal
Code to Require Testing, Monitoring and Protective Measures for Temporary
Construction-Related Dewatering and Consideration of Recommendations
From Policy and Services Committee to Direct Staff to Analyze Additional
Measures to Minimize Construction-Related Groundwater Pumping
From: City Manager
Lead Department: Public Works
Recommendation
At their December 14, 2016 meeting, the Policy and Services Committee
recommended that Council:
1. Adopt seven new components for the City’s Construction Dewatering
Guidelines. Staff is further recommending that Council adopt an ordinance
codifying the Dewatering Guidelines, with the updates recommended by
Policy and Services, in the Municipal Code at Chapter 16.28 (Attachment A).
2. Direct staff to consider four additional requirements and return to Council
for adoption, with a goal of making the new requirements applicable for
the 2018 construction season (Attachment B).
Executive Summary
Policy and Services Committee endorsed staff recommendations being forwarded
to Council regarding the Construction Dewatering Program approved by Council in
February 2016 including enhancements occurring in two phases; the first applied
to the 2017 construction season and the second to 2018.
City of Palo Alto Page 2
The 2017 enhancements would include improving fill station performance,
ensuring watering of adjacent neighboring vegetation, monitoring actual
groundwater elevation changes, clarifying reporting, and enhancing the
Hydrogeological Study, while adding an exemption to the Study if cut-off wall
technology is used to limit groundwater pumping. Staff recommends the current
program with proposed 2017 additions be implemented, and that the attached
ordinance (Attachment A) be adopted.
The second phase would potentially contain additional enhancements, subject to
further analysis. Staff will return to Council to authorize these enhancements,
with a goal of making them applicable for the 2018 construction season
(Attachment B).
Staff recommended two additional requirements for 2018 that the Policy and
Services Committee did not recommend that Council pursue. These are
development of an additional pumping fee and a requirement to analyze the
impacts of multiple pumping sites operating at once.
Of the four new requirements being recommended to Council for further
evaluation, the most impactful is cut-off walls (or similar advanced technologies)
be considered as a requirement in 2018 and a maximum of 30 gallons per minute
(gpm) as a performance standard.
Background
Council approved construction groundwater pumping requirements in February
2016 for the 2016 construction season (Attachment A: CMR 6478). The
requirements apply to sites not having either their Conditions of Approval from
the Planning Department, or their building permit from Development Services by
February 16, 2016. These requirements were incorporated into the planning and
building permit process on a pilot basis for the 2016 construction season. Staff
was to evaluate the results of the pilot and return to Council with a proposed
ordinance codifying specific requirements.
At the same time, Council directed staff to continue working with Santa Clara
Valley Water District to further understand the North County groundwater
systems and provide an update. That update was provided in April 2016
(Attachment C: CMR 6700).
City of Palo Alto Page 3
Discussion
In reviewing the results and experiences of the 2016 pilot, staff found:
1. There were eight residential basement construction sites which required
pumping to the storm drain system. The total water pumped from all sites
was 140 million gallons (MG). As a point of comparison, the City of Palo Alto
uses about 8 MG per day. The City required that pumping be completed in
10 weeks and not extend beyond October 31. The average duration of
pumping was 10.8 weeks. Based on this data and discussions with
stakeholders, it appears the 10-week time frame is more generally
achievable if a two week start-up period is added ahead of the 10-week
period.
2. Three of the sites were required to submit a Geotechnical Study and draw
conclusions about potential impacts. The other sites received their
Conditions of Approval or building permits before February 16, 2016, and
did not have to perform this study. Generally, the studies that were done
predicted lower flow rates than occurred. The calculations were not well
supported and readily verifiable. Community members submitted
comments and observations suggesting the very low groundwater
drawdown levels predicted may have been substantially exceeded.
3. Some neighbors and truckers complained water flow rates from the fill
stations were inadequate. This can be remedied by requiring performance
tests prior to full start-up and storage tanks being configured so they are
always at least one-half full.
4. Recorded flow monitoring was spotty and prone to error. The City’s
reporting requirements need to be strengthened and include accuracy
checks for meters.
5. Some of the flow meters were placed without sufficient attention to safety,
and safety measures need improvement.
Based on analysis of the pilot results, input from stakeholders and previous
direction from Council, staff is recommending modifications to the dewatering
City of Palo Alto Page 4
requirements in two phases. The first phase is making relatively minor changes to
the requirements adopted by Council for the 2016 construction season. Proposed
changes 1 through 3 below (and the pre-existing requirements) would apply to all
sites in the 2017 construction season. Proposed changes 4 through 7 would apply
to those sites not having a building permit or Planning Conditions of Approval
before the effective date of the attached ordinance. The second phase would be
implemented after further analysis and return to Council, with a goal of being
effective the 2018 construction season. The two phases are described below:
First Phase: Proposed changes for the 2017 Construction Season
1. Fill Stations: Demonstrate a maximum 10-minute truck fill time and 2
simultaneous, 100’ hose, 10 gallons per minute (gpm) deliveries (for each
hose) during the two week start up period defined below. Design the tank
system so that the storage tank is always at least one-half full. Ongoing
metering of instantaneous and total flow of fill stations is currently
required.
2. Pump for no more than 10 weeks for residential sites. A two week start-up
period ahead of the 10 weeks is allowed. At the end of the two week start-
up period, compliance with all performance standards and water quality
standards shall be demonstrated.
3. Report on all measurements and requirements (reports due at the end of
the two-week start-up period, then bi-weekly, and then a final report at the
end of pumping).
4. At the basement slab center, pump the groundwater down no deeper than
3 feet below the depth of the slab, following the two week start-up period.
Once the slab is poured, the depth to the center of the slab shall be 1 foot.
5. Offer to water trees/plants on adjacent properties and do so if requested.
6. The City will add supplemental city contract resources to manage
information, review submittals, verify compliance and prepare public
reports; and add those costs to city permit fees (this will average to
approximately $10,000 per site).
City of Palo Alto Page 5
7. Geotechnical Study Enhancements
a) Currently a Geotechnical Study is required to determine groundwater
drawdown levels and any associated impacts. The key change for CY
2017 is to require verification of the anticipated drawdown curve with a
pump test using actual wells, by the end of the two week start-up
period. Cone Penetrometer Tests (CPT) is also encouraged to verify soils
data. The actual pumping rates, following the two week start-up period,
shall be limited to the rates used in in the verification. The maximum
amount of water pumped over the 10-week period, (excluding the 2
week start- up period) shall be limited to that calculated during
verification. This activity will add on the order of $10,000 to the
construction cost of a basement (separate from the additional $10,000
permit fee described in #6 above).
b) To support the work in (a) above, measure the ground water level at a
distance representative of the distance to the nearest structure on an
adjacent parcel, or farthest feasible point on the subject site. This
monitoring shall be daily for the first week (including the two week
start-up period), then weekly thereafter. If drawdown results are
greater than anticipated by the Geotechnical Study, at the end of the 2
week start-up period or thereafter, submit a revised Geotechnical Study
and any revised conclusions on impacts of the groundwater drawdown.
The cost of this activity is largely covered by the cost of (a) above, but
some additional cost will be incurred.
c) Survey and mark land elevations on structures on adjacent parcels
(assuming permission is obtained) prior to any pumping. This activity will
not add significantly to construction costs, as survey measurements are
routinely taken.
d) The Geotechnical Study and verification shall not be required if the
storm drain pumping is continuously limited to 30 gallons per minute
(gpm) following the two week start-up period. This could be
accomplished through installation of groundwater cut-off walls (such as
secant walls) or similar construction techniques. (These optional
activities would, if implemented, add significantly to the cost of
constructing basements.) Similarly, the 10 week pumping period can be
extended if the 30 gpm flow rate is continuously achieved following the
two-week start-up period. The fee described in item 6, would also be
lowered dramatically or eliminated. Additionally, the contractor need
City of Palo Alto Page 6
only provide off-site hauling of water sufficient to meet the needs of
adjacent neighbors, as opposed to the one-day per week requirement
for 2016.
Second Phase: Potential Calendar Year (CY) 2018 Construction Season Changes,
for further analysis by staff and return to Council:
1. Determine whether existing wells from other sites/purposes can be used to
satisfy the groundwater monitoring requirements; utilize such existing wells
if practical.
2. Limit the groundwater level drawdown at the closest off-site adjacent
structure to 3’.
3. Determine whether existing wells can be used to satisfy the requirement in
(b) above; if not, install a new monitoring well.
4. Potentially, require the use of groundwater cut-off walls, or other
construction methods, which will limit the pumping (following a two week
start-up period) to 30 gallons per minute (gpm).
Resource Impact
The City’s review, monitoring, and approvals associated with program
implementation of the suggested measures will require approximately $100,000
in contract services. If this approach is approved, Council will be asked to approve
a budget amendment in the General Fund as well as an amendment to the
Municipal Fee schedule to allow cost- recovery. If the 2017 changes are approved,
staff estimates the cost of basement construction would increase by
approximately $20,000 per site.
Environmental Review
The 2017 recommended program enhancements are minor modifications to an
existing regulatory program designed to be protective of the environment. These
modifications are not subject to the California Environmental Quality Act (CEQA)
as there is no possibility the modifications may have a significant effect on the
environment (CEQA Guidelines Section 15061(b)(3)).
The potential 2018 requirements will be evaluated and the appropriate
environmental review prepared as specific proposals are developed.
City of Palo Alto Page 7
Attachment A: 2017 Ordinance amending the Municipal Code by adding
Amending Chapter 16.28
Attachment B: List of Additional Potential Requirements to be considered by Staff
for 2018
Attachment C: February 1, 2016 CMR 6478
Attachment D: 2016 Pumping Requirements
Attachment E: April 11, 2016 CMR 6700
Attachments:
Attachment A: Dewatering ORD Chapter 16.28 v2
Attachment B: Second Phase Potential Calendar CY2018
Attachment C: SR 6478 Approval of 2016 Basement Construction Dewatering Program
Changes
Attachment D: Guidelines for Dewatering During Below Ground Construction
Attachment E: SR 6700 Update on Recycled Water Planning Efforts and Groundwater
Studies
Attachment F - Council letter 03-07-17 - Dewatering1
Attachment G - Council letter 03-07-17 - Dewatering2
NOT YET APPROVED
1 February 2, 2017
Ordinance No. ____
Ordinance of the Council of the City of Palo Alto Amending Chapter 16.28 of the
Municipal Code to Require Testing, Monitoring and Protective Measures for
Temporary Construction-Related Groundwater Pumping (Dewatering)
The Council of the City of Palo Alto does ORDAIN as follows:
SECTION 1. Findings and Declarations. The City Council finds and declares as follows:
A. Temporary pumping and discharge of groundwater during construction of below-
ground basements and garages removes tens of millions of gallons of groundwater in Palo Alto
each year, and discharges this water to the storm drain system.
B. For many years, Palo Alto has prohibited pumping of groundwater after the
completion of basement construction.
C. In recent years, concerns have arisen regarding dewatering and its impacts, including
significant waste of a community resource, potential damage to neighboring structures, trees
and vegetation, and possible impacts on the groundwater system.
D. To begin to address these concerns and gather additional information for potential
future action, the Palo Alto City Council adopts this ordinance requiring testing, monitoring and
protective measures where temporary construction-related groundwater pumping
(dewatering) will occur.
SECTION 2. Section 16.28.030 of Chapter 16.28 (Grading and Erosion and Sediment
Control) of the Palo Alto Municipal Code is hereby amended to read as follows:
16.28.030 Definitions.
When used in this chapter, the following words shall have the meanings ascribed to
them in this section.
(a) "Applicant" means any person, corporation, partnership, association of any type,
public agency, or any other legal entity who submits an application to the building official for a
permit pursuant to this chapter.
(b) "As-graded" means the surface conditions extant on completion of grading.
(c) "Bedrock" means in-place solid rock.
(d) "Bench" means a relatively level step excavated into earth material on which fill is
to be placed.
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(e) "Best management practices" means a technique or series of techniques which,
when used in an erosion control plan, is proven to be effective in controlling construction-
related runoff, erosion, and sedimentation.
(f) "Borrow" means earth material acquired from an off-site location for use in grading
on a site.
(g) "Building official" means the chief building official of the city of Palo Alto and
his/her duly authorized designees.
(h) "City engineer" means the city engineer of the city of Palo Alto and his/her duly
authorized designees.
(i) "Civil engineer" means a professional engineer registered in the state of California to
practice in the field of civil works.
(j) "Civil engineering" means the application of the knowledge of the forces of nature,
principles of mechanics, and the properties of materials to the evaluation, design, and
construction of civil works for the beneficial uses of mankind.
(k) "Compaction" means the densification of a fill by mechanical means.
(l) "Drainageway" means a natural or manmade channel which collects and
intermittently or continuously conveys storm water runoff.
(m) "Earth material" means any rock, natural soil, or fill, and/or combination thereof.
(n) "Engineering geologist" means a geologist experienced and knowledgeable in
engineering geology and certified by the state of California to practice engineering geology.
(o) "Engineering geology" means the application of geologic knowledge and principles
in the investigation and evaluation of naturally occurring rock and soil for use in the design of
civil works.
(p) "Erosion" means the wearing away of the ground surface as a result of the
movement of wind, water, and/or ice.
(q) "Final erosion and sediment control and storm water pollution prevention plan
('final plan')" means a set of best management practices or equivalent measures designed to
control surface runoff and erosion and to retain sediment on a particular site after all other
planned final structures and permanent improvements have been erected or installed.
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(r) "Grade" means the vertical location of the ground surface. "Existing grade" means
the grade prior to grading. "Rough grade" means the stage at which the grade approximately
conforms to the approved plan. "Finish grade" means the final grade of the site which conforms
to the approved plan.
(s) "Grading" means any land disturbance or land fill, or combination thereof.
(t) "Interim erosion and sediment control and storm water pollution prevention plan
('interim plan')" means a set of best management practices or equivalent measures designed to
control surface runoff and erosion and to retain sediment on a particular site during the period
in which pre-construction and construction-related land disturbances, fills, and soil storage
occur, and before final improvements are completed.
(u) "Key" means a designed compacted fill placed in a trench excavated in earth
material beneath the toe of a proposed fill slope.
(v) "Land disturbance" or "land-disturbing activities" means any moving or removing by
manual or mechanical means of the soil mantle or top six inches (6") of soil, whichever is
shallower, including but not limited to excavations.
(w) "Land fill" means any human activity depositing soil or other earth materials.
(x) "Manual of standards" means a compilation of technical standards and design
specifications published by the Association of Bay Area Governments.
(y) "Permittee" means the applicant in whose name a valid permit is duly issued
pursuant to this chapter and his/her agents, employees, and others acting under his/her
direction.
(z) "Sediment" means earth material deposited by water or wind.
(aa) "Site" means any lot or parcel of land, or contiguous combination under the same
ownership where grading is performed or permitted.
(bb) "Slope" means an inclined ground surface, the inclination of which is expressed as
a ratio of horizontal distance to vertical distance.
(cc) "Soil" means naturally occurring superficial deposits overlying bedrock.
(dd) "Soils engineer" means a professional civil engineer experienced and
knowledgeable in the practice of soils engineering and licensed by the state of California for
practice in that field.
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(ee) "Soils engineering" means the application of the principles of soils mechanics in
the investigation, evaluation, and design of civil works involving the use of earth materials and
the inspection and/or testing of the construction thereof.
(ff) “Temporary construction-related dewatering” means temporary pumping of
groundwater to facilitate construction of underground structures such as basements and
garages.
(ffgg) "Wet season" means the period from October 1 to April 15.
SECTION 3. Section 16.28.060 of Chapter 16.28 (Grading and Erosion and Sediment
Control) of the Palo Alto Municipal Code is hereby amended to read as follows:
16.28.060 Permit required.
No person may grade, fill, excavate, store, or dispose of soil and earth materials or
perform any other land-disturbing or land-filling activity, or engage in temporary construction-
related dewatering, without first obtaining a permit as set forth in this chapter, except when
the activity is performed in accordance with one or more of the general or specific exemptions
set forth in Sections 16.28.070 and 16.28.080. Exemption from the requirement to obtain a
permit does not provide relief from the requirement to conduct all grading activities in
conformance with the general grading requirements contained in Sections 16.28.270 through
16.28.340 of this chapter.
SECTION 4. Section 16.28.070 of Chapter 16.28 (Grading and Erosion and Sediment
Control) of the Palo Alto Municipal Code is hereby amended to read as follows:
16.28.070 General exemptions.
All land-disturbing or land-filling activities or soil storage, and all temporary
construction-related dewatering, shall be undertaken in a manner designed to minimize surface
runoff, erosion, and sedimentation and to safeguard life, limb, property, and the public welfare.
A person performing such activities need not apply for a permit pursuant to this chapter, if all
the following criteria are met:
(a) The site upon which land area is to be disturbed or filled is 10,000 square feet or
less, except where temporary construction-related dewatering will be required.
(b) Natural and finished slopes are flatter than 10:1.
(c) Volume of soil or earth materials stored is 100 cubic yards or less.
(d) Rainwater runoff is diverted, either during or after construction, from an area
smaller than 5,000 square feet.
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170203 th 0140175 5 February 2, 2017
(e) An impervious surface, if any, of less than 5,000 square feet is created.
(f) No drainageway is blocked or has its storm water carrying capacities or
characteristics modified.
(g) The activity does not take place within 100 feet by horizontal measurement from
the top of the bank of a watercourse, the mean high watermark (line of vegetation) of a
body of water or the boundary of the wetlands associated with a watercourse or water
body, whichever distance is greater.
SECTION 5. Section 16.28.155 is hereby added to Chapter 16.28 (Grading and Erosion
and Sediment Control) to read as follows:
16.28.155 Additional Requirements for Temporary Construction-Related Dewatering
(a) In addition to applicable requirements in this Chapter 16.28, where temporary
construction-related dewatering will be required, applicants also shall:
(1) Submit a dewatering geotechnical study conforming to regulations issued by the City
Engineer, adhere to its findings, and make modifications as directed by the City Engineer.
(2) Install and maintain at least one fill station meeting standards established by the
City Engineer.
(3) With the consent of neighboring property owners, water trees and other vegetation
on adjacent properties.
(4) Verify the anticipated drawdown curve in the dewatering geotechnical study with a
pump test performed on monitoring wells installed on the project site, as specified by the City
Engineer.
(5) Prior to pumping, survey and mark elevations on structures on adjacent parcels.
(6) Submit periodic measurements and reports as required by the City Engineer.
(7) Continuously comply with all permit conditions, performance measures, regulations
and requirements established by the City Engineer. Promptly implement corrective actions
identified by the City to address any compliance issues.
(b) Prior to pouring a basement slab, groundwater may be pumped no deeper than
three feet below the depth of the slab, measured at the center. After the slab is poured,
groundwater may be pumped no deeper than one foot below the center.
NOT YET APPROVED
170203 th 0140175 6 February 2, 2017
(c) Dewatering may not be conducted before April 1 or after October 31. Pumping
permits for single family residential basements are limited to ten (10) weeks, with an additional
two (2) week start-up period. At the end of the start-up period, the applicant must demonstrate
compliance with all performance and water quality standards established by the City Engineer.
The City Engineer may adopt a regulation specifying time limitations for commercial property
pumping.
(d) The City Engineer is authorized to establish and from time to time revise regulations
to implement this Section and advance the goals of minimizing temporary construction-related
dewatering and reducing its impacts.
(e) Where pumping is continuously limited to no more than 30 gallons per minute, the
City Engineer is authorized to waive requirements for a geotechnical study, verification
procedures and pump time limitations.
SECTION 6. Severability. If any provision, clause, sentence or paragraph of this
ordinance, or the application to any person or circumstances, shall be held invalid, such
invalidity shall not affect the other provisions of this Ordinance which can be given effect
without the invalid provision or application and, to this end, the provisions of this Ordinance
are hereby declared to be severable.
SECTION 7. CEQA. The City Council finds and determines that this Ordinance is not a
project within the meaning of section 15378 of the California Environmental Quality Act
(“CEQA”) because it has no potential for resulting in physical change in the environment, either
directly or ultimately. In the event that this Ordinance is found to be a project under CEQA, it is
subject to the CEQA exemption contained in CEQA Guidelines section 15061(b)(3) because it
can be seen with certainty to have no possibility of a significant effect on the environment in
that this Ordinance simply clarifies existing local regulations.
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SECTION 8. Effective Date. This ordinance shall be effective on the thirty-first date after
the date of its adoption.
INTRODUCED:
PASSED:
AYES:
NOES:
ABSTENTIONS:
ABSENT:
ATTEST: APPROVED:
______________________________ ____________________________
City Clerk Mayor
APPROVED AS TO FORM: ____________________________
City Manager
______________________________
City Attorney ____________________________
Director of Public Works/ City Engineer
Attachment B
Construction Groundwater Pumping
Second Phase: Potential Calendar Year (CY) 2018 Construction Season Changes:
1. Determine whether existing wells from other sites/purposes can be used to
satisfy the groundwater monitoring requirements; utilize such existing wells
if practical.
2. Limit the groundwater level drawdown at the closest off-site adjacent
structure to 3’.
3. Determine whether existing wells can be used to satisfy the requirement in
(c) above; if not, install a new monitoring well.
4. Potentially, require the use of groundwater cut-off walls, or other
construction methods, which will limit the pumping (following a two week
start-up period) to 30 gallons per minute (gpm).
City of Palo Alto (ID # 6478)
City Council Staff Report
Report Type: Action Items Meeting Date: 2/1/2016
City of Palo Alto Page 1
Summary Title: Approval of 2016 Basement Construction Dewatering
Program Changes
Title: Approval of 2016 Basement Construction Dewatering Program Changes
and Other Related Issues
From: City Manager
Lead Department: Public Works
Recommendation
Staff recommends that City Council approve the five “Group 1” basement
construction dewatering program changes for the 2016 construction season listed
below and provide staff direction for returning to the Policy and Services
Committee with updates and discussion of other work items related to
groundwater and basement construction dewatering issues. This is based on a
unanimous recommendation from the Policy and Services Committee to forward
the program changes to the full Council as an action item.
Executive Summary
The Policy and Services Committee discussed staff recommendations on
investigating program enhancements for basement construction dewatering at its
December 1 and 15, 2015 meetings (Attachment A: #6268 and #6450). The
discussion items were organized into three groups: Group 1, a set of potential
new requirements for the 2016 construction season which are being brought to
the Council for approval with a goal of swift implementation; Group 2, ongoing
and potential future work for gathering information about the groundwater basin;
and Group 3, a list of additional (some big) ideas generated at the December 1,
2015 Policy and Services meeting. With respect to Group 3, staff will return to the
Committee in the first half of 2016 with questions that should be considered part
of a further discussion with the Committee about whether to recommend Council
consideration and potential direction on any of these. The potential scope of the
City of Palo Alto Page 2
items could make this a major new initiative and will require careful assessment
of the resources necessary to support them, in the context of other work
priorities.
Staff has further refined the Group 1 items for approval. Staff is keeping new
applicants advised of the concepts under consideration to avoid any surprises at
the end of the permitting process. The Policy and Services Committee
unanimously approved the Group 1 recommendations, but asked that they be an
Action item for full Council, so that they could be discussed.
Background
Over the years, basement construction groundwater pumping has generated
public concern in Palo Alto. The ongoing drought and mandated water restrictions
this past summer escalated those concerns. Public concerns relate to the
apparent wasting of water by discharging to storm drains, potential impacts on
groundwater elevation and flow volume, as well as potential effects on
neighboring properties, such as subsidence and cracks, and effects on trees and
other landscaping.
Basement construction is often required for non-residential, mixed use and
multifamily residential buildings, particularly if underground parking is included in
the proposal. Additionally, the high value of land and housing in Palo Alto
translates into residential property owners seeking to increase their single family
homes by constructing basements. Basements constructed in R-1 districts do not
count towards allowable square footage (regulated by floor area ratio) and can be
quite large when located underneath the entire building footprint (PAMC Section
18.12.090). Basement construction groundwater pumping occurs when a
basement is constructed in areas of shallow groundwater, typically in the
neighborhoods closer to the bay or near former creek beds. Perimeter wells are
established to draw down the groundwater allowing for construction of the
basement. Dewatering continues until enough of the house has been constructed
to keep the basement in place. The City of Palo Alto has long regulated several
aspects of basement groundwater pumping for both residential and commercial
sites (see Attachment A for a detailed discussion). Additional correspondence
received is attached (Attachment C).
Discussion
City of Palo Alto Page 3
At the December 15, 2015 Policy and Services Committee meeting, Committee
members voted unanimously to forward Group 1 items to Council for approval as
soon as possible. Staff has further developed the Group 1 activities and is seeking
approval of the following new requirements:
Group 1: New Basement Dewatering Submittal, Fill Station and Groundwater
Use Requirements
1. Encourage greater fill station use through public outreach and enhanced
signage. This is a contractor requirement and City activity and includes
continuing to use door hangers, Neighborhood Preparedness Coordinators and
the City’s website.
2. City staff to strengthen outreach on the water cycle and value of fresh water
flows to storm drains, creeks and bay.
3. Add additional requirements to Groundwater Use Plans that are already
required for dewatering. These additional requirements include maximizing
on-site water reuse (e.g. watering on-site and nearby vegetation), at least one
day per week water truck hauling service for neighbor and City landscaping,
and piping to nearby parks or major users where feasible.
4. Expand fill station specifications that must be implemented by contractors to
address water pressure issues from multiple concurrent users, including
separate pumps for neighbors where needed and sidewalk bridges for hoses to
reduce tripping hazards. City inspectors will inspect fill stations to ensure
compliance with specifications.
5. Require Grading Permit applicants anticipated to or encountering groundwater
to submit a statement of the effects of the proposed groundwater pumping on
nearby buildings, infrastructure, trees, or landscaping.
Under Section 16.28 of the Palo Alto Municipal Code, the City Engineer is
authorized to require augmentation of the Soils and Geotechnical Reports as
part of the Grading Permit application. The statement of dewatering effects
must be stamped by a California licensed Geotechnical Engineer and
submitted to the City. This report will be made available for public review. The
City of Palo Alto Page 4
Geotechnical Engineer is to be separate from and independent of the project’s
design engineer(s). The detailed requirements are described in Attachment B:
Draft Basement Construction Dewatering Requirements, and in anticipation of
the City Council’s potential action, on January 14th development project
owners/applicants were notified of these pending requirements and advised
to begin assembling the required information.
Staff recommends approval of these new requirements which will be
incorporated into the planning and building permit process on a pilot basis for the
2016 construction season. Pending further experience with dewatering
requirements and consultation with stakeholders, staff will evaluate returning to
Council with a proposed ordinance codifying specific requirements and
enforcement measures.
Group 2: Gathering of Groundwater Information and Plans by Palo Alto and its
Partner Agencies
As discussed at the Policy and Services Committee, staff will continue working
with the Santa Clara Valley Water District (Water District) in an already ongoing
effort on developing a further understanding of the North County groundwater
systems, impacts of groundwater pumping, and opportunities for enhanced
groundwater recharge. A Water District key mission is to manage the County’s
groundwater; therefore, staff will collaborate closely with the Water District, and
the new Council-level Recycled Water Committee. This collaboration may also
include working with San Mateo County and its cities to ensure coordination with
their development of a groundwater strategic plan. Council may also wish to
refer review of this future work to the City’s Utilities Advisory Commission.
Staff will provide an update on the work plan for this effort to the Policy and
Services Committee in the first quarter of 2016.
Group 3: Further Ideas Brought Forward by Individual Policy & Services
Committee Members
Individual Policy and Services Committee members articulated additional ideas
and suggestions. Some of these ideas are multifaceted and complex, and will
require sustained effort from staff and assistance from consultants over multiple
City of Palo Alto Page 5
years. The Committee and City Council will need to evaluate priorities and
timelines, including the potential that significant new assignments may delay
other projects currently underway. Staff will prepare a report for the Policy and
Services Committee in the first half of 2016 to discuss these matters and the
development of a potential recommendation to Council to direct additional work
in one or more of these areas:
1. Charging for discharge of groundwater. The current fee for dewatering to
the storm drain system is $80 per month. This effort would consider
increased fees to charge for the use of the City’s storm drain system and staff
time to manage the dewatering requirements. Committee members
suggested exploring whether the fee that the Santa Clara Valley Water
District charges for groundwater pumping would be an appropriate baseline.
2. Developing dewatering requirements tailored to drought situation.
3. Developing approaches to ensure that multiple basement pumping is not
happening in close proximity (distance and time), and instead is spaced out,
essentially allowing only a limited number of basement construction
dewatering in one area.
4. Addressing potential damage from dewatering through bonds or insurance.
5. Further study of all pumping activities in the City, including private wells, City
Hall garage, Oregon Underpass and other underpasses.
6. Review of basement building and zoning code issues, including FAR
adjustments for basements and not allowing two-story basements, or any
basement, in areas with shallow groundwater. (Note: Staff’s initial reaction
is that utilizing zoning to implement these requirements may be quite
difficult because groundwater depth can vary significantly from block to
block)
7. Review of impacts of multiple basements on soil absorption and/or the
creation of barriers to groundwater flow.
8. Investigation of costs of other construction methods that do not require
City of Palo Alto Page 6
dewatering, or as much dewatering.
9. Investigate whether Palo Alto should assume a groundwater management
leadership role for the North County area. (Including consideration of staff
time and cost implications.)
10. In addition, Committee members were interested in how increased use of
permeable surfaces may assist with groundwater recharge. (Note: City staff
can provide an update on the new stormwater permit requirements for a
Green Infrastructure Plan which will require more infiltration of stormwater
into the ground rather than discharging it through storm drains via both
public and private projects.)
Group 2 is part of an ongoing effort and the Committee and City Council will be
updated periodically. Group 3 activities will be brought to the Committee
/Council for discussion and direction to study them; staff is making no estimate on
when they could be implemented.
Resource Impact
Testing and refining the suggested measures to improve the dewatering program
or any other measures suggested by the Committee will require significant staff
time that is currently allocated to other projects. For the homeowner, these
measures may increase basement construction project costs.
As mentioned in earlier parts of this report, Group 1 recommendations have sent
staff scurrying to develop final recommendations for action and are likely to
require additional ordinance language to be created and brought back to the City
Council for approval. Group 3 suggestions are varied and require thoughtful
review and potentially large costs. In every case, consideration of our ability to
fund and support or absorb the efforts will be required.
Environmental Review
The Group 1 suggested program enhancements are minor modifications to an
existing regulatory program designed to be protective of the environment. They
would be covered by the general rule that California Environmental Quality Act
(CEQA) does not apply where there is no possibility an action could have a
significant effect on the environment (State CEQA Guidelines Section
City of Palo Alto Page 7
15601(b)(3)). Group 3 requirements will be evaluated and appropriate
environmental review prepared as specific proposals are developed.
Attachments:
Attachment A - Policy and Services December Staff Reports (PDF)
Attachment B - Construction Dewatering Study Requirements (DOCX)
Attachment C - Correspondence (PDF)
City of Palo Alto (ID # 6268)
Policy and Services Committee Staff Report
Report Type: Agenda Items Meeting Date: 12/1/2015
City of Palo Alto Page 1
Summary Title: Basement Construction Dewatering
Title: Consider Tentative Staff Recommendations On Further Requirements
for Basement Construction Dewatering Program for 2016
From: City Manager
Lead Department: Public Works
Recommendation
Staff recommends that the Policy & Services Committee direct staff to continue
considering five program enhancements, presented in the “Discussion” section
below, on basement construction dewatering; and implement those found to be
feasible and practical by Spring 2016 to address public concerns raised during the
summer of 2015.
Executive Summary
Over the years, basement construction groundwater pumping has generated
public concern in Palo Alto; the ongoing drought and mandated water restrictions
this past summer escalating those concerns. Public concerns relate to the
apparent wasting of water by discharging to storm drains, potential impacts on
groundwater elevation and flow volume, as well as potential impacts on
neighboring properties, such as subsidence and cracks, and impacts on trees and
other landscaping.
In response to these concerns, staff has developed potential enhancements to the
City’s existing regulations regarding construction dewatering for review and
discussion.
Background
Basement construction is often required for non-residential, mixed use and
multifamily residential buildings, particularly if underground parking is included in
Attachment A: Policy and Services December Staff Reports
City of Palo Alto Page 2
the proposal.1 Additionally, the high value of land and housing in Palo Alto
translates into residential property owners seeking to increase their single family
homes by constructing basements. Basements constructed in R-1 districts do not
count towards allowable square footage (regulated by floor area ratio) and can be
quite large when located underneath the entire building footprint (PAMC Section
18.12.090). In 2015, 13 residential sites were conducting basement construction
groundwater pumping, with 12 of these sites constructing a basement as well as a
second story.
Basement construction groundwater pumping occurs when a basement is
constructed in areas of shallow groundwater, typically in the neighborhoods
closer to the bay or near former creek beds. Perimeter wells are established to
draw down the groundwater allowing for construction of the basement.
Dewatering continues until enough of the house has been constructed to keep
the basement in place. The groundwater being pumped is not potable (i.e.
drinkable). The Santa Clara Valley Water District regulates the groundwater basin
in Santa Clara County, but does not regulate incidental pumping associated with
basement dewatering.
Summary of Current Regulations
The City of Palo Alto has long regulated several aspects of basement groundwater
pumping for both residential and commercial sites. Geotechnical investigations
are required for basement construction and dewatering permits must be obtained
when groundwater is likely to be encountered and dewatering needed. The
permit is used, in part, to prevent pumping from October to April ensuring
adequate storm drain system capacity during winter months. City of Palo Alto
staff verifies that construction dewatering meets requirements for pH and
sediment prior to allowing discharge to the storm drain system, meeting State of
California stormwater regulations.
Unlike most Bay Area cities, Palo Alto does not allow drains around basement
foundations, collecting water and pumping to the storm drain continuously;
instead basements must be constructed to be waterproof.
1 In commercial and multi-family zones, basements used for parking are generally not counted towards allowable
floor area, but basement space containing usable space is. This report focuses on basements in R-1 neighborhoods
which have been the subject of most of the community concern.
City of Palo Alto Page 3
In 2008, the Planning and Transportation Commission held hearings on the
dewatering issue and a literature review prepared by EIP Associates was
presented (Attachment A).
In Summer 2014, the City’s Public Works Department (PWD) piloted a truck fill
station at a dewatering site to address public concern regarding the apparent
wasting of pumped water to storm drains during the drought. Following the
success of this first truck fill station, all basement groundwater pumping sites,
except those located in known groundwater contamination areas, were required
to install truck fill stations based on PWD specifications (Attachment B). The
stations accommodate large diameter and garden hoses as well as bucket filling.
Outreach includes dewatering sites published and mapped on the City website
(http://www.cityofpaloalto.org/gov/depts/pwd/pollution/recycled_n_other_non
_potable_water.asp), informational door hangers provided to contractors for
distribution to neighbors of the construction dewatering site (Attachment C), and
a Frequently Asked Questions document (Attachment D). Usage tracked with log
sheets showed some sites used extensively by neighboring properties, while
others saw little use. The City’s water truck utilized dewatering sites for tree and
median irrigation.
During the summer 2015 staff met with contractors to discuss additional ideas to
address public concerns. Contractors advised staff of the uniqueness of Palo Alto
in imposing standards on dewatering and requiring use of the pumped
groundwater, believing the requirements increase pumping duration and project
cost. One contractor stressed users could be injured at the fill stations, leading to
potential liability. Other than increasing public outreach, no new solutions to
decrease pumping or increase utilization of groundwater were identified.
Discussion
In Summer 2015, sites beginning the permit process were required to develop a
Use Plan to maximize the use of the pumped groundwater. Additional
requirements suggested by members of the public include a moratorium on
basements until further study is performed, more detailed review of basement
construction projects, minimizing pumping by using other methods for
dewatering or increasing weight on basement slab, requiring use of all the water
being pumped, payment for water pumped and directing water to the sanitary
City of Palo Alto Page 4
sewer. See Attachment E for correspondence from the public and Attachment F
for a petition submitted regarding the basement construction moratorium.
Using adaptive management based on learnings from this past summer, staff is
proposing to investigate the following program enhancements for basement
dewatering in 2016:
1. Encouraging greater fill station use by distributing more door-hangers and
enlisting other public outreach regarding dewatering, fill stations and trees.
This will be a contractor requirement and City activity.
2. Strengthening outreach on the water cycle and value of fresh water flows
to storm drains, creeks and bay.
3. Refining requirements for contractor Use Plans, including maximizing on-
site water use, one day per week water truck hauling service for neighbor
and City landscaping and piping to nearby parks or major users where
feasible. Contractors will be responsible for implementation of Use Plans.
4. Expanding fill station specifications to address water pressure issues
resulting from multiple concurrent users, including separate pumps for
neighbors where needed and sidewalk bridges for hoses to reduce tripping
hazards. Contractors will be responsible for implementation.
5. Broadening the City’s Basement Pumping Guidelines to specifically require
a determination of impacts of groundwater pumping on adjacent buildings,
infrastructure and trees or landscaping. Applicants would determine the
approximate location of the temporary groundwater cone of depression
caused by pumping. Avoidance measures would be required if impacts are
anticipated. Urban Forestry staff may develop guidelines for avoidance
measures such as soil enhancement and supplemental watering (by project
applicant) of neighboring landscaping. Additional measures could include
adjusting the location, depth or duration of pumping or altering
construction methods.
In addition, staff will request assistance from the Santa Clara Valley Water District
to continue to evaluate any potential effects of basement pumping on deep
City of Palo Alto Page 5
groundwater levels, particularly related to the City of Palo Alto emergency wells.
This issue is partially addressed in a previously provided 2003 report to the City by
Carollo Engineers (Attachment G). If additional actions by the City are needed,
they will be forwarded to the Policy and Services Committee prior to the 2016
construction season, along with the finalization of the above five
recommendations.
Resource Impact
Testing and refining the suggested measures to improve the dewatering program
or any other measures suggested by the Committee will require staff time that is
currently allocated elsewhere. These measures may increase basement
construction project costs.
Staff is seeking approval of Staff exploration of the named activities. One of the
elements to be explored is the amount of staff time needed for implementation,
and whether the additional time can be absorbed into existing staffing levels.
While Staff time is not expected to be large, Staff will be reporting back to the
Committee on this issue.
Environmental Review
The suggested program enhancements are minor modifications to an existing
regulatory program designed to be protective of the environment. They would be
covered by the general rule that California Environmental Quality Act (CEQA) does
not apply where there is no possibility an action could have a significant effect on
the environment (State CEQA Guidelines Section 15601(b)(3).
Attachments:
Attachment A: 2008 Planning and Transportation Division Study Session Regarding
Basement Construction Impacts (PDF)
Attachment B: New Aquifer Filling Station Specifications (PDF)
Attachment C: Doorhanger (PDF)
Attachment D: Groundwater Pumping from Building Sites FAQ (PDF)
Attachment E: Correspondence (PDF)
Attachment F: Basement Moratorium Petition (PDF)
Attachment G: Groundwater_Supply Report (PDF)
to address zoning criteria for light wells and below grade patios, but the pertinent code section is
provided and some of the issues may affect those provisions.
DISCUSSION
The discussion below summarizes recent basement construction statistics, the issues addressed in
the Public Works memo, the existing Public Works dewatering policy, potential impacts on
neighboring properties, and the use of concrete in basement construction and its implications for
the City's Green Building program. A few options for addressing public concerns are provided at
the end of the section.
Recent Basement Construction
The City's Building Division reports that there were permits for 65 new single family residential
basements issued over the past 2 years (through June 30, 2008). In that timeframe, there were a
total of 181 new single family home permits, excluding the detached condos for Sterling Park
(96 units). Ten (10) of the basements (of the total 65) were constructed for major
renovations/rebuilds. Basement construction has increased as compared to prior years, with an
average of about 22 bas.ement permits issued from 2001-2004.
The Public Works Department estimates that, of the total number of permits for basements in
recent years, approximately 5 per year require dewatering permits. In calendar year 2008 thus
far, the Department has issued 3 dewatering permits, and does not anticipate issuing any others,
given the proximity to the wet weather season. Attachment G provides a map of the depth of
groundwater in Palo Alto, as mapped by the Santa Clara Valley Water District.
June 9 Public Works Informational Memo
The June 9, 2008 Informational Memo from Public Works (Attachment A) addresses many
issues raised by the Council, Commission, and the public, including discharge volume of
dewatering, pump noise, water table impacts, subsidence, tree impacts, contaminated
groundwater migration, discharge of groundwater after basement construction, basement
excavation, and storm drain capacity. In some areas of technical impact, such as water table and
subsidence impacts, the memo refers to a study prepared by EIP Associates, Inc. in 2004
(Attachment D), which staff feels adequately addresses those specific concerns. Other concerns
regarding pump noise, contaminated groundwater contamination, and discharge of groundwater
after basement construction, are addressed in the Council memo but not discussed further here.
The discussions below focus on the key issues of discharge volumes and dewatering policy, the
impacts of basement excavation on neighboring sites, and the green building implications of
basement construction.
Discharge Volumes
The Public Works Department's "Basement Excavation Dewatering and Basement Drainage
Rules" (Attachment B) require a dewatering plan and permit for each site where dewatering
during basement construction is proposed. Groundwater levels must be identified in a
geotechnical report prior to permit review. Drawdown wells are typically installed around the
perimeter of the excavation and pump water out of the shallow aquifer to draw down the level of
the groundwater so the basement can be constructed without water filling the excavation. Public
Works estimates that draw down well systems for dewatering during basement construction can
pump approximately 30-50 gallons per minute of water non-stop for 3-6 months or more while
City of Palo Alto Page2
the basement is constructed. The rules now have been revised to limit dewatering to the months
of April through October. The total volume of water pumped into the storm drain system from a
dewatering operation is substantial, typically a few million gallons. However, the groundwater
level is re-established rapidly after dewatering ceases and the discharged water ultimately
remains within the water regime and may replenish aquifers downstream or may flow to a creek
or the Bay. Nevertheless, some water is surely lost in the process and the storm drain system is
burdened by the additional flow.
The Public Works Department's Basement Exterior Drainage Policy (Attachment C), last revised
October 1, 2006, prohibits the use of perforated pipe systems for basement drainage and requires
that all new basements be designed so that ongoing discharge after construction is not required
(with limited exceptions for basement-level exterior spaces).
The key issue for Commission discussion is whether it is appropriate to further limit or prohibit
basement construction where dewatering is required.
Impacts on Neighboring Properties
Another set of concerns about basement construction relates to potential impacts to neighboring
properties, including subsidence, effects on trees, and site stability.
• Site stability-Residents have reported concerns about the proximity ofbasement
excavation to their property line, which might result in erosion or undermining of the
property or nearby buildings. Various excavation shoring restrictions exist to protect
neighboring sites, and shoring plans are required by the Building Division. The Zoning
Code only allows basements below the main structure, so setbacks should be met, but
light wells are permitted to encroach up to 3 feet from a side property line (for a distance
of not more than 15 feet), and excavation for the basement wall may then extend to the
property line. Attachment F outlines the zoning code provisions for basements in the R-1
zone district.
• Trees -Tree impacts on the subject property or an adjacent site could occur from either
excavation damage to roots or from dewatering to a point where the roots dry out. The
Planning Arborist, however, reviews all projects to determine whether basements would
adversely impact an adjacent tree's root system, and plans would need to be revised if
impacts are identified. The Zoning Code requires that basement design would not
adversely impact any mature trees. The Planning Arborist has also noted that water
sources for most trees' roots are not as deep as the groundwater table.
• Subsidence -Staff believes that subsidence impacts, if any, are negligible from
dewatering, as the water table quickly returns to pre-dewatering levels and the duration of
dewatering is not long enough for soils to compress. Staff is aware of no demonstrated
subsidence impacts from basement construction dewatering, though some residents have
maintained that such an impact has occurred. The EIP study and contact with USGS have
also indicated negligible impact.
The key issue for Commission discussion is whether some change in policy or codes, such as a
minimum setback for excavation, would better protect neighboring properties without unduly
infringing on the potential for property owners to construct basements.
City of Palo Alto Page3
Green Building Regulations and Implications of Basement Construction
Basement construction has been identified as a "green building" issue due to the extensive
amount of energy required to produce the concrete used for basements. Concrete creates more
than 5 percent of the world's C02 emissions, at a rate of about 400 pounds of C02 for each cubic
yard of concrete (3 ,900 pounds). The cement component of concrete (7-15 % ) is the major source
of greenhouse gas emissions, and about 0.9 pound of C02 is created per pound of cement
produced, according to the Portland Cement Association. A second sustainability issue is the
amount of water discharged during dewatering during basement construction (discussed above).
The City's Green Building regulations (Attachment E) became effective on July 3, 2008. The
regulations include requirements to comply with green point rating systems for both
nonresidential (Table A) and residential (Table B) development. The definition of "square
footage" includes basement square footage, and the green points required for residential
development increase with each 70 additional square feet of house size. Thus, the ordinance does
not directly limit basement construction, but does require compensation in the form of increased
green point rating for a home with a basement. It should also be noted, however, that due to the
insulating qualities of the surrounding earth, basements are often more energy efficient than
above grade floor space.
For the Commission's information, Attachment K is an article that outlines work currently
underway by a Stanford professor to produce a "green" cement that would not only eliminate
C02 emissions from cement production, but could also use C02 emitted from other sources,
reducing those gases as well. A ways off, perhaps, but a potential solution to the adverse impacts
of concrete use in basements.
The key issue for the Commission is whether there is a basis for either limiting basement
construction or requiring further increases in green points criteria for basement construction to
minimize the carbon emissions impacts of basements.
POTENTIAL OPTIONS
Staff believes that the City's review policies generally protect neighboring properties from
deleterious effects of basement dewatering and that dewatering does not have substantial effects
on groundwater or result in the discharge of contaminated groundwater. However, water
discharge from dewatering can be substantial and there may be opportunities for the City to enact
policies or regulations to further minimize the loss of water from local sites as an enhanced
sustainability effort. Similarly, the City's Green Building regulations already require
compensation for basement construction in the form of additional green building measures to
achieve the stipulated point totals, but there may be revisions that would provide further green
building benefits where basements are constructed or to encourage retention of existing
basements in commercial areas. Some of the options available to the City may include, but are
not limited to:
1. Continuing to permit basements, with continued staff analysis of technical data and
impacts.
2. Prohibiting basement excavation within 3 feet of a low density residential property line.
City of Palo Alto Page4
3. Limiting basement construction based on the amount of water to be discharged or further
limit the timeframe for basement dewatering.
4. Modifying green building requirements to double basement square footage to determine
the number of GreenPoint Rated points required, and/ or allowing reductions for the use
of basement construction materials that reduce the embedded energy of concrete.
5. Allowing existing basements for nonresidential properties to be excluded from floor area
calculations if restricted to non-habitable uses, even ifthe basement meets Building Code
requirements for habitable space.
Subsequent to comments by the Commission, staff will return with specific recommendations for
policy or code changes to address basement issues. The Commission would then forward these
changes to Council for review and approval.
ENVIRONMENTAL REVIEW
No environmental review is required for a study session. The level of environmental review
required, if any, for potential code or policy actions will be determined once those actions are
identified.
ATTACHMENTS
A. June 9, 2008 "Basement Construction and Dewatering Impacts" Informational Memo to
City Council from Public Works Department
B. Public Works "Basement Excavation Dewatering and Basement Drainage Rules"
C. Public Works "Basement Exterior Drainage Policy," dated October 1, 2006
D. "New Basement Construction and the Groundwater Regime in Palo Alto," Technical
Memorandum prepared by EIP Associates, Inc., 2004
E. Green Building Tables for Residential and Nonresidential Development
F. Section 18.12.090 of the Zoning Ordinance re: Basements in R-1 District
G. Map of Depth to First Water, Santa Clara Valley Water District, October 15, 2003
H. May 8, 2008 E-mail from Steve Broadbent
I. July 19, 2008 E-mail from David Stonestrom
J. April 22, 2008 E-mail from Jody Davidson
K. "Green Cement May Set C02 Fate in Concrete." San Francisco Chronicle. September 2,
2008.
COURTESY COPIES
Architectural Review Board
Jody Davidson
Steve Broadbent
David Stonestrom
John Northway
Bob Morris, Public Works
REVIEWED BY: Julie Caporgno, Chief Planning and Transportation Official
DEPARTMENT/DIVISION HEAD APPROVAL: __ ~----·-~--~---· ___ _
City of Palo Alto
Curtis Williams
Interim Director
Page5
To assist Council in understanding the differences between shallow and deep aquifers _(described
·more completely in EIP's·attached report), staff provides the following descriptions.
Shallow aquifers are formed by rain seeping through the ground and pooling close to the ground
surface. The top surface of the shallow aquifer is called the water table and is typically 10-30
feet below the ground surface in most areas of Palo Alto other than the hills. This is the aquifer
that basement excavations may extend into, necessitating dewatering. Shallow aquifer water is
nonpotable. as it does not meet drinking water standards. ·
Deep aquifers are separated from the shallow aquifers by impermeable sediment layers, like rock
or clay, called aquicludes that prevent shallow aquifer water from reaching the deep aquifers. In
Palo Alto, the deep aquifers are approximately 200 feet below the ground surface. Dewatering
basement excavations has virtually no effect on the deep aquifers .
. Certain layers of permeable sediment, like sand or gravel, may trap and hold pockets of
groundwater temporarily between shallow and deep aquifers, but these are typically not affected
by basement dewatering operations. . .
Below is a brief summary of the above research organized by community key concerns.
Discharge Volume .
A soils report is required for all projects with basements or underground garages. This report
determines the depth to the shallow aquifer below the ground surface. If a contractor believes
the excavation will go into the groundwater, they will typically submit a drawdown well
dewatering plan to Public Works. Drawdown wells are· typically installed around the perimeter
of the excavation and pump water out of the shallow aquifer to draw down the level of the
groundwater so the basement can be constructed without groundwater filling the excavation.
These drawdown well systems pump approximately 30-50 gallons per minute into the storm
drain system non~stop for 3-6 months while the contractor constructs the basement.
The volume of water pumped into the storm ·drain system from a drawdown well dewatering
operation is substantial, typically a few million gallons. It could be used as landscaping water,
but it is too large a volume for individual use and too impractical to capture and reuse for other
use.
The water pumped out of the ground is discharged into the storm drains, which typically
discharge into the creeks. San Francisquito Creek is a losing creek, meaning that water is lost by
seeping through the creek bed and into the shallow aquifers. So, in this case, water pumped out
of the shallow aquifers is added back to it. For water pumped into lined creeks, the water flows
to the bay and is lost to the aquifer.
The volume of groundwater pumped out of an excavation site is a small fraction of the . total
volume of the aquifer and does not deplete or lower the aquifer, except, of. course, in the
immediate vicinity of the excavation. The USGS reports that due to natural (rain) and manmade
(irrigation, leaking sewer pipes, and the SCVWD's groundwater recharge program) methods,
more water is recharged into the shallow aquifers than is pumped out of it by all pumping in the
Santa Clara Valley. The EIP report also confirmed that the water table is only drawn down
CMR:266:08 Page 2of5
locally (within tens of feet of the excavation) and· reestablishes itself quickly after dewatering
ceases. Therefore,the cumulative effect ofdewatering on the shallow aquifers is negligible.
Pump Noise
Dewatering pumps can make excessive noise if installed improperly, and this is a concern for
neighboring residents since the pumps run 24 hours a day. Public Works is tightening the
requirements for pump operation to eliminate this problem.
Water Table Impacts
While the City currently prohibits basements in flood zones, there is no blanket prohibition
against construction in areas with shallow aquifers. Basements are not typically constructed so
deep that they actually go into the water table, but they do ·in some cases. In other cases, the
water table might rise up, as at the end of a particularly wet winter, and surround a basement.
However, in these cases, the water table level and the flow of the groundwater are not changed
due to the presence of basements, as reported by EIP.
Subsidence
Land settlement, or·subsidence, caused by temporary (such as 6 months) construction dewatering
is negligible, as reported by EIP and USGS. For subsidence to occur, dewatering needs to occur
over a number of years.
Tree Impacts Relative to Water Table Changes
The Planning ·Division arborist reports that in most of the developed areas · of Palo Alto the
preponderance of absorbing tree roots are not . found in lower soil horizon levels below seven
feet Therefore, the majority of temporary dewatering projects are not expected to impact trees.
If a tree's roots are however deep enough and have been determined, on the basis of a certified
arborist report or other ·qualified assessment, to be dependent· on the water table, theri the
mitigation would be for the , contractor to provide separate irrigation for the tree( s) during the
dewatering period.
Contaminated Groundwater Migration
Citizens have expressed a concern that large volumes of groundwater being pumped out of the
aquifers might cause nearby contaminated groundwater plumes to migrate towards the pumping
site. When an application is submitted, staff checks dewatering sites against known
contaminated groundwater plume maps. If a site is within a certain proximity to a known plume,
staff requires the water to . be tested for contaminants prior to and during discharge. The
contractor must retain an independent testing service, test for the contaminants Public Works
specifies, and submit those results to Public Works. If the water is contaminated, as it was in one
case near the Stanford Research Park superfund site, it must be treated before it can be released
or discharged to the sanitary sewer under permit from Public Works. The CRWQCB is drafting
requirements for contractors to test groundwater discharged to the storm drain system. Staff
awaits the adopted version of these requirements, scheduled for this summer, and will implement
them at that time. To date, there has been no evidence that contaminated groundwater has been
discharged into the storm drain system or that contaminated groundwater plumes have migrated.
CMR:266:08 Page 3of5
Discharge of Groundwater after Basement Construction
A few years ago, Public Works allowed the use of perforated drain pipes to be installed behind
basement walls and under basement slabs when the geotechnical engineer reported that
groundwater would not ri.se to the level of. these pipes. The pipes are installed . to .capture
rainwater that filters through the ground and collects behind basement walls in order to minimize
the chance of the water leaking through the walls. The pipes drain, to a sump where a pump then
.. pumps the water to the street gutter.· Unfortunately, after some wet. winters, groundwater did rise
up to these pipes and was then pumped c~mtinuously into the street gutter for long periods of
time, creating a number of public nuisance and safety concerns. Accordingly, Public Works
adopted a policy two years ago that prohibits the use of perforated drain pipes· for basements in
areas of the City with relatively high groundwater (east of Foothill Expressway) to eliminate
•these potential nuisances. Public Works also re.commends that applicants for. new basement
projects retain a waterproofing consultant to ensure tile basement does riot leak. .
Older basements that were permitted with perforated drain pipes still may occasionally discharge
groundwater into the street gutter. Public Works addresses these cases by working with the
homeowners to eliminate the discharge, typically accomplished by having the homeowner raise
the pump in the sump above the level of the groundwater.
Basement Excavation
Some residents have expressed a concern that the excavation pit for a basement comes too close
to adjacent properties, potentially jeopardizing the stability of these properties. Although this
strictly does not relate to dewatering, staff recognizes it as a legitimate concern. As previously
mentioned, the Building Division requires geotechnical reports for all projects that involve
basements or underground structures. · A standard feature of these ·reports is recommendations
. artd requirements from the geotechnical engineer that specify measures . to stabilize ·the
excavation during construction. The Building Division inspects all basement construction to
ensure conformance with the geotechnical report and to .verify all recommended stabilization
measures are implemented. In addition, Building Inspectors will require the contractor to install
extra precautionary measures before work can continue.
Storm Drain Capacity
Staff is concerned that dewatering basement excavations. may take. up too much capacity in the
City's storm drain pipes, minimizing the system's ability to accommodate storm water and
potentially causing or exacerbating flooding. This is not a concern raised by citizens, nor has
there been any incidents where dewatering has caused flooding, but staff is developing some
guidelines for wintertime dewatering in an effort to avoid a problem. The draft guidelines
currently disallow dewatering during the winter unless an exemption is granted by the Director
of Public Works.
CONCLUSION
Staff has researched and analyzed each of the concerns about dewatering raised by citizens.
Based on that research, staff believes that the cumulative effects of dewatering · basement
excavations has minimal impacts on the City and that the practice should be allowed to continue.
The attached EIP report essentially comes to the same conclusion. The number of residential
basements permitted in the City has increased from approximately 20 a year at the start of the
decade to approximately 30 a year currently. However, Public Works only issues about 5-10
CMR:266:08 Page 4 of 5
. E. JJl ..
~"fJ: !2~·· ••• ••.
. ~ . . .· . . .· .,.....__
ATTACHMENT A
A S S 0 .C l A T t:: S
Draft Technical Memorandum: Correlation between New Basement
Construction and the Groundwater Regime in Palo Alto, California
lo ·Statement of the Plannjng and Transportation Commission's
concerns.·
At the 14 J anua1y 2004 Commission meeting, the planning staff presented a number of
. .
proposed changes to the existing regulation of basements in the R-1 zones. During the
ensuing discussion, several Commission members expressed conc~rns about the impact of
basement construction on groundwater levels and flow directions. Eight specific,
interrelated issues were identified.
II
· 111
II
II
Is groundwater pumping causing or contributing to land subsidence?
What are the effects of pumping for months to dewater a basement constmction
site?
Are basements bemg permitted in some inappropriate areas [where the water
table is only a few feet below the ground surface], creating the need for
continuous pumping?
What groundwater effects occur if water is withdrawn from the water table and
pumped into the sewers or creeks? ·
• . What groundwater diversion effects occur if basement walls are built along
•
•
•
creeks and/or perforate aquifers? ·
What are the effects on landowners adjacent to, and down gradient from,
pumping sties? ·
What are the cumulative effects of basements on the groundwater regime?
Can basement regulations be crafted to address the hydro-geology of specific
building sites? · .
The general concern underly.iiig these issues was expressed by Commissioner
Annette Bailson: the Commission does not have the information needed to identify whether
these are issues of concern, or to make informed decisions on the issues. The remainder of
this technical memorandum seeks to respond to that underlying concern by provide some
background information about the listed issues and about groundwater hydrology of the City
relative to the constmction of basements.
Page 1of7
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2. Differences. between shallow (surface) and deep (confined) .
groundwater aquifers.
· Defining the Aquifers
An aquiferis a body of geologic material, usually rock or some mixture of gravel, sand, silt
and clay, that is sufficiently permeable to conduct groundwater. Some definitions include
the stipulation that the body produce an economically significant flow of water before it may
be considered an aquifer. For the purposes of this technical memorandum, the broader
. .
definition is applied to allow for easier discussion ofthe water-bearing formations underlying
the City.
Of the various types of aquifers, two are of particular interest in this discussion: the shallow
or surface aquifer, and the deep or confined aquifer. The relative terms 'shallow' and 'deep'
refer to the depth of the aquifer below the surface of the ground (usually expressed as
'number of feet bgs' in hydrology studies).
A surface aquifer is so named because it is open to the surface of the ground. Rain falling
on the ground surface seeps through the soil (infiltration) to some depth where it pools to
form a more or less continuous body of water occupying the spaces between sediment
particles or rock fragments (groundwater). The top of this body of groundwater is the water
table. In the Santa Clara Plain, which forms the lowlands of Palo Alto, the water table
occurs at depths of as little as ten feet below the ground surface.
Being open to the surface of the ground, the surface aquifer is subject to the influertces of
overlying land cover and land uses. Modern stream channels, such as the numerous reaches
of San Francisquito Creek, intersect or overlie the surface aquifer, extracting water from it or
adding water to it. Paving and construction create artificially impermeable surfaces that
prevent local direct infiltration to the surface aquifer. Cherriical constituents in urban and
agricultural runoff enter the surface aquifer through infiltration from channels or detention
basins, lowering the quality of the groundwater. Leaking landfill cells, leaking underground
stornge tanks, and liquid spills also contribute to the reduction of water quality in the surface
aquifer. Although current stewardship has slowed water quality deterioration, the surface
aquifer still cannot be used as a source of potable water.
A confined aquifer is one tha.t is separated hydrologically from the overlying and underlying
sediments and rock and from other aquifers. Usually the separating agent (called an
aquiclude) is formed by a layer of impermeable sediment, such as clay, or by iffipermeable
. rock, such as unfractured granite. The confined aquifer is not connected directly to the
overlying ground surface and is separated from the surface aquifer by an aquiclude. It is, in
effect, a separate hydrologic system, gaining water from_ some distant source (i.e., not local
Page 2of7
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/\SSOC!AlES
rainfall). and transmitting it to some other relatively distant discharge area. Bec.:ause the
.. confined aquifer is below, and hydrologically separated from; the surface aquifer, it is, by
definition, a deep aquifer, irrespective of the number of feet it is below the ground surface.
Several aquifers tnay underlie each other. This is the case beneath the Santa Clara Plain
where geologically recent stream-hid (alluvial) gravel, sand, silt, and clay form a sequence of
· deposits nearly 1500 feet thick between the foothills of the Coast Ranges and San Francisco
. .
Bay. Channels of ancient rivers depositing this material have been cut off and filled by
succeeding intersecting channels, which, in turn, have been buried by the deposits of more
modern channels. In this way a complex series of sediment layers of unconsolidated
(loose), partially consolidated (dense), and consolidated (very dense) material has been built
up as the Santa Clara Plain~ The layers are discontinuous and of greater or lesser
permeability, depending on their density and clay of silt content.
A complicating factor in examining such a series of aquifers is that often they are not
completely confined. The aquicludes separating the aquifers may not be totally impermeable
(in which case· they are called aquitards). allowing water to seep from one aquifer to another.
The aquifers may be connected within or outside the local area, arising from a common
source or flowing to a common discharge area. The aquifers may be connected artificially
through leaks in wells or along pilings passing through the aquifers. Beneath the portion of
the Santa Clara Plain in Palo Alto, there is a confining clay layer that separates the surface
aquifer from the deeper aquifers, but, on a regional level, this separation attenuates and,
eventually, disappears farther south in San Jose ..
Being separated from the surface aquifer in this part of the Santa Clara Plain, the confined
aquifers beneath the City are not subject to the. direct influences previously described for
land cover and land uses above the surface aquifer. To the extent that groundwater migrates
from the southern part of the Santa Clara Plain groundwater basin to the northern part, the
effects of similar land cover and land uses in areas toward San Jose may affect water quality
in the deep aquifers beneath Palo Alto.
Construction-period Dewatering Effects
. In general, cons~ction-period dewatering effects are limited to the surface aquifer. This
would not necessarily be the case for major high-rise construction where foundations and
below-grade levels may extend 100 or more feet beneath the ground surface, increasing the
. chances of encountering confined aquifers. It is, however, the case for the type of
relatively shallow basement construction being considered in the Zoning Ordinance Update.
. In the Santa Clara Plain portion of Palo Alto, the uppermost sequence of unconsolidated
and partially consolidated alluvium is about 200 feet thick. This sequence contains the
Page 3of7
ASSOCJJ,TES
surface aquifer~ the base of which is the previously mentioned clay aquiclude identified by
the Santa Clara Valley Water District (SCVWD) in its 2001 Groundwater Management Plan.
The general direction of groundwater flow in this area is northeast toward the Bay, so the
surface aquifer and_ the _deeper, confined aquifers tend to remain separated in Palo Alto until
they reach the vicinity of the Bay margin.
The removal of groundwater from an excavation during below-ground-level construction is
necessary to provide safety for the construction workers, and .is a prerequisite for
wate1proofing the building's foundation and subsurface floors. One method for
accomplishing this is to dig a small pit below the base of the foundation excavation, slope
the excavation so groundwater drains to the pit, and then pump the water out of the pit and
into the storm drainage system .. Another method is to drill temporary wells around the
building footprint and pump directly from the groundwater body to the storm drainage
system until the local water table drops below the base of the excavation. In either case,
groundwater flowing into the area of drawdowrt created by the dewatering process is
deflected toward the base of the excavation, whence it is pumped to the storm drainage
system. Groundwater beyond the influence of the dewatering process continues to flow
normally.
Dewatering pumping continues until the foundation and subsmface floors are completed
and the excavation is filled. The amount of water deflected depends on the level of the
water table, the permeability of the material adjacent to the excavation, and the length of
time th~ excavation needs to be kept open and dry. An increase in any of these factors ·
increases the amount of water deflected. This amount is small when compared to the total
volume of available groundwater directly beneath the Santa Clara Plain (see below). Because
the deflection is temporary and very localized, and because groundwater levels at the sites
recover rapidly once pumping has ceased, there appears to be no discernable long-tetm
effect on the surface aquifer.
In the areas adjacent to the site being dewatered, the water table would be lowered
temporarily by the dewatering process. This effect could extend from several feet to several
tens of feet beyond the excavation depending on ·the method used, the level of the water
table at the time dewatering began, the permeability of the material adjacent to the
excavation, and the length of time the excavation needed to be kept open and dry. The
possibility exists that adjacent landscaping could be experience deterioration from reduced
·groundwater availability.
Defleetion or Reduction of the rate of Groundwater Flow
Although the amount of water pumped from an excavation may appear substantial as it
Page 4of7
A ·s S () C l A l · E S.
flows along a street to a storm drain inlet, it is small compared to the amount of
groundwater directly beneath the Santa Clara Plain. The _SCVWD's current estimate is that
there is more than 350,000 acre-feet of groundwater available in the Santa Clara Sub basin .
. An excavation dewatering flow of 1 cubic foot per second would deflect 1.98 acre-feet of
· water per day. Because groundwaterwoUld be pumped out of the excavation faster than ·
could flow in, the ~~teration in groundwater flow rate would be less than the rate of
de\Vatering. Because t.he resultant groundwater flow ~eflectionis temporary; small, and very
localized, there appears to be no discernable long.oterm effect on the ·surface aquifer.
. .
Because dewatering for basement construction occurs only in the uppermost portion of the
surface aquifer, there would be no effect on the deep aquifer.
. . ..
In a typical 3-month excavation period tlie 1.98 acre:. . .feet per day dewatering flow would
amount to 0.05% (one-twentieth of one percent) of the minimum known groundwater
resource in the subbasin. No published information about the subbasin's water budget has
been found; so any to attempt to predict how quickly the watet would be replaced through
recharge would be speculative. It is known, however, that the importation of potable water
and the SCVWD controlled recharge program have assisted groundwater levels in the
sub basin to rise 200 feet during the last 40 years. Most of that rise has been in the surface
aquifer. The implication is that the subbasin is being recharged at a rate substantially higher
than the rate of withdrawal from all pumping, including dewatering for basement
construction. Consequently,it appears that the amount of flow from one, or even several,
dewatering operations would not have long-term effects on the surface aquifer.
In the.areas adjacent to the site beingdewatered, the rate and flow directions of the
groundwater would be altered temporarily by the dewatering process. Groundwater in the
influenced area would move toward the base of the excavation at a rate lower than the rate
.·of dewatering discharge. This effect could extend from several feet to several tens of feet
. beyond the excavation depending on the method used, the level of the water table at the
time dewatering began·,· the permeability of the material adjacent to· the excavation, and the
length of time the excavation needed to be kept open and dry. Flow directions and rates
would revert to near normal when dewatering ceased.
There would be some displacement of groundwater flow around the newly constructed
. basement, depending on the permeability of the surrounding soil materials. The volume of
space displaced by the basement could be several thousand to severai tens of thousands of
cubic feet, which, although small-compared to the volume of the surface ~quifer, could be
significant locally, especially if there were other similarly sized basements in the immediate
vicinio/. The flow of groundwater would readjust to this condition, possibly altering the
level of the water table in the vicinity of the site for· several weeks or months, but is unlikely
to experience any major permanent change. The groundwater level in the surface aquifer
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ASSOCJATES
undergoes more significant changes during the rainy season than would be expected from
long-term flow deflection caused by basements.
Saltwater Intrusion and Subsidence
Saltwater intrusion and subsidence in the Santa Clara Subbasin are documented regional
effects of the excessive removal of groundwater from the deep aquifer (overdrafting) o~er
. many years. This practice was curtailed in the mid-1960s when the importation of potable
·water increased substantially. Smee then, the SCVWD has been recharging the subbasin
thereby raising groundwater levels, impeding saltWater infiltration of the sutface aquifer,
and virtually eliminating further overdraft-related subsidence (the effects of previops ·
subsidence cannot be reversed because portions of the deep aquifer have been compressed
permartently). Such basin-wide effects could recur only if the deep aquifer became
overdrafted again. Because dewatering for basement construction occurs only in the.
uppermost portion of the surface aquifer and involves only a small amount of groundwater
withdrawal, no effects would occur in the deep aquifer.
3. Palo Alto Public Works Department existing regulatory structure.
There are a number of policies in place that provide protection for the City's groundwater
resource and for property owners in the vicinity of new basement construction.
•
•
•
•
•
The PublicWorks Department prohibits the long-term pumping ofgroundwater
after a basement has been constructed. This eliminates the possibility that the
w~ter ·table in the vicinity of the project would be lowered permanently.
The Public W or.ks Department requires basements to be waterproofed and
strengthened structurally below the expected groundwater level. This eliminates
the need for groundwater pumping.
The Public Works Department requires permit applicants whose projects would
have basements to prepare a geotechnical investigation and report that would
determine, among other information, the expected highest groundwater level in
the local shallow aquifer. This allows the department to make informed
decisions about the advisability of basement construct:lon at a particular site
and/ or to _set the conditions under which basement construction may proceed.
If dewatering is necessary for basement construction, the Public Works
Department sets the dewaterillg permit conditions based on the hydrology of the
specific site under consideration. This ensures resource and property protection
where it is needed.
The Public Works Department allows the removal of seepage water that collects
along basement walls above the water table. Normally this removal would need
only a minimal amount of pumping, but may need-to be monitored.
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4. Recommendation regarding the advisability of codifying groundwater
effects in the Zoning O_rdinance Update ·
The above-listed Public Works Department policies dealing with basement construction and
dewate:ring for such·constiuction are intended to prevent.substantial impacts to
groundwater, either on an area-wide basis or in the vicinity of the construction site.
Although the policies and their associated construction standards appear to address the . . . .
issues adequately, it may be advisable for the Public Works Pepartmerit to increase the
community's awareness of these issues through an out-reach program .. Because these issues
are, essentially, engineering concerns that are site-specific and already covered by existing
regulations, there is no need to modify the zoning ordinance with respect to them.
Sincerely,
George J. Burwasser,
EIP Associates
EIP ASSOCIATES 353 SACRAMENTO STREET SUITE 1000 SAN FRANCISCO, CALIFORNIA 94111
Telephone 415-362~ 1500 Facsimile 415-362-1954 E-mail .rf@eipas.wdaies.com
JJJ/ll/V.eipassodales.com
ATTACHMENT B
BASEMENT EXCAVATION DEWATERING
AND BASEMENT DRAINAGE RULES
BASEMENT DRAINAGE: Due to high groundwater throughout much of the City and
Public Works prohibiting the pumping and discharging of groundwater, perforated
pipe drainage systems at the exterior of the basement walls or under the slab are
not allowed for this site. A drainage system is, however, required for all exterior
basement-level spaces, such as lightwells, patios or stairwells. This system consists
of a sump, a sump pump, a backflow preventer, and a closed pipe from the pump to
a dissipation device onsite at least 10 feet from the property line, such as a bubbler
box in a landscaped area, so that water can percolate into the soil and/or sheet flow
across the site. The device must not allow stagnant water that could become
mosquito habitat. Additionally, the plans must show that exterior basement-level
spaces are at least 7" below any adjacent windowsills or doorsills to minimize the
potential for flooding the basement. Public Works recommends a waterproofing
consultant be retained to design and inspect the vapor barrier and waterproofing
systems for the basement.
BASEMENT SHORING: Shoring for the basement excavation, including tiebacks,
must not extend onto adjacent private property or into the City right-of-way without
having first obtained written permission from the private property owners and/or an
encroachment permit from Public Works.
DEWATERING: Basement excavations may require dewatering during construction.
Public Works only allows groundwater drawdown well dewatering. Open pit
groundwater dewatering is disallowed. Dewatering is only allowed from April
through October due to inadequate capacity in our storm drain system. The
geotechnical report for this site must list the highest anticipated groundwater level.
We recommend a piezometer to be installed in the soil boring. The contractor must
determine the depth to groundwater immediately prior to excavation by using the
piezometer or by drilling an exploratory hole if the deepest excavation Will be within
3 feet of the highest anticipated groundwater level. If groundwater is within 3 feet
of the deepest excavation, a drawdown well dewatering system must be used, or
alternatively, the contractor can excavate for the basement and hope not to hit
groundwater, but if he does, he must immediately stop all work and install a
drawdown well system before he continues to excavate. Public Works may require
the water to be tested for contaminants prior to initial discharge and at intervals
during dewatering. If testing is required, the contractor must retain an independent
testing firm to test the discharge water for the contaminants Public Works specifies
and submit the results to Public Works.
Public Works reviews and approves dewatering plans as part of a Permit for
Construction in the Public Street ("street work permit"). The applicant can include a
dewatering plan in the building permit plan set in order to obtain approval of the plan
during the building permit review, but the contractor will still be required to obtain a
street work permit prior to dewatering. Public Works has a standard dewatering plan
sheet that can be used for this purpose and dewatering guidelines are available on
Public Works' website. Alternatively, the applicant must include the above
dewatering requirements in a note on the site plan.
Attachment C
PUBLIC WORKS ENGINEERING
BASEMENT EXTERIOR DRAINAGE POLICY
EFFECTIVE OCTOBER 1, 2006
The Department of Public Works (Public Works) will not permit the use of basement exterior
drainage systems consisting of perforated pipes located on the exterior of the basement walls or
underneath the slab that collect water which is then pumped to the surface of the ground for
discharge, either on-site or off-site, for all City of Palo Alto parcels northeast (the bay side) of
Foothill Expressway.
Purpose
To ensure the public safety and health by preventing the discharge of groundwater into the City
gutter system. The discharge of groundwater into the gutter system causes the following public
safety, health and nuisance concerns:
• gutters are constantly wet and may enhance the growth of algae, thereby creating a
slippery condition for pedestrians, bicyclists and motorists
• ponded water at the low spots of the gutter may be slippery to cross for pedestrians,
bicyclists and motorists
• ponded water in the gutter may become mosquito habitat
• ponded water in the gutter may seep through cracks, undermining the subgrade and
degrading the gutter and adjacent pavement
• groundwater discharge into the City's storm drain system adversely affects others
who need to discharge storm water run-off for which the system was designed
Background
In the past, Public Works allowed perforated pipe basement drainage systems to collect water
behind basement walls and under basement slabs and discharge it at the ground. Architects
proposed these systems in order to minimize the chances of water leakage through the basement
walls and slabs. These systems were permitted with the intention of only collecting and
discharging small amounts of rainwater that had seeped down through the soil. For proposed
basement drainage systems, Public Works required geotechnical reports that estimated the
highest expected groundwater level at the site and Public Works required that the perforated
pipes be placed above this level. Recent experience indicates that oftentimes the groundwater
level rose above the estimated level and entered the perforated pipes, resulting in the constant
pumping of groundwater into the street gutter.
Analysis
Public Works has obtained a groundwater elevation contour map from the Santa Clara Valley
Water District. These maps were established using data from numerous water monitoring wells
the SCVWD maintains throughout the City. The contours are the depth below ground to the
highest level the main groundwater aquifer has risen to since the monitoring wells were installed.
The area of town where there is relatively high groundwater (above 20 feet below-grade) is
roughly northeast of Foothill Expressway.
The main aquifer depicted in the contour map is not the only source of groundwater. Due to soil
properties, groundwater can get trapped between two relatively impermeable layers of soil.
These lenses of perched groundwater can occur essentially anywhere and be of any size.
Consequently, even though the SCVWD map may indicate a certain area of town has
groundwater at 20 feet below-grade, for instance, there may currently be perched water closer to
the surface or perched water may occur in the future closer to the surface.
Summary
Public Works feels that the public safety and health, potential nuisance, and maintenance
concerns caused by the discharge of groundwater into street gutters outweigh the developers'
desire for perforated pipe drainage systems. Although certain sites may seem appropriate for
perforated pipe drainage systems because of current low groundwater levels, higher groundwater
levels may occur in the future. Accordingly, Public Works will no longer permit perforated pipe
basement drainage systems installed in order to discharge water at the ground surface northeast
of Foothill Expressway.
Drainage systems are required and will be permitted for basement-level exterior spaces, such as
stairwells, lightwells and patios. These drainage systems consist of a sump, a sump pump, and a
closed pipe from the pump to a dissipation device onsite, such as a bubbler box in a landscaped
area, so that water can percolate into the soil and/or sheet flow across the site. The device must
not allow stagnant water to occur that could become mosquito habitat. Additionally, the plans
must show 8" of freeboard between the floor of any exterior basement-level space and any
adjacent windowsills or doorsills.
Glenn Roberts, Director of Public Works
S:PWD/ENG/TYPING/Morris/Development/Basement Drainage/Basement Drainage Policy
ASSOCIATES
2. Differences between shallow (surface) and deep (confined)
groundwater aquifers.
Defining the Aquifers
An aquifer is a body of geologic material, usually rock or some mixture of gravel, sand, silt
and clay, that is sufficiently permeable to conduct groundwater. Some definitions include
the stipulation that the body produce an economically significant flow of water before it may
be considered an aquifer. For the purposes of this technical memorandum, the broader
definition is applied to allow for easier discussion of the water-bearing formations underlying
the City.
Of the various types of aquifers, two are of particular interest in this discussion: the shallow
or surface aquifer, and the deep or confined aquifer. The relative terms 'shallow' and 'deep'
refer to the depth of the aquifer below the surface of the ground (usually expressed as
'number of feet bgs' in hydrology studies).
A surface aquifer is so named because it is open to the surface of the ground. Rain falling
on the ground surface seeps through the soil (infiltration) to some depth where it pools to
form a more or less continuous body of water occupying the spaces between sediment
particles or rock fragments (groundwater). The top of this body of groundwater is the water
table. In the Santa Clara Plain, which forms the lowlands of Palo Alto, the water table
occurs at depths of as little as ten feet below the ground surface.
Being open to the surface of the ground, the surface aquifer is subject to the influences of
overlying land cover and land uses. Modern stream channels, such as the numerous reaches
of San Francisquito Creek, intersect or overlie the surface aquifer, extracting water from it or
adding water to it. Paving and construction create artificially impermeable surfaces that
prevent local direct infiltration to the surface aquifer. Chemical constituents in urban and
agricultural runoff enter the surface aquifer through infiltration from channels or detention
basins, lowering the quality of the groundwater. Leaking landfill cells, leaking underground
storage tanks, and liquid spills also contribute to the reduction of water quality in the surface
aquifer. Although current stewardship has slowed water quality deterioration, the surface
aquifer still cannot be used as a source of potable water.
A confined aquifer is one that is separated hydrologically from the overlying and underlying
sediments and rock and from other aquifers. Usually the separating agent (called an
aquiclude) is formed by a layer of impermeable sediment, such as clay, or by impermeable
rock, such as unfractured granite. The confined aquifer is not connected directly to the
overlying ground surface and is separated from the surface aquifer by an aquiclude. It is, in
effect, a separate hydrologic system, gaining water from some distant source (i.e., not local
Page 2of7
ASSOClATlr:S
surface aquifer, the base of which is the previously mentioned clay aquiclude identified by
the Santa Clara Valley Water District (SCVWD) in its 2001 Groundwater Management Plan.
The general direction of groundwater flow in this area is northeast toward the Bay, so the
surface aquifer and the deeper, confined aquifers tend to remain separated in Palo Alto until
they reach the vicinity of the Bay margin.
The removal of groundwater from an excavation during below-ground-level construction is
necessary to provide safety for the construction workers, and is a prerequisite for
waterproofing the building's foundation and subsurface floors. One method for
accomplishing this is to dig a small pit below the base of the foundation excavation, slope
the excavation so groundwater drains to the pit, and then pump the water out of the pit and
into the storm drainage system. Another method is to drill temporary wells around the
building footprint and pump directly from the groundwater body to the storm drainage
system until the local water table drops below the base of the excavation. In either case,
groundwater flowing into the area of drawdown created by the dewatering process is
deflected toward the base of the excavation, whence it is pumped to the storm drainage
system. Groundwater beyond the influence of the dewatering process continues to flow
normally.
Dewatering pumping continues until the foundation and subsurface floors are completed
and the excavation is filled. The amount of water deflected depends on the level of the
water table, the permeability of the material adjacent to the excavation, and the length of
time the excavation needs to be kept open and dry. An increase in any of these factors
increases the amount of water deflected. This amount is small when compared to the total
volume of available groundwater directly beneath the Santa Clara Plain (see below). Because
the deflection is temporary and very localized, and because groundwater levels at the sites
recover rapidly once pumping has ceased, there appears to be no discernable long-term
effect on the surface aquifer.
In the areas adjacent to the site being dewatered, the water table would be lowered
temporarily by the dewatering process. This effect could extend from several feet to several
tens of feet beyond the excavation depending on the method used, the level of the water
table at the time dewatering began, the permeability of the material adjacent to the
excavation, and the length of time the excavation needed to be kept open and dry. The
possibility exists that adjacent landscaping could be experience deterioration from reduced
groundwater availability.
Deflection or Reduction of the rate of Groundwater Flow
Although the amount of water pumped from an excavation may appear substantial as it
Page 4of7
ASSOCIATES
flows along a street to a storm drain inlet, it is small compared to the amount of
groundwater directly beneath the Santa Clara Plain. The SCVWD's current estimate is that
there is more than 350,000 acre-feet of groundwater available in the Santa Clara Subbasin.
An excavation dewatering flow of 1 cubic foot per second would deflect 1.98 acre-feet of
water per day. Because groundwater would be pumped out of the excavation faster than
could flow in, the alteration in groundwater flow rate would be less than the rate of
dewatering. Because the resultant groundwater flow deflection is temporary, small, and very
localized, there appears to be no discernable long-term effect on the surface aquifer.
Because dewatering for basement construction occurs only in the uppermost portion of the
surface aquifer, there would be no effect on the deep aquifer.
In a typical 3-month excavation period the 1.98 acre-feet per day dewatering flow would
amount to 0.05% (one-twentieth of one percent) of the minimum known groundwater
resource in the subbasin. No published information about the subbasin's water budget has
been found, so any to attempt to predict how quickly the water would be replaced through
recharge would be speculative. It is known, however, that the importation of potable water
and the SCVWD controlled recharge program have assisted groundwater levels in the
subbasin to rise 200 feet during the last 40 years. Most of that rise has been in the surface
aquifer. The implication is that the subbasin is being recharged at a rate substantially higher
than the rate of withdrawal from all pumping, including dewatering for basement
construction. Consequently, it appears that the amount of flow from one, or even several,
dewatering operations would not have long-term effects on the surface aquifer.
In the areas adjacent to the site being dewatered, the rate and flow directions of the
groundwater would be altered temporarily by the dewatering process. Groundwater in the
influenced area would move toward the base of the excavation at a rate lower than the rate
of dewatering discharge. This effect could extend from several feet to several tens of feet
beyond the excavation depending on the method used, the level of the water table at the
time dewatering began, the permeability of the material adjacent to the excavation, and the
length of time the excavation needed-to be kept open and dry. Flow directions and rates
would revert to near normal when dewatering ceased.
There would be some displacement of groundwater flow around the newly constructed
basement, depending on the permeability of the surrounding soil materials. The volume of
space displaced by the basement could be several thousand to several tens of thousands of
cubic feet, which, although small compared to the volume of the surface aquifer, could be
significant locally, especially if there were other similarly sized basements in the immediate
vicinity. The flow of groundwater would readjust to this condition, possibly altering the
level of the water table in the vicinity of the site for several weeks or months, but is unlikely
to experience any major permanent change. The groundwater level in the surface aquifer
Page 5of7
ASSOCIATES
undergoes more significant changes during the rainy season than would be expected from
long-term flow deflection caused by basements.
Saltwater Intrusion and Subsidence
Saltwater intrusion and subsidence in the Santa Clara Subbasin are documented regional
effects of the excessive removal of groundwater from the deep aquifer ( overdrafting) over
many years. This practice was curtailed in the mid-1960s when the importation of potable
water increased substantially. Since then, the SCVWD has been recharging the subbasin
thereby raising groundwater levels, impeding saltwater infiltration of the surface aquifer,
and virtually eliminating further overdraft-related subsidence (the effects of previous
subsidence cannot be reversed because portions of the deep aquifer have been compressed
permanently). Such basin-wide effects could recur only if the deep aquifer became
overdrafted again. Because dewatering for basement construction occurs only in the
uppermost portion of the surface aquifer and involves only a small amount of groundwater
withdrawal, no effects would occur in the deep aquifer.
3. Palo Alto Public Works Department existing regulatory structure.
There are a number of policies in place that provide protection for the City's groundwater
resource and for property owners in the vicinity of new basement construction.
•
•
•
•
•
The Public Works Department prohibits the long-term pumping of groundwater
after a basement has been constructed. This eliminates the possibility that the
water table in the vicinity of the project would be lowered permanently.
The Public Works Department requires basements to be waterproofed and
strengthened structurally below the expected groundwater level. This eliminates
the need for groundwater pumping.
The Public Works Department requires permit applicants whose projects would
have basements to prepare a geotechnical investigation and report that would
determine, among other information, the expected highest groundwater level in
the local shallow aquifer. This allows the department to make informed
decisions about the advisability of basement construction at a particular site
and/ or to set the conditions under which basement construction may proceed.
If dewatering is necessary for basement construction, the Public Works
Department sets the dewatering permit conditions based on the hydrology of the
specific site under consideration. This ensures resource and property protection
where it is needed.
The Public Works Department allows the removal of seepage water that collects
along basement walls above the water table. Normally this removal would need
only a minimal amount of pumping, but may need to be monitored.
Page 6of7
attained the compliance threshold as indicated for the Covered Project type as set
forth in the Standards for Compliance outlined in Section 18.44.040.
(u) "Single-family or two-family residential" means a single detached dwelling unit or
two units in a single building.
(v) "Square footage," for the purposes of calculating commercial, multi-family
residential, and single-family and two-family new construction square ·footage, means
all new and replacement square footage, including basement areas (7 feet or greater in
height) and garages, except that unconditioned garage space shall only count as 50%
of that square footage. Areas demolished shall not be deducted from the total new
construction square footage.
(w) "Threshold Verification by LEED AP" means verification by a LEED accredited
professional certifying that each LEED checklist point listed was verified to meet the
requirements to achieve that· point. The LEED AP shall provide supporting
information from qualified professionals (e.g. civil engineer, electrical eng~neer, Title
24 consultant, commissioning agent, etc.) to certify compliance with each point on
the checklist. Documentation of construction consistent with building plans
calculated to achieve energy compliance is sufficient verification in lieu of post-
construction commissioning.
18.44.040 Standards for Compliance.
The City Council shall establish by resolution, and shall periodically review and update
as necessary, Green Building Standards for Compliance. The Standards for Compliance shall
include, but are not limited to, the following:
(a) The types of projects subject to regulation (Covered Projects);
(b) The green building rating system to be applied to the various types of projects;
( c) Minimum thresholds of compliance for various types of projects; and
( d) Timing and methods of verification of compliance with these regulations.
The Standards for Compliance shall be approved after recommendation from the Director
of Planning and Community Environment, who shall refer the Standards for recommendation by
the Architectural Review Board, prior to Council action.
18.44.050
(a)
080604 syn 6050410
Incentives for Compliance.
In addition to the required standards for compliance, the City Council may,
through ordinance or resolution, enact financial, permit review process, or zoning
incentives and/or award or recognition programs to further encourage higher
levels of green building compliance for a project.
6
ATTACHMENT F
18.12.090 Basements
Basements shall be permitted in areas that are not designated as special flood hazard areas as defined
in Chapter 16.52, and are subject to the following regulations:
(a) Permitted Basement Area
Basements may not extend beyond the building footprint and basements are not allowed
below any portion of a structure that extends into required setbacks, except to the extent that
the main residence is permitted to extend into the rear yard setback by other provisions of this
code.
(b) Inclusion as Gross Floor Area
Basements shall not be included in the calculation of gross floor area, provided that:
(1) basement area is not deemed to be habitable space, such as crawlspace; or
Ch. 18.12-Page 15 (Supp. No 13 -10/1/2007)
18.12.100 Regulations for the Single Story Overlay (S) Combining District
(D) the cumulative length ofany excavated area or portion thereof that extends into a
required side or rear yard does not exceed 15 feet;
(E) the owner provides satisfactory evidence to the planning director prior to issuance of
a building permit that any features or portions of features that extend into a required
side or rear yard will not be harmful to any mature trees on the subject property or on
abutting properties;
(F) such features have either a drainage system that meets the requirements of the public
works department or are substantially sheltered from the rain by a roof overhang or
canopy of a permanent nature;
(G) any roof overhang or canopy installed pursua~t to subsection (F) is within and is
counted toward the site coverage requirements established in Section 18.12.040;
(H) such areas are architecturally compatible with the residence; and
(I) such areas are screened to off-site views by means oflandscaping and/or fencing as
determined appropriate by the planning director.
(Ord. 4869 § 14 (Exh. A [part]), 2005)
18.12.090 Basements
(2) basement area is deemed to be habitable space but the :finished level of the first floor
is no more than three feet above the grade around the perimeter of the building
foundation.
Basement space used as a second dwe~g unit or portion thereof shall be counted as floor
area for the purpose of calculating the maximum size of the unit (but may be excluded from
calculations of floor area for the total site). This provision is intended to assure that second
units are subordinate in size to the main dwelling and to preclude the development of duplex
zoning on the site.
( c) Lightwells, Stairwells, Below Grade Patios and other Excavated Features
(1) Lightwells, stairwells, and similar excavated features along the perimeter of the
basement shall not affect the measurement of grade for the purposes of determining
gross floor area, provided that the following criteria are met:
(A) such features are not located in the front of the building;
(B) such features shall not exceed 3 feet in width;
(C) the cumulative length ofall such features does not exceed 30% of the perimeter of the
basement;
(D) such features do not extend more than 3 feet into a required side yard nor more than 4
feet into a required rear yard, but where a side yard is less than 6 feet in width, the
features shall not encroach closer than 3 feet from the adjacent side property line;
(E) the cumulative length of any features or portions of features that extend into a
required side or rear yard does not exceed 15 feet in length;
(F) the owner provides satisfactory evidence to the planning division prior to issuance of
a building permit that any features or portions of features that extend into a required
side or rear yard will not be harmful to any mature trees on the subject property or on
abutting properties; and
(G) such features have either a drainage system that meets the requirements of the public
works department or are substantially sheltered from the rain by a roof overhang or
canopy of a permanent nature.
(2) Below-grade patios, sunken gardens, or similar excavated areas along the perimeter of
the basement that exceed the dimensions set forth in subsection (1), are permitted and
shall not affect the measurement of grade for the purposes of determining gross floor
area, provided that:
(A) such areas are not located in the front of the building;
(B) all such areas combined do not exceed 2% of the area of the lot or 200 square feet,
whichever is greater; that each such area does not exceed 200 square feet; and that
each such area is separated from another by a distance of at least 10 feet. Area
devoted to required stairway access shall not be included in the 200 square foot
limitation.
( C) such features do not extend more than 2 feet into a required side yard nor more than 4
feet into a required rear yard;
(Supp. No 13 -10/1/2007) Ch. 18.12-Page 16
ATTACHMENT H
May 8, 2008
Steve Broadbent
575 Washington Ave
Palo Alto, CA 94301-4046
steve.broadbent@hp.com
(650) 521-3958
Honorable Mayor Larry Klein and Council Members
City of Palo Alto
250 Hamilton Ave
Palo Alto, CA 94301
Via email
Re: Green Building Ordinance -Request to Prohibit Basement Construction
Honorable Mayor Klein and Council Members:
I urge City Council to strengthen City ordinances to prohibit the construction of
residential basements, especially basements which require dewatering during
construction.
The mechanical removal of millions of gallons of groundwater from a construction site
has detrimental environmental impacts, and it is disingenuous for a construction project
to be considered "green" when it builds a basement in an aquifer. One so called "green"
project in Old Palo Alto pulled an estimated 100,000 gallons of water per day from our
underground aquifer for a period of 6 months. The Green Building Ordinance under
consideration by the City Council does not adequately address this abhorrent practice,
and you should amend the ordinance to prohibit basement construction.
The Planning & Transportation Division Staff Report for the April 9, 2008, study session
on the proposed Green Building Criteria for Private Development recognized basement
construction as an issue needing further scrutiny, but staff has failed to pursue
satisfactory resolution:
"The Commission and the public asked several questions about basements,
including a) groundwater discharged, b) the effects of dewatering on groundwater
and potential toxic plumes, c) the amount of concrete used, and d) impact on
trees.
"The Public Works Department has, in the past few years, revised its basement
policy to prohibit dewatering basements after construction. Dewatering from
basements during construction is still allowed ...
Green Building Ordinance -Request to Prohibit Basement Construction Page 1of5
"During the Zoning Ordinance Update, staff commissioned EIP Associates to
study the impacts of extensive basement construction on groundwater ...
"Staff believes that the use of basements deserves continued scrutiny ... Planning
has included provision in the green building criteria that larger homes (including
basement floor area) must achieve a greater number of green point credits than
smaller homes to help compensate for these resource impacts. Other approaches
would require extensive discussion as to when or whether to continue to allow
basements ... In recent ordinance discussions, this issue was broached but not
pursued."
I agree with staff that the use of basements deserves continued scrutiny, but I am
disappointed that staff believes green point credits can mitigate the serious impacts
basement construction has on our city. Public Works has attempted to dismiss concerns
raised by many residents by declaring the impacts as "negligible" or by disavowing
specific knowledge. A response that "staff is not aware" should not be considered
closure on the issues raised.
I take exception to a number of the conclusions put forth by Public Works, and I ask that
Council direct staff to reconsider their findings, including but not limited to:
•
•
•
•
•
Impact to neighboring properties
Land subsidence
Impact on trees and landscaping
Waste of water
Other detrimental impacts
Impact to Neighboring Properties
Staff asserts "the study concluded that the impacts of basement construction were
negligible on the groundwater system and on the groundwater on neighboring sites."
However, the EIP study clearly stated that
"In the areas adjacent to the site being dewatered, the rate and flow directions of
the groundwater would be altered temporarily by the dewatering process.
Groundwater in the influenced area would move toward the base of the
excavation ... This effect could extend from several feet to several tens of feet
beyond the excavation."
My concern is not with the long term impact on the broader Santa Clara Valley
groundwater system. My issue is with the site-specific impacts on neighboring properties
and the local community. You should not allow macro responses to obscure the micro
view of real damage that residential basements cause.
There may be no discernable long-term effect on the broader surface aquifer beneath the
Santa Clara Plain (macro view), but the prolonged extraction of groundwater from 2164
Green Building Ordinance -Request to Prohibit Basement Construction
Webster Street most certainly sucked the groundwater from underneath neighboring
properties, including mine (micro view).
Although small compared to the volume of the surface aquifer (macro view), the volume
of space displaced by a basement could be several tens of thousands of cubic feet which
would displace groundwater flow around a newly constructed basement. This could be
significant locally (micro view), especially if there were other similarly sized basements
in the immediate vicinity (refer to EIP study, page 5). Several residents have horror
stories of how the utility basements in their established homes began flooding after the
construction of neighboring basements.
The Foundation Engineering Handbook, by Hsai-Yang Fang (1991), confirms that" ... the
process of dewatering can have side-effects that are harmful to the project under
construction, the other facilities nearby, or to the environment ... Improper dewatering ...
can cause damage to the structures being built or to adjacent structures."
Land Subsidence
It is well established that subsidence can occur with groundwater extraction, and the
effects of subsidence cannot be reversed where portions of the aquifer have been
compressed.
"Saltwater intrusion and subsidence in the Santa Clara Subbasin are documented
regional effects of the excessive removal of groundwater from the deep aquifer
over many years ... the SCVWD has been recharging the subbasin [with potable
water] thereby raising groundwater level ... and virtually eliminating further
overdraft-related subsidence. Such basin-wide effects could recur only if the deep
aquifer became overdrafted again. Because dewatering for basement construction
occurs only in the uppermost portion of the surface aquifer and involves only a
small amount of groundwater withdraw! [relative to the broader Santa Clara
Subbasin], no effects would occur in the deep aquifer." (macro view, refer to EIP
study, page 6)
Take that "macro view" and bring it up to the surface aquifer underlying my home. My
"micro view" is that the drawdown of the groundwater under adjacent properties can and
does cause localized subsidence depending on the soil properties in the area. After 7 5
years, my home shouldn't be "settling" any more, but cracks in the plaster and cracks in
the pavement developed during the extended dewatering at 2164 Webster.
Fang confirms that "ground settlement can occasionally be a problem. Lowering the
water table increases the effective stress in the soil. The stress increase is usually modest,
and most soils are not affected significantly. But if there are compressible soils in the
vicinity ... settlement may occur. Whether the settlement causes significant damage
depends on the thickness and consolidation characteristics of the compressible deposit,
the depth of drawdown and the duration of pumping, the foundations of the structures
within the zone affected, and the type of their construction."
Green Building Ordinance -Request to Prohibit Basement Construction Page 3of5
Impact on Trees and Landscaping
Not only do I disagree with the Planning Arborist's assertion that "the localized
drawdown of the water table during dewatering does not impact trees as their roots do not
typically extend to that depth," the EIP study contradicts that assertion:
"The possibility exists th'lt adjacent landscaping could experience deterioration
from reduced groundwater availability." (refer to EIP study, page 4)
Fang also confirms that, "trees ·or other plantings in urban parks may be affected [by
dewatering]." Regardless of ~hether tree roots extend into the aquifer or not, the strong
pull of drawdown wells during a dewatering operation accelerates the percolation of
surface waters and induces drought-like conditions as the soil dries out. Landscape
irrigation cannot and should not be considered sufficient mitigation of the drought-like
stress inflicted on trees during prolonged dewatering.
Waste of Water
The City has been studying the use of recycled water for landscape irrigation and other
non-potable uses, and a multimillion dollar recycled water project is being considered.
The City clearly recognizes the need for water conservation, yet it permits the intentional
discharge of millions of gallons of water into our storm drains. That simply doesn't make
sense.
Public Works has stated that the water pumped from the shallow aquifers typically goes
into the storm drain system and then into the creeks, some of which are "losing" creeks,
meaning they lose their water back to the shallow aquifers. Public Works asserts that the
water is pumped out of the aquifer and then added back to it. But Public Works fails to
acknowledge that there are no "losing" creeks in my neighborhood, only engineered
channels.
• Adobe is all concrete bottom and sides from Hwy 101 to Alma.
• Matadero is all concrete bottom and sides from Hwy 101 to Alma, except from
Greerto hwy 101
• Barron is all concrete bottom and sides from Hwy 101 to Alma except for about
800 feet just upstream of hwy 101.
Concrete channels are not "losing" creeks, and since the natural aquifer flow is from the
foothills to the bay, any recharge in the short sections near Hwy 101 does not repleni'Sh
the impacted neighborhood.
Green Building Ordinance -Request to Prohibit Basement Construction Page4 of5
Other Detrimental Impacts
In addition to the unnecessary waste of water, the large volume of water pumped into our
storm drains could rupture our aging storm drains, damage streets and underground
utilities, and cause a sinkhole to develop.
Fang also notes that groundwater in the vicinity of a dewatering operation may be
affected "by temporary reduction in the yield of supply wells, by salt water intrusion, or
by the expansion of contaminant plumes."
Call for Action
Mayor Klein and Council Members, I call upon you to take action to restrict residential
. basement construction and stop the destructive practice of de watering. Palo Alto wants
to be a leader in the Green Building movement. Please amend the Green Building
Ordinance to prohibit residential basement construction in Palo Alto.
Sincerely,
Steve Broadbent
Green Building Ordinance -Request to Prohibit Basement Construction Page 5 of 5
Attachment I
To: Palo Alto City Council & Planning & Transportation// Re: Dewatering and Basement Construction// Date: July 19, 2008
Honorable Council and Planning and Transportation Committee Members:
I am writing to express my concerns about dewatering and basement construction in Palo
Alto. I am a professional scientist who has specialized in groundwater hydrology since
1975. I have a BS in Geology from Dickinson College and MS and PhD degrees in
Hydrology from Stanford University. I have lived in Palo Alto for 31 years. The
following statements are my personal views as a resident.
I recently received a call from another Palo Alto resident who purchased an older home
near property that was being outfitted with a new house. Excavation for the new home's
basement required pumping over 18-million gallons of groundwater 35 feet to land
surface, where the water was discarded into the City's storm sewer. According to the
caller, this dewatering was carried out with the approval of the City, without the need for
a variance. The resident reported that dewatering volumes on the order of millions of
gallons have been produced in multiple instances in Palo Alto, as mega basements have
become popular.
I do not advocate a complete ban on basement construction. Nevertheless, it is clear that
large parts of the City are unsuitable for the sorts of basements being built. Projects that
require large-scale dewatering should not be allowed. The reasons are simple:
(1) Construction of finished (dry) space where any part of that space is below the water
table is not advisable and should rarely if ever be allowed. This is necessary not only to
protect the newly constructed space, but also to conserve energy and water resources and
to prevent overloading of the storm-sewer system. Building codes prohibit basements that
would be "subject to flooding." The maximum elevation of the water table during normal
rainy seasons, plus a reasonable safety margin, sets the limit for allowable subsurface
construction. The need for large-scale dewatering indicates that the structure being built
is subject to flooding by groundwater. It is not to anyone's advantage to build basements
in unsuitable locations. The City must uphold existing law.
(2) Extensive low-lying areas of Palo Alto have shallow water tables, rendering them
unsuitable for basements. These areas were prone to flooding prior to "reclamation"
projects that "channelized" the downstream reaches of creeks and diked off the Palo Alto
Baylands. Sea-level rise from global warming is underway. Sea-level rise will increase
water-table elevations in low-elevation areas of the City. Empirical projections based on
ICPP scenarios call for 0.5 to 1.4 meters (1.6 to 4.6 feet) of sea-level rise by 2100
( http://www.sciencemag .orgtcgitcontent1abstract131s1ss10/368). These projections are likely low
( http://www.sciencemag.org/cgi/co~tent/abstract/317/5841/1064).
(3) The cone-of-depression from construction dewatering involving extraction wells with
only a few feet of horizontal setback from adjoining properties will definitely extend
beneath the adjoining properties, with potentially harmful effects from desiccation and
differential settling. Palo Alto's soils are heavily textured "adobes" in which the dominant
minerals of the fine fraction are montmorillonitic (smectitic) clays. Smectitic clays swell
with wetting and shrink with drying. Although modem foundations are designed to avoid
1 of2
To: Palo Alto City Council & Planning & Transportation// Re: Dewatering and Basement Construction// Date: July 19, 2008
failure in soils that shrink and swell, older structures are vulnerable to harm. Dewatering
removes water from adjacent properties. It seems prudent to avoid situations where one
person's allow.ed dewatering can harm neighboring properties.
( 4) Wasteful consumption of City water resources is a serious issue. Eighteen million
gallons of water is about 24-thousand CCF (hundred cubic feet). If applied to a medium-
sized City park with 200,000 square feet of irrigated turf-roughly the size of the
Mitchell Park soccer fields-the depth of the applied water would be about 12 feet. This
represents one hundred weeks of irrigation-five years' worth at 20 irrigation weeks per
year. Virtually all water removed during construction ends up in the Bay via lined storm-
runoff conveyances. Virtually none of it recharges groundwater or soil moisture. Waste
on this scale is unconscionable.
( 5) The possibility of groundwater contaminants being captured by construction wells
poses risks at multiple locations throughout the City. As more commercial and industrial
areas are rezoned to residential uses, the number of risks increases. Many contaminant
plumes are mapped, but others are poorly characterized. Such risks additionally weigh
against construction dewatering.
In summary, basements must be restricted to areas that have adequately thick unsaturated
zones-not all areas of Palo Alto are suitable. Large-scale dewatering should not be
permitted. Preservation of property and avoidance of contaminant entrainment are
compelling reasons to reassess current practices. The public costs of construction
dewatering are unacceptably high. Groundwater is a City resource so precious that no one
should be permitted to squander it on grand scales.
Prudent restriction of dewatering and basement construction will protect all parties.
My only interest in this matter was a promise to a fellow Palo Altan-concerned by
groundwater impacts-to assess the situation and communicate my findings to you.
With best regards,
David A. Stonestrom
1000 S. California Ave.
Palo Alto, CA 94306
2 of2
ATTACHMENT J
Davldson%20Basement%20Excavatlon%20Photos.htm 9/15/08 5:55 PM
From: Williams, Curtis
Sent: Monday, September 15, 2008 5:55 PM
To: Williams, Curtis
Subject: FW: Basement Excavation Photos
from: Jodyldavidson@aol.com [mailto:Jodyldavidson@aol.com]
sent: Tuesday, April 22, 2008 6: 02 AM
To: Williams, Curtis
Cc: French, Amy
Subject: Basement Excavation Photos
Hi Curtis,
These are some photos to help explain what I meant when I was trying to explain that the underground footprint of
basements was too large.
On the smaller size lots, the builders often excavate closer to the allowed set backs.
Many often excavate right up to the lot line, and then the builders start putting in the concrete and rebar.
I have seen this many times.
People in adjacent homes have told me that they believe that the excavation has ruined the foundation of their homes.
Since the side yard is all concrete, there is no where for the water to flow, except laterally.
This causes flooding to neighboring homes. Additionally, there is simply not enough side yard to allow for planting, and the
rear set backs are really too small to allow for tree planting when the tree grows.
Basically, the homes on these lots are all home and no yard.
I hope that the city will consider reviewing their poli9ies on the allotted size of a new home on these smaller lots.
Allowing this building practice has caused a lot of disharmony within our community.
Many residents feared that their homes could actually fall into the adjacent excavation site, and in many cases they had to
pay for fencing to protect their property.
Many felt that the chain link fence was simply not enough protection when the builders excavate to the lot line.
Please remember that some of the adjacent older homes on the smaller lots may not have this 6 foot side allowance.
Regards,
Jody Davidson
file:// /S: {PLAN/ PLADIV /Cu rtis/Desktop%2 05.8.08 /Green /Basements/Davldson%20Basement%20Excavation%20Photos.htm Page 1of3
Green cement may set C02 fate in concrete
SFGale.mrn
Green cement may set C02 fate in concrete
Carrie Sturrock, Chronicle Staff Writer
Tuesday, September 2, 2008
(09-01) 19:18 PDT --Call him cement man.
~-__ -. _ r e
Attachment K
Back when Stanford Professor Brent Constantz was 27 he created a high-tech cement that
revolutionized bone fracture repair in hospitals worldwide. People who might have died from the
complications of breaking their hips lived. Fractured wrists became good as new.
Now, 22 years later, he wants to repair the world.
Constantz says he has invented a green cement that could eliminate the huge amounts of carbon
dioxide spewed into the atmosphere by the manufacturers of the everyday cement used in concrete
for buildings, roadways and bridges.
His vision of eliminating a large source of the world's greenhouse C0{-2} has gained traction with
both investors and environmentalists.
Already, venture capitalist Vinod Khosla is backing Constantz's company, the Calera Corp., which
has a pilot factory in Moss Landing (Monterey County) churning out cement in small batches.
And Carl Pope, executive director of the Sierra Club, says it could be "a game changer" if Constantz
can do it quickly, on a big scale and at a decent price.
"It changes the nature of the fight against global warming," said Pope, who has talked with
Constantz about his work.
That might sound like hyperbole, but the reality is that for every ton of ordinary cement, known as
Portland cement, a ton of air-polluting carbon dioxide is released during production. Worldwide,
2.5 billion tons of cement are manufactured each year, creating about 5 percent of the Earth's C0{-
2} emissions.
When Constantz learned about the high C0{-2} levels, he thought he could do better. After all, the
majority of his 60 patents have to do with medical cement.
He claims his new approach not only generates zero C0{-2} , but has an added benefit of reducing
the amount of C0{-2} power plants emit by sequestering it inside the cement.
http://www.sfgate.com/cgi-bin/article.cgi ?f=/c/a/2008/09/02/MNGD 129361.DTL&type=~ri... 9/4/2008
'\
Green cement may set C02 fate in concrete Page 2 of 5
To make traditional cement, limestone is heated to more than 1,000 degrees Celsius, which turns it
into lime -the principal ingredient in Portland cement -and C0{-2}, which is released into the air.
Constantz uses a different approach, the details of which remains secret pending publication of his
patent.
At his pilot factory, a former magnesium hydroxide facility that made metal for World War II
bombs, magnesium crunches underfoot as Constantz, wearing a pressed, blue button-down shirt
with rumpled shorts and sandals, outlines' how the process works.
He pointed to two enormous smokestacks billowing flue gases full of carbon dioxide next door at
Dynegy, one of the West's biggest.and cleanest power plants.
Constantz takes that exhaust gas and bubbles it through seawater pumped from across the
highway. The chemical process creates the key ingredient for his green cement and allows him to
sequester a half ton of carbon dioxide from the smokestacks in every ton of cement he makes.
Constantz believes his cement would tackle global warming on two fronts. It would eliminate the
need to heat limestone, which releases C0{-2}. And harmful emissions can be siphoned away from
power plants and locked into the cement.
The same process can also be used to make an alternative to aggregate -the sand and gravel -that
makes up concrete and asphalt, which would sequester even more carbon dioxide from power
plants.
"The beauty here is we're taking this old industrial polluti~g infrastructure and turning it into
something that will save the environment," Constantz said.
On a per-person basis, the United States is the world's worst C0{-2} polluter from all sources. But
according to the Netherlands Environmental Assessment Agency, China just surpassed the U.S. for
total carbon dioxide emissions.
China is expected to produce 47 percent of the world's 2.5 billion tons of cement this year,
Constantz said.
To power its new buildings and sustain its building boom, China constructs at least one coal-fired
power plant a week. Each one belches out enough C0{-2} to cancel the benefits of every hybrid on
U.S. roadways, said Constantz.
A C0{-2} molecule can travel from Beijing to San Francisco in less than a day through atmospheric
circulation, he said. So even with California mandating that C0{-2} emissions fall to 1990 levels by
2020, a crisis remains.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD129361.DTL&type=pri... 9/4/2008
Green cement may set C02 fate in concrete Page 3 of 5
"Carbon dioxide is a global problem, not a regional problem," he said.
As far as cost, Constantz estimates his cement would retail for $100 a ton versus roughly $no for
Portland.
The reason no one invented it before now, he said, is that pe~ple didn't truly understand the
dangers of C0{-2} until less than a decade ago.
Skeptics question product
He has skeptics.
Portland cement has a track record of more than 100 years, and any new material would have to get
incorporated into building codes, noted Rick Bohan, director of construction and manufacturing
technology for the Portland Cement Association in Skokie, Ill.
And Tom Pyle, a Caltrans engineer who serves on the cement subgroup of Gov. Arnold
Schwarzenegger's Climate Action Team, acknowledged that the technology is possible, but he still
wants to examine Constantz's cement.
"We hope they have a carbon-reducing viable construction material," he said. "They need to show
up with a bag of this so we can test it."
Constantz is confident he will prove himself. Initially, he proposes mixing his new invention with
Portland cement to ease a conservative industry into a new product. Concrete bigwigs have invited
him to speak about Calera cement at their annual World of Concrete in Las Vegas next February.
Power plant partnerships
Constantz envisions building cement factories next to power plants the world over. A team is
scouting out U.S. locations. While Dynegy has supplied Constantz with some flue gas, it hasn't
entered into a formal agreement.
"As we're looking into the future, we're very interested in technology that would help capture C0{-
2} from the flue gase~ and turn it into a product that offers a benefit," said Dynegy spokesman
David Byford.
It could be good for business. California has mandated emissions reductions. And Congress is
working on legislation that would allow high polluters to buy credits from those with low
emissions. Power plants would have a huge incentive to sequester their C0{-2} in cement.
But even if Constantz succeeds, the world would still need to do much more to fight C0{-2}
emissions, said Chris Field, director of the department of global ecology at the Carnegie Institution
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Green cement may set C02 fate in concrete Page 4 of 5
for Science at Stanford. "It's a big, long complicated game," he said. "As we develop each new
segment of the solution we need to embrace it and deploy it and work hard to develop the next
segment of the solution."
Coral basis of idea
Big ideas can form in haphazard ways. The one for bone cement began during a televised football
game, when Constantz read an osteoporosis article in the New England Journal of Medicine. Three
weeks later, as he studied a coral reef, it occurred to him he could maybe synthesize coral skeletons
in human bones.
His new cement mimics how coral reefs form, too. Coral uses the magnesium and calcium present
in seawater to create carbonates much as he's using C0{-2} and seawater to make carbonate.
This latest invention took 18 months to conceive and execute. He feels it's one of the most
important things he's ever done.
"Climate change is the largest challenge of our generation," he said.
Who is brent constantz?
Profession: An associate consulting professor in Stanford's department of geological and
environmental sciences and founder of the Calera Corp. Created and sold three other companies -
Norian Corp., Corazon Technologies Inc. and Skeletal Kinetics.
Education: UC Santa Barbara, bachelor's of science (1981); UC Santa Cruz, doctorate (1986)
Family: Married and father of four.
Pastime: Surfing and rock climbing.
Concrete facts about cement
2.5 billion tons of hydraulic cement is produced worldwide annually. Add sand and gravel and
that makes more than 9,000 million cubic yards of concrete. That's more than enough concrete
to pave an eight-lane highway from the Earth to the moon and back again -twice.
If you stayed on the planet, that same eight-lane highway would circle the Earth almost 40 times.
Source: Portland Cement Association
E-mail Carrie Sturrock at csturrock@sfchronicle.com.
http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD12936I.DTL
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New Aquifer Filling Station
Revised 5/26/2015
1
Attachment B
Piping System
•Arrange piping system to draw water from settling tank being careful to keep the inlet a minimum of 1-2 feet above the
bottom of the tank to avoid settlement residue.
2
Locate the Filling Station
•Filling station should be located at the property line outside of the construction fence.
•Try to locate the station in a place where parked vehicles will not prevent equipment from using it, i.e. on a corner, near at
the edge of a driveway, etc.
•The filling station should be accessible 24/7.
3
Filling System
•Piping runs from the settling tank to a pump capable of providing a minimum of 150-200 gpm.
•Outlet of pump runs to lockable box where a standpipe is constructed.
•Standpipe contains a valve and outlet fitted with a MALE 2 ½” NH threaded fitting (Fire Hydrant threads).
•Inside the box is also located a switched GFI outlet to which the pump is plugged into. When the switch is thrown, the
pump turns on. This switched outlet is connected to the construction site’s temporary power. The GFI power outlet may be
placed somewhere outside the box, however, the switch should be inside. An “in-use” cover must cover the switch/outlet.
•A hose with a male connection shall be stored in the box to allow the water to be used for dust control onsite and for filling
tanks without pre-attached hoses or fittings.
•A standard hose bibb shall be installed next to the box to allow for gravity-fed filling of smaller “neighbor containers”.
4
Plumbing Signage
•The piping outside of the property lines needs to comply with California Plumbing Code Section 603.5.11:
•Each outlet on the non-potable waterline shall have posted: “CAUTION: NONPOTABLE WATER, DO NOT DRINK.” This would
apply to the hose bibb utilized by neighbors for non-potable purposes. The CPC also requires that exposed portions of the
piping be properly identified to the satisfaction of the AHJ. CPC Section 601.2 provides identification for non-potable
systems within a building. Although the proposed work is not within a building, the method would adequately identify the
piping system.
•Section 601.2 Non-Potable Water System Identification
•The system shall have a yellow background and black uppercase letters, with the words “CAUTION: NONPOTABLE WATER,
DO NOT DRINK.” The required piping identification shall be every 20 feet. The sizing of this lettering should be per CPC Table
601.2.2.
•This ‘signage’ comes in the form of stickers and can be easily found online.
5
Fill Point and Discharge Signage
•The contractor shall provide a sign according to Public Works specifications and attach it to the outside of the fill station box.
•The contractor shall also provide signs to be mounted on a standard “A-frame” barricade to be placed at the dewatering
discharge point (usually a catch basin).
•Upon completion of dewatering activities, the signs shall be returned to the Public Works Inspector for recycling.
6
Water Station
Sign Specifications
•These specifications are provided as guidance to produce/order consistent signs:
•This sign is aluminum, 20.5” tall by 14” wide. The margin is 0.25” and the border is also 0.25” wide.
•“Water Filling Station” is 1.5” tall, Highway Series E font.
•“Suitable For Irrigation Purposes” is 0.75” tall, Highway Series B font.
•“Do Not Drink” is 1.2” tall, (font as it is part of the symbol). The red circle and slash has a circumference of
4.5”.
•The city logo is 4.2” tall by 2.2” wide.
•Mount this sign to the water station door.
7
Discharge Point
Sign Specifications
•These specifications are provided as guidance to produce/order consistent signs:
•This sign is aluminum, 24” tall by 24” wide. The margin is 0.375” and the border is 0.625” thick.
•“Non-Potable Water Discharge” is 2”tall, Highway Series C font.
•“Do Not Drink” is 1.2” tall, (font as it is part of the symbol). The red circle and slash has a circumference of
4.5”.
•“To Use This Water…” is 1” tall, Highway Series C font.
•The city logo is 4.2” tall by 2.2” wide.
•Mount this sign to each side of an A-frame barricade (2 signs total) and place it at the discharge point.
8
Log Sheets
•Copies of the following log sheets with a pen
shall be attached to the inside of the door of
the filling station.
•All users of the water filling station shall fill
out the form for each use.
9
Log Sheet: Available from Public Works
10
Instructions
•Attach a copy of operating instructions to the
inside of the box.
•Sample instructions:
11
Security
•Box should be sturdy and locked with a
combination lock.
•Provide the lock combination to Public Works
– Engineering Services.
12
Inspection
•NO DISCHARGE IS ALLOWED WITHOUT A DEWATERING PERMIT.
•Once there is groundwater in the settling tank, contact the Environmental
Compliance division at (650) 329-2122 or (650) 329-2430 to have the water tested.
•Public Works will contact you to inform you of the results.
•Once the station is constructed and ready to operate, contact Public Works
Inspection at (650) 496-6929 to schedule an inspection.
•Once the Inspector has approved of the station installation, Public Works -
Engineering Services can issue you the dewatering permit.
13
Important Notification
•Contractor shall notify Public Works –
Engineering Services ONE WEEK prior to
ending dewatering operations.
•This will allow City staff to adjust vehicle
operations and routes accordingly.
14
Final Notes
•The New Aquifer Filling Station is a quickly evolving program -
changes, modifications, revisions, and additional conditions,
policies, and equipment required may occur at any time.
•This handout is a living document and will be revised as the
program develops.
15
Questions?
•Contact:
Mike Nafziger, P.E.
Senior Engineer
Public Works – Engineering Services
(650) 617-3103
mike.nafziger@cityofpaloalto.org
Or,
Public Works – Engineering Services
(650) 329-2152
16
GROUNDWATER
PUMPING
HAPPENING
IN YOUR
NEIGHBORHOOD
A BASEMENT CONSTRUCTION PROJECT
in your neighborhood is pumping water
to a stormdrain which leads to a creek.
This groundwater cannot be used as
drinking water, but it can be pumped to
creeks or used for irrigation and dust
control. Creeks would ultimately receive
this same water if it was not pumped
there first. This water is important to the
creek and Bay ecosystems.
The construction project in your
neighborhood offers a residential filling
station to access some of this pumped
water for use on landscaping.
Visit cityofpaloalto.org/recycledwater or
call (650) 329-2151, Press option #8
for filling station locations and additional
information.
Attachment C
Updated and posted 8/11/15
Groundwater Pumping From Building Sites
Frequently Asked Questions
During this time of severe drought, our community is working hard to conserve
water. So when community members observe water pumping from construction
sites, they want to know what is happening. Here are answers and information to
help address the most frequently asked questions we have heard.
Q. What is the water that I see running into the storm drain from construction
sites?
A: During the construction of a basement or underground garage there is
sometimes a shallow upper groundwater aquifer that must be temporarily
pumped down to allow construction to move forward. This groundwater is not
the same water that would be used for drinking.
Q: Does the City regulate the pumping and discharge of this water?
A: The City permits the discharge of this water to either the storm drain or the
sanitary sewer, depending on the water quality. The water is sampled and tested
for cloudiness, salinity and acidity. Only very clear, high quality water can go to
the storm drain. Temporarily pumping this water is standard practice in areas
with groundwater closer to the surface to allow construction to proceed, and no
practical alternative has been found. Using the water for irrigation and dust
control is possible, and the owners and construction managers are strongly
encouraged to find uses for the water.
Q: Given the high quality of the water and the severity of the drought, why
does the City allow it to be “wasted” by discharging it into the storm drain
system?
A: The shallow water aquifer being pumped contributes to the flow of our creeks
and to the Bay. The groundwater is part of the water cycle for the Bay and
enhances the habitat and improves the quality of the creeks and lower South San
Attachment D
Updated and posted 8/11/15
Francisco Bay. When the shallow aquifer is pumped from basement construction
sites into storm drains, it travels a different path, but ends up in the same place:
the lower South Bay. So, the water is not wasted, but rather is used to improve
the Bay’s habitat and ecosystem, whichever pathway it takes.
Q: Can’t this water be used for other purposes?
A: The pumped water hasn’t been disinfected or sufficiently tested to drink or use
inside the home. Palo Alto‘s emergency drinking water wells tap into a much
lower and more protected aquifer. However, the pumped water could be used
for irrigation, dust control or similar uses. Palo Alto now requires that contractors
have the pumping system fitted with valves and connections so that City crews
and others can fill water trucks, street sweepers and other containers. For truck
fill stations, the water is tested for acidity and salinity. Private parties can also fill
trucks and containers. Such “fill-stations” are now in place at the Palo Alto active
basement construction pumping sites listed below:
1405 Harker
1820 Bret Harte
804 Fielding
713 Southampton
3832 Grove
2230 Louis
View our map of FREE Water Filling Stations.
The site owners and construction managers are encouraged to find more water
users, but this will continue to be a small fraction of the total pumped water.
Call 650-617-3103 for more information about accessing the fill stations.
The volume of water being pumped is large compared to pump truck capacities,
but is too small and too shallow to impact the very deep and very large Palo Alto
emergency ground water aquifer.
Updated and posted 8/11/15
Q. What happens after construction?
A: In recent years, Palo Alto has required that structures be built as water tight so
that groundwater flows around a building, rather than into it. But a number of
older buildings leak, and water is pumped out of the building basement/garage
into the storm drain or sanitary sewer. Palo Alto City Hall and 525 University are
two of the largest “dischargers”. We have looked at utilizing the water from City
Hall, but it has not proven to be cost effective. With new water restrictions in
place, this issue is being reexamined once again. However, the City Hall water
does go through the storm drain to San Francisquito Creek where it supports
habitat, including for fish, especially in the summer when there is no rainfall.
Q. What can I do if I see water being wasted?
A: The City has hired a part-time Water Waste Coordinator who is specifically
dedicated to drought response actions. Need to report a leak, runoff or waste?
We have many communications means for you! Please let us know!
Report water use incidents through the City’s PaloAlto311 web or mobile
app at cityofpaloalto.org/services/paloalto311/ or go visit to
www.cityofpaloalto.org/water to access the link directly.
Contact the City’s Water Waste Coordinator at 650-496-6968 or
Martin.Ricci@CityofPaloAlto.org - or -
Call Customer Service at (650) 329-2161 - or –
Email UtilitiesCommunications@CityofPaloAlto.org - or –
Call Utilities Emergency Dispatch at (650) 329-2579
1 10/5/2015
GROUNDWATER PUMPING FOR RESIDENTIAL BASEMENT CONSTRUCTION
Frequently Asked Questions
Save Palo Alto’s Groundwater, a Community Resource
Is groundwater pumped for residential basement construction?
Yes. Very large amounts of groundwater from the shallow surface aquifer are pumped to build
basements when below ground soils are saturated to provide dry soils using a commercial-scale
construction process termed “dewatering.” This technique is now being permitted for
constructing residential basements in Palo Alto at a rapidly increasing rate, from an average of
five (5) per year (2006 – 2008) to at least 14 this year. Dewatering is used only at those sites
with water saturated soils; it is not used at drier sites.
Why should I care about groundwater pumping for basement construction?
Aquifers and groundwater are a community and public trust resource that, although unseen,
play an important role literally supporting structures and infrastructure, draining storm water,
and storing and providing moisture for our canopy and plants.
What are the effects of removing groundwater?
Removing groundwater has a variety of impacts. The forces exerted by groundwater literally
support the ground, structures and infrastructure and through capillary action, provide water to
our trees.
The shallow surface aquifer pressure increases the recharge of the deeper aquifer which is used
for irrigation and on which Palo Alto relies for emergency water.
Lowering the water table locally causes ground settling. This settling may not be uniform across
structures, which may then develop either tight doors or windows, or permanent cracks in
foundations, walls or masonry. Settling of even less than an inch is adequate to cause
permanent structural damage. Lowering the water table below the seasonal normal fluctuation
can cause irreversible compression of the soil (hysteretic soil compaction).
What are the effects of lowering the water table on vegetation?
Water available for trees and plants is reduced. Soils wick water up, much like sponges,
resulting in increased soil moisture several feet above the water table, well into the root zones
of trees in much of the area in which dewatering is occurring.
What are the impacts of these basements after construction?
Both the City of Palo Alto and the Santa Clara Valley Water District provide incentives to install
permeable pavement to reduce the amount of storm water entering storm drains and instead
soak into the ground, thereby reducing flood risks and recharging aquifers.
Basements displace soils that would otherwise be available to absorb rain water, increasing the
probability that rain water will flow into the storm drains.
Attachment E: Correspondence
2 10/5/2015
Much of Palo Alto is known to have covered gravel beds from former creekbeds. Basements
are dams in the unseen rivers that flows through the soils, gravel beds and aquifer beneath Palo
Alto. Water needs to flow around these basements. If water cannot flow through the soil fast
enough, it will flow above the soil, into the storm drain system, and if the storm drain capacity
is exceeded, will flood our streets and properties.
The water table/water pressure surrounding a basement is locally higher, in the same manner
as water in a flowing river is higher as it flows around an obstacle. The locally higher water
table increases the risk that basements in neighboring properties will flood.
What can I do if my property is damaged by ground settling caused by groundwater
pumping?
You’re on your own. You must resolve any damage claims directly with the party that caused
the damage. The City will neither order the dewatering to stop nor help you with any damage
claims. You may sue. In that case it will be necessary for you to prove that the specific
dewatering operation was the cause of the damages, and most likely pay attorney’s fees, which
might be reimbursed if you obtain a judgement in your favor.
How much water is pumped?
In total, it is estimated that 126 million gallons (16,000,000 ft3) of groundwater has or will be
pumped out for the construction of 14 basements in Palo Alto in 2015 alone. This is enough to
cover a football field 275 feet deep, or fill 50,400 water tank (2,500 gallon) trucks, or provide
enough water for 18,000 average Palo Alto residences for the entire month of July, 2015
(equivalent to 40-50% of the state-mandated water conservation goal for all single family
residences in Palo Alto for a year) or lower the aquifer by more than 1 foot over an area of 1
square mile.
This estimate is based upon the midpoint of City’s estimate of 8 – 10 million gallons (1.2 million
cubic feet) per basement. For some basements, more than 20 million gallons is pumped. The
amount of water being pumped out is not metered.
Where is groundwater pumping occurring?
Most of the residential dewatering projects are concentrated in an area of approximately 1
square mile bounded by Webster Street, Louis Road, Colorado Avenue and Channing Avenue,
although two are near Middlefield Road further south.
From where is the water pumped?
Groundwater is typically pumped from 15 to 25 feet below grade, and the groundwater table
locally lowered about 2 feet below the bottom of the basement in the area to be excavated.
The “bottom” of the basement is generally 10 – 20 feet below grade; some are below sea level.
Groundwater is typically pumped at a rate of 50 – 100 gallons per minute continuously for 3 – 6
months.
3 10/5/2015
How much do government agencies collect in fees and permits for construction dewatering?
The City of Palo charges approximately $710 for a dewatering permit for 6 months.
There is no usage-based fee or assessment for discharging the groundwater pumped out for
construction into the storm drain. The total cost to the developer for removing this resource
from our aquifer is about $710.
How much do residents pay for equivalent water disposal in the storm drain?
The Storm Drain Fee for 1 equivalent residential unit (ERU) is $12.63 / month ($151.56 / year).
A single dewatering site will dump as much water down the storm drains as the city estimates
would go into the storm drains from 480 residences (1 ERU / residence) in a year. Developers
are not currently required to pay any additional fees to compensate for the heavy use of the
city’s storm drains, even though a “fair share” payment would be $72,748 for a typical
basement.
How much would Santa Clara Valley Water District charge for a resident to pump non-potable
groundwater for irrigation?
Santa Clara Valley Water District charges about $600 / acre-foot (43,560 ft3) for a permit to
pump groundwater. For the amount of water pumped for a typical basement, the cost would
be approximately $16,500. However, a specific exemption from fees is provided for
construction dewatering in the shallow aquifer. The fee to builders is zero.
Is this groundwater pumping sustainable?
The amount of water removed from the aquifer in 2015 is roughly the same as would be
available to recharge the aquifer from average (not drought) rainfall for one year, after allowing
for runoff and evaporation over an area of 1 square mile.
What happens to the pumped groundwater?
Approximately 99% is dumped into the storm drains, which then flows to the Bay.
Isn’t this pumped water available for irrigation for free?
The City requires faucets with hose connections and fill stations for water tank trunks at each
dewatering site. There are no requirements for the actual use of the water or the pressure
supplied to hose connections for neighborhood use; City policy effectively condones wasting
water. In practice, the water is not substantially used. Although the water is of high quality
and usable, it is wasted.
How and when is the shallow surface groundwater replenished?
Primarily from rain and landscape irrigation. Precise recharge rates are not known, but it is
believed to be in the range of months to years.
Doesn’t the water flow to the Bay anyway, and therefore doesn’t pumping the groundwater
improve the environment of the Bay?
The aquifer and soils have an important role in transporting storm water to the Bay; more
water flows in the unseen river beneath our homes to the Bay over the course of a year than
4 10/5/2015
down the creeks. However, during the summer, there is little flow in the aquifer (there almost
no flow in creeks either). Dewatering locally lowers the water table below its normal historical
low level, and in some cases below sea level, much as pumping water from a lake could lower
the lake level below the outlet level.
Hasn’t the City already carefully studied dewatering?
The City commissioned a study in 2004, and City staff reviewed the study in 2008 after receiving
citizen complaints. Not only are several important issues not addressed, especially related to
local effects, there are important differences between the current situation and the time of the
original study. Existing City dewatering policy does not anticipate the current number or water
volume of dewatering activities within the City. Despite acknowledgment by the study that
there will be “temporary and local effects,” the study does not meaningfully address localized
impacts, including ground settling, reduced soil moisture for trees, flood risks and storm water
management, public compensation for the use of the water, or public policy in an era of climate
change. Furthermore, it is incorrectly assumed that short-term effects will not cause
permanent damage.
From where did this information come?
All information in this document is either provided by or derived from the City of Palo Alto, the
Santa Clara Valley Water District, USGS topographical maps, the US National Oceanographic
and Atmospheric Administration, and materials provided by degreed professionals in soil
sciences or hydrology, including documents in the Public Record for the City of Palo Alto.
What is the objective of Save Palo Alto’s Groundwater?
Palo Alto’s groundwater is a community resource too valuable to freely pump and dump down
storm drains simply for the construction of residential basements. We are requesting that the
City of Palo Alto enact an immediate moratorium on new permits for the pumping out of our
groundwater (“dewatering”) for the construction of residential basements in Palo Alto to
further study the effects of dewatering. Dewatering should only be permitted if the study
shows negligible impacts, including effects on storm water management and flood risks, and
policy is updated to require minimization and complete mitigation of all impacts including
requiring full use of the pumped water, payment for use of infrastructure and resources,
protection of infrastructures, properties, and the canopy, with all costs to be assumed by the
developing party.
Is a more detailed document available?
Yes, a White Paper including references is available upon request.
How do I obtain further information or help with this effort?
Send an e-mail with your name and contact information to
PAgroundwater@luxsci.net
Questions related to the City of Palo Alto policies on permitting the
pumping of groundwater for the construction of residential
basements
Keith Bennett
8/11/2015
Background: My concerns relate to the documented local and transient impacts of new basements and
their construction, as well as the permanent impacts of new, large basements on the capability of local
soils to handle rainwater during periods of heavy rain, such as has been experienced in 1982 and 1998.
My primary concern is not the apparent “waste” of a groundwater resource during a drought (although
the amount of water pumped for basement construction is about 10% of the total 24% conservation
goal for the City, and report indicates that the surface aquifer being pumped has partly been
replenished by imported water from the Delta). Aside from considerations of water quality, I am aware
that City has far more water that could be used for irrigation (aside from delivery cost) available from
the Water Treatment Plan
I have read the 2004 report by EIP, as well as the Staff Report from Curtis Williams dated 9/24/2008.
From my reading of these reports, they do not support the conclusions that dewatering on the current
scale in Palo Alto is not without significant adverse effects.
1. My understanding is that the two documents listed above, plus soils reports generated from the
construction of new buildings, especially buildings with basements are the primary bases for City
Policies. The City has prepared a map showing groundwater depth based upon measurements
related to construction. This map is available in electronic format. The soils reports from new
construction are copyrighted, and may be viewed, but may not be copied. I assume, however,
that the City could, if desired, use the information in the soils reports for analysis and modelling
purposes.
Is my understanding correct and substantially complete?
2. Importance of recharge rates and source on the overall impacts of dewatering on the shallow
aquifer. Long term impacts are only negligible if they aren’t offset by recharge.
The 2004 Report primarily focuses on the impact on the level of the entire Santa Clara Subbasin
surface aquifer, and simply assumes that the water pumped in a year will recharge the next year.
Shouldn't the basis for policy consider not only the fraction of the total available aquifer
pumped, but also critically consider recharge?
The report states the following:
a. There are 5 – 10 basements / year constructed with dewatering in Palo Alto, and as the
aquifer extends beyond Palo Alto, and other cities may also pump groundwater, the
total impacts on the aquifer would be far more significant. It would appear that
annually >1% of the aquifer / year or 10% per decade could be depleted. This is not
insignificant. To avoid long-term effects, the groundwater must be recharged.
b. The subsurface aquifer has been significantly recharged by IMPORTED (i.e. purchased)
water (Pg 6, see above):
“It is known, however, that the importation of potable water and the SCVWD controlled
recharge program have assisted groundwater levels in the subbasin to rise 200 feet in
the last 40 years. Most of the rise has been in the surface aquifer.”
Note: it is the surface aquifer that is being depleted for dewatering.
A January, 2015 document from the SCVWD “Where does our water come from?”
(attached) lists three primary sources for groundwater replenishment: “3. Water
importation from the Delta, which the district also releases to creeks and recharge
ponds for managed groundwater recharge.”
Should Palo Alto have a policy that accelerates sending of water to the Bay through
groundwater pumping in a drought when replacement supplies are restricted, and
furthermore, it appears from public documents that some of the water being pumped
for basement construction may, in fact, may in fact be due to SCVWD groundwater
recharge programs?
Is it reasonable that those dewatering be permitted to use this resource without
compensation based upon consumption, i.e. shouldn’t the dewatering amount be
metered and charged for example to pay SCVWD for replacement water?
3. Local Effects
The EIP report does not provide any basis to support the statement (Pg. 5) regarding the
geographical extent of local lowering of the groundwater, and provides no information on the
volume profile of the dewatering:
a. Assuming a dewatering of 1,000,000 ft3, well below the 7,000,000 ft3 mentioned as
typical in the report, but comparable to the lower end of the pumping rates and
durations mentioned in the City Staff report corresponds to a volume of 500 x 500 x 8
feet, assuming 50% porosity of the soil. It is clear that some effects must extend well
beyond “several tens of feet.” It is also clear that the extent of dewatering must depend
upon local soil composition, the depth of pumping and the time (and rate) that the
water is removed.
b. The 2004 states “local settlement on the order of fractions of an inch could occur.” (pg
7.) Settlement (either temporary or permanent) of even fractions of an inch is adequate
to break windows, cause cracks in masonry and plaster, or require doors to be reworked
to open and close properly. There is no guarantee that settling will be perfectly level
across a nearby property, which is likely the case if a gradient is created in the soil
moisture content. Furthermore, the dewatering may extend below the depth of
normal “seasonal” water table variation and therefore may affect the supporting
capacity of soils between the dewatering depth and the normal “low level” of seasonal
water table fluctuation.
Reports by homeowners (including the letter in the 2008 Staff Report from the resident
at 575 Washington), myself of home damage and a broken water main on N. California
several hundred away from, but particularly correlated in time with dewatering events.
Could these events provide evidence that dewatering is, in fact, causing at least
temporary settlement large enough to affect infrastructure and homes, and that the
extent may be further than assumed?
c. There is no discussion on the impacts of dewatering on soil moisture (used by plants)
above the aquifer. The Santa Clara County Water District leaflet compares soils to a
sponge:
The relevant question is the extent to which dewatering reduces soil moisture in the
surrounding area not whether or not tree or plant roots are below the water level of
the aquifer (generally, plants desire moist, but not saturated soils, as they need air,
therefore the roots of land plants are generally not in saturated soils. Like sponges, soils
wick water upwards from the aquifer. Is soil moisture unchanged above the aquifer
when the water table is locally and temporarily lowered? It is important to consider
the effects of dewatering in the spring, when soil moisture and the water table are both
higher. Isn’t reducing soil moisture earlier in the year in the root zone of plants is more
or less equivalent to an artificial drought?
Of course, it is possible to compensate for lower soil moisture by watering plants more,
however this is quite expensive during conditions such as the current drought, and
furthermore the expense is borne by the affected homeowners and city plants (e.g.
trees). If dewatering does increase the need for supplemental watering, then, isn’t
dewatering in practice indirectly increasing demand for potable water (as it’s 1/10th the
price of recycled water).
4. Long term impacts of basements on flooding risks during storms
A simple analysis shows that basements extending into a zone of saturated soil (once
constructed) will significantly and negatively affect the ability of local soils to hold and drain
rainwater during heavy storms, with increased risks of flooding, either in neighboring homes
and in wider areas.
a. The construction of basement means that there is no soil in the removed volume to
absorb rainwater. As basement and lightwell can cover 35% of the lot, and any
basement that requires dewatering for construction by definition extends to saturated
soils, the local reduction in the capacity of soils to hold rainwater is significant. The
result is a locally higher water table / water pressure, at least temporarily until the
water can drain. The locally higher water table increases the risk that neighboring
properties, especially those with older basements will flood.
The 2008 letter from the resident of 575 Washington mentioned the same concern.
Complications of basement flooding can be significant. In 1998, basement flooding
triggered a fire at 595 N. California (a pilot light was extinguished by the water; the
escaped gas then exploded when lit by a different pilot light). Additionally many
basements of older homes were flooded. Basements only rarely flood.
During the 1998 storm, the saturated water line along Webster St. near N. California
was about 3- 4’ below street grade, indicating that there is no significant extra capacity
in the soils, at least in some parts of the city. It is likely that soils were saturated closer
to the surface in lower areas.
If the soils become saturated to the surface, rainwater will no longer be absorbed and
instead will flow into the storm drains. If the storm drains cannot handle the additional
water, localized street flooding will occur.
The City provides rebates for the use of permeable paving materials to reduce the load
on the storm drains. This assumes that the soils can absorb the water and release it
more slowly.
Is the construction of large (and deep) basements in areas that have risk of soil
saturation above the basement level consistent with this policy?
Is a policy that increases the risk of flooding wise? Is it appropriate for Green Building
Certifications?
b. Basements are like dams in the unseen river through the soils (and aquifer) beneath
Palo Alto, and impede the discharge of water during periods of heavy rain, increasing
the level of saturated soils, and the risks of flooding. We would not think of blocking
any creek, yet basements are doing so for the channel that carries the most water to the
Bay.
i. The soils and aquifer under Palo Alto surely carry significantly more water to the
Bay than San Francisquito Creek over the course of a year. This can be easily be
shown by calculating the volume of water in even 12” of annual rainfall that falls
on the area (about 3.3 x 1.8 miles) of Palo Alto between El Camino and San
Francisco Bay and comparing the annual volume of water to that which flows in
San Francisquito Creek. In addition, the soils and aquifer must carry water from
lands west of El Camino, including Stanford and the foothills.
ii. The potential of basements to block aquifer / soil water flows is very significant.
Basements are now quite large (perhaps covering ½ of the property width) and
a very large fraction of new construction (~70% in permitted areas) includes
finished basements.
Have the impacts of basements on the capacity of our soils to handle
rainwater during heavy storms been properly considered?
From: Leah Rogers [mailto:leah.rogers@stanfordalumni.org]
Sent: Monday, October 26, 2015 6:38 PM To: Council, City; Keith Bennett Subject: re: Per request of Greg Schmid during Oral Comments at the Oct 5 2015 City Council Meeting Dear All:
Below is my effort to put in writing what I said in the Oral Comments period of the October 5
2015 City Council Meeting. I have also included some references at the request of Greg Schmid. Thanks you for your time and listening to these thoughts about the dewatering issue. Sincerely, Dr. Leah Rogers
(Ph.D. from Stanford in Hydrogeology)
The 2004 EIP report suggests the range of influence on the
water table aquifer is on the order of tens of feet from the
dewatering well. The amount of water table drawdown
necessary in construction of basements in Palo Alto is
approximately 15 feet (i.e. drawing down the water table from
10 ft below ground surface to 25 ft below ground surface. If we
consider standard calculations of radial flow applications of
Darcy’s Law (Freeze and Cherry, 1979 (note Eq 8:12-8:15);
Manning, 1997; Bennett et al., 1990), a lowering of the water
table level approximately 15 feet an unconfined aquifer in
alluvial deposits may create a cone of depression that spreads
out towards a few hundred feet in any direction. This assumes
some general hydraulic conductivities and other aquifer
parameters that could be in alluvial deposits in this area. Note
regional studies suggest hydraulic conductivity values may
range between 260 and 6000 gpd/ft2 (McCloskey and
Finnemore, 1996). There are many major factors that influence
the drawdown of the water table: thickness of the water table
aquifer, interfingering of layers that may inhibit flow (aquitards
in which case coefficients would have to be assumed to account
for leaky aquifers), and whether or not steady-state is reached.
Precise predictive modeling would require to collection of data
from time dependent well testing. However, we may say
qualitatively where there were more sands and gravels the cone
of depression would reach further than if there were tighter silts
and clays.
When several of these projects going on in the same
neighborhood, which is the case in Palo Alto, cones of
depression may interact cumulatively. As the dewatering effect
from multiple projects are cumulative and interact with reduced
irrigation, it is difficult to assign “responsibility” for damages to
property or landscaping to specific dewatering projects.
The drying out of soils is often not perfectly reversible. This is
called hysteretic soil compaction. For example, wet clay worked
into a dry piece of pottery cannot simply be put back into it’s
original state by submerging it in water. Imagine over a 3-4
month dewatering project that particularly the interfingering
clays in the subsurface will cause unequal rewetting. It is quite
plausible that the scale of these dewatering projects are
responsible for the additional cracks in walls and foundations
which neighbors in the area have noted. For example, the 2008
City Manager’s Report includes a letter from Steve Broadbent
raising such issues.
Overall, it would seem that the City of Palo Alto would do well
to require dewatering projects to provide specific
characterization and predictions of groundwater impact during
the course of the proposed project before approving any
dewatering especially in times of drought and water-
conservation. Even better would be adoption of construction
practices and project designs that significantly reduce the need
for dewatering, especially considering reduced irrigation in the
area during droughts.
References:
Bennett, Gordon D., Thomas E. Reilly, and Mary C. Hill. 1990.
Technical Training Notes in Ground-Water Hydrology; Radial
Flow to a Well. US. Geological Survey Water Resources
Investigations Report 89 4134.
http://pubs.usgs.gov/wri/1989/4134/report.pdf.
Freeze, R.A. and J. A Cherry. 1979. Groundwater. Prentice Hall
Inc., Englewood Cliffs, NJ. 604 pp.
Manning, J.C. 1997. Applied Principles of Hydrology. Prentice
Hall, third edition, 276p.
McCloskey, T.F. and E. J. Finnemore. 1996. Estimating
Hydraulic Conductivities in an Alluvial Basin from Sediment
Facies Models. Ground Water, Vol. 34, No. 6 November-
December 1996. http://info.ngwa.org/gwol/pdf/962962189.PDF.
On Wed, Jul 15, 2015 at 4:18 PM, Bobel, Phil <Phil.Bobel@cityofpaloalto.org> wrote:
Ms. Relman:
Our Assistant City Manager, Ed Shikada has asked me to respond to your 7/14 email about the
pumping of groundwater to allow the construction of basements.
A number of residents have raised issues very similar to yours, and we have created a website
to address them: Recycled Water Web Page . Scroll down to the last line and click on “here” to
see our “Frequently Asked Questions” about the pumped ground water.
While I know it appears to be wasting water, the shallow ground water aquifer is flowing to our
creeks and Bay. The pumping and discharge of this shallow ground water to the storm drains
sends the ground water to the same place, our creeks and Bay, where it supports ecosystems
and their wildlife. Nonetheless, the City is working with builders to try to get as much of water
used as practical. The main limitations are the very high cost of trucking the water and the lack
of a piping system from the pumping sites. Farmers are just too far away to make their using it
practical at this time. A portion of the water is being used to water City trees, provide dust
control at construction sites, and similar non-potable uses.
With respect to the potential for drawing down the shallow groundwater and causing land
subsidence, we do not have reason to believe this would occur, given the short duration
pumping and the small number of wells involved here. Subsidence can occur when pumping
happens over a number of years from many wells.
I hope this helps address your concerns.
Phil Bobel
Assistant Director, Public Works
From: Shikada, Ed Sent: Wednesday, July 15, 2015 8:07 AM To: Georgia Relman Cc: Council, City; Bobel, Phil Subject: Re: draining ground water
Dear Ms. Relman,
Thanks for contacting us with your concerns. I will ask Public Works staff to review the issue
and reply directly to you. There has been quite a bit of activity on this issue recently that may
interest you, specifically on the topics you raised. You may also wish to participate in future
discussions.
Sincerely,
Ed Shikada
Assistant City Manager
On Jul 14, 2015, at 4:12 PM, Georgia Relman <georgiarelman@gmail.com> wrote:
Hi All,
I have a question. Just in our neighborhood alone (around professorville), 4 construction sites
building private homes are draining ground water at full blast down storm drains; this has been
going on for many MONTHS now.
Why are private construction companies allowed to drain Palo Alto ground water? Wouldn't it be of benefit to use this water for Palo Alto parks etc. or sell it to farmers for Palo Alto profit
(because it is needed)?
When the ground water is drained under Palo Alto, will the ground sink as it has in other areas of
California as they are being drained of ground water?
Why is this not of concern to our city government? (I don't get it)
Sincerely,
Georgia
On Apr 25, 2015, at 2:32 PM, Skip Shapiro <sailorskipca@yahoo.com> wrote:
Dear Mayor Holman and City Council,
This is a request for the Planning Department and the City Council to take immediate action to
stop groundwater pumping which occurs during the construction of residential basements.
As long time Palo Alto residents, we are appalled to see millions of gallons of groundwater
going down storm drains in the midst of this historic California drought. At the same time,
residents and businesses have been asked to curtail water use for landscape and other uses. Even
worse, the pumping depletes groundwater that is essential to the health of trees, causes
subsidence that can damage property, and consumes water Palo Alto relies upon for emergencies.
This morning we passed a home under construction on Harker where groundwater is being
pumped. We estimated the flow rate to be 75 gallons per minute (based on the fill time of a 5
gallon bucket), which equates to 108,000 gallons – or 14,400 cubic feet – per day. From past
experience monitoring similar groundwater pumping for basement construction, the pumping will continue for at least 4 weeks. That amounts to more than 400,000 cubic feet of wasted water.
Residential basement construction is a relatively recent phenomenon in Palo Alto, driven by
people maximizing living space within lot coverage constraints. It has likely contributed to the
steep increase in property values and encouraged buyers who raze existing houses to replace
them with new ones that include basements…without considering the impact on neighbors, the community, and the environment.
We think it’s time to halt approval of residential construction that includes basements where
groundwater pumping is required. Basements should not be allowed on these sites. We request
an immediate moratorium on design and construction approval for any home where groundwater
pumping is required. We also ask the City Council to direct the Planning Department to review and change regulations that permit residential basement construction.
Respectfully,
Barbara and Skip Shapiro
Mr. James Keene
General Manager
City of Palo Alto
250 Hamilton Avenue
Palo Alto, CA 94301
Dear Mr. Keene,
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Valoran P. Hanko --r ' . c, rvvk-·on
864 Fielding Court uOJ)\ ce l)'KJ ).j.)\J 1
Palo Alto, CA 94303-3645
May 19, 2015
I recently noticed a pumping operation in my neighborhood at 804 Fielding Drive that is reminiscent of an
operation that occurred next door at 858 Fielding Ct in 2001. This pumping operation takes ground water from our
underground aquifer and sends this to the storm drain as undesirable waste in preparation of a new residential
construction. When this operation was performed in 2001, the surrounding neighborhood sank in elevation
resulting in a new designation for the neighborhood to be within the 100 year flood zone, where as prior it was
not. Additionally, this resulted in cracks in the pavement of our street where the sinking of the ground is still
evident. Additionally, it was observed by some neighbors that their house slab foundations (characteristic of the
1940's period-build homes) had shifted and cracked. The house behind us had their garage drop in elevation in
one of their corners. I estimate that non-potable water is being pumped at a rate of about 0.5 gal/sec, which
equates to 30 gallons per min, 1800 gal per hour, 43,200 gal per day, 302,400 gal per week. Since this operation
went for about 6 months at the next door neighbor's site, assuming a constant rate, this amount of water would
be equivalent to (at 1.2 million gallons of water per month) 7.2 million gallons of underground water. Since the
volume of water occupying 1 gallon is 0.134 cubic feet per gal (7.48 gal per cubic feet), 7.2 million gallons would
take 970,000 cubic feet of underground aquifer space, and it is a fact that when the ground collapses into this
aquifer space, it can never be retrieved again. The loss of elevation in the neighborhood places financial burden
upon innocent people, causing many with mortgage payments to be required to have FEMA Flood Insurance, and
even those who own their house, puts them at new risk of flooding. I believe this pumping action, apparently
approved by the City Building Department, has not been seriously evaluated for its consequences by qualified
engineers without bias. Furthermore, this precious water is being wasted into the storm drain during a severe
drought, another irresponsible action. I am not sure about the legal consequences of halting this operation in my
neighborhood, but as General Manager you must have some power to take emergency actions when severe
consequences can be seen or is discovered, and thus this letter is to inform you of this matter with the hope that
you can stop this pumping process and new building permit approvals, and to suspend all current operations until
appropriate state-of-the-art engineers have evaluated this type of operation. Meanwhile, I intend to contact the
Santa Clara County Water Resources Board about this concern, and hope you may work together with them to
seek a resolution that does not adversely impact the community, one that includes the preservation of our
underground aquifer.
//~.:c•r•I:? / /fj ~~/ / ~···
1. c{c:~ l~ i
Valoran P. Hanko ·
PUBLIC WORKS
CITY OF P.O. Box 10250
PALO
ALTO
Palo Alto. CA 94303 ·
650.329.2151
July 6, 2015
Valoran P. Hanko
864 Felding Court
Palo Alto, CA 94303-3645
Dear Mr. Hanko:
Thank you for your May 19 letter concerning the impacts of basement construction groundwater
pumping. I've been asked to respond on behalf of Palo Alto City Manager Jim Keene. Your letter
expresses concern about a current pumping site and one that took place in 2001, both in your
neighborhood.
With respect to the earlier pumping, you expressed the belief that the pumping caused the ground
to subside. We do not have reason to think that is the case. The additions to the flood zone that
were made around that time were the result of new, better data, as opposed to any anticipated
change in actual elevations. The earlier flood zone map had been based on a more limited set of
elevation measurements. When more elevation data was collected in the 2000 time frame, it
resulted in relatively small shifts in the flood zone boundary, but ones which were very important
to the individual houses affected. You calculated the rough amount of ground water pumped out
and postulated that that the ground level would sink to a level associated with that loss of water.
We do not believe that would be the case. Rather, the groundwater is moving and new ground
water would fill behind the groundwater being pumped out. Only a large number of wells
operating over a long time frame would cause a relatively permanent change in the ground water
elevation and an associated ground level subsidence. As you know, subsidence has occurred in a
number of areas where large numbers of wells have pumped over time.
You also expressed the view that the pumped water going to the storm drain was being wasted.
And yet this ground water was moving toward our creeks and Bay and ultimately would have
replenished both. Pumping some of it to the storm drain results in it traveling a different path, but
ultimately reaching the same locations: our creeks and Bay. Our creeks and Bay need this water to
preserve ecosystems and maintain needed salinity levels.
Nonetheless, because of the strong feelings of a number of our residents, we are working to have
builders minimize the amount pumped and use as much of the water as practical. Builders are now
required to build "Fill Stations" at their sites so that others can fill trucks and tanks and use the
water. The current pumping site at 804 Fielding near you has a Fill Station. The City, other builders
and residents like you can use the water. Please see our website for the other locations and
contact information: www.cityofpaloalto.org/water.
C ityOf Pa lo A lto.org
Printed with soy-based inks on 100% recycled paper processed without chlorine.
I hope this addresses your concerns. Please do not hesitate to contact Mike Nafziger (650-617-
3103) for more information about 804 Fielding, or myself (650-279-0464) for broader issues we
are facing in this most difficult time of drought.
Sincerely,
cfi?:f il,&t
Phil Bobel
Assistant Director, Public Works
From: "Andrei Sarna-Wojcicki" <andreisarna@gmail.com<mailto:andreisarna@gmail.com>>
To: "Council, City" <city.council@cityofpaloalto.org<mailto:city.council@cityofpaloalto.org>>,
"letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com>"
<letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com>> Cc: "Deborah Harden" <deborahrharden@gmail.com<mailto:deborahrharden@gmail.com>>
Subject: Fwd: Groundwater is wasted by pumping at construction sites and dumping into storm
sewers
To: Mayor of the City of Palo Alto and the City Council:
I have sent this message to the Public Comment web site two of days ago, but have not received
an answer, and the matter is urgent. I have also sent it previously to the Palo Alto daily news site
(letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com>). So, I'm forwarding this
email to you and the City Council. By now, three days have elapsed since I sent the first message, and an estimated minimum of 260,000 gallons of groundwater have been pumped from the construction site at 2133 Webster and dumped into the storm sewer at the corner of N.
California and Byron Streets. The water continues to be pumped as I write this (I just went by
there a few minutes ago).
Putting up a sign saying that the public can help themselves to the water does not solve the problem of this wasteful practice, continued with city approval during a time of extreme
drought. As I mentioned in the message, this is just one of several construction sites in the city
where pumping of groundwater is going on. This is a wasteful practice during ordinary times,
and more so during the current severe drought. The water needs to be used for watering the trees and green areas of the city, and to maintain the level of the groundwater to keep city and residential trees from dying.
The excavation at the Webster site must be at the site of a buried old gravel channel, to account
for the high discharge. The water that is being wasted by direct dumping into the storm sewers not only deprives the trees in the vicinity of the pumping and downstream in the water table, but it also depriving a whole ecosystem at lower elevations downstream in the water table to the
southeast--the marshes and the city Baylands.
This is a high price to pay for allowing cellars to be built in an area that is at low elevations (the Webster St. site is at ~17 feet above sea level). Another several such construction sites have been recently finished near our house on Garland Drive. These are at an even lower elevation,
10 to 15 feet. Building cellars in these areas is a mistake, and has been historically avoided in
this area since early European settlement for very good reasons. The water table here is high and
irregular in elevation. Some of the new cellars actually intrude below the water table, as appears to be the case at the Webster Street site.
I urge you to take this matter under advisement. Additional comments and arguments are
provided in the forwarded email.
Sincerely,
Andrei M. Sarna-Wojcici,
Resident of Palo Alto (708 Garland Drive)
Retired geologist, U.S. Geological Survey
---------- Forwarded message ----------
From: Andrei Sarna-Wojcicki <andreisarna@gmail.com<mailto:andreisarna@gmail.com>>
Date: Thu, May 7, 2015 at 10:41 AM
Subject: Groundwater is wasted by pumping at construction sites and dumping into storm sewers
To: letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com> Cc: Deborah Harden <deborahrharden@gmail.com<mailto:deborahrharden@gmail.com>>
Dear Sir or Madam:
Groundwater is being wasted on the Peninsula by being pumped out at construction sites and dumped into city storm sewers. This practice is actively going on at at least three construction
sites in Palo Alto, and probably at many more throughout the Peninsula.
I passed by one such site at 2133 Webster St. in Palo Alto at ~10:45 AM yesterday, returned by
there at ~12:45 noon, and passed by there again at ~5:45 PM. The water was going full blast the whole time from the construction site, around the block to N. California and Byron streets, and
down into a storm sewer. I estimated that about a gallon of water was dumped every second
from a six-inch diameter pipe, which would amount to about 25,200 for the 7 hours time of my
observation. This is probably a minimum for this particular site for this day. At the calculated
rate, this would amount to 86,400 gallons of water for a 24 hour period. My wife observed the same practice going on a few months ago from another site, for at least a week.
This is a massive waste of groundwater during a period of severe drought. It depletes water from
an already depleted water table, forming a cone-shaped depression around the pumping site, and
decreasing the available groundwater in that area from flowing farther down in the water table toward lower elevations, thus lowering the water table and depriving trees from water. It's
killing off our trees.
This water needs to be used for watering the trees and other plants in the municipal parks and
other public grounds, and any left over water should be made available for residential use. Reservoirs need to be constructed to store this water, and a distribution system be put into
place, perhaps even by temporary above-ground plastic pipe systems during this drought, to
make use of this water.
At the dump site that I observed, a sign put up by the city of Palo Alto which informs the public that the water is not potable, that it is being discharged (no duh), and states that "...To use this
water for irrigation pr other non-potable purposes, follow this discharge hose back to the water
filling station." I presume this refers to the pumping site at 2133 Webster. And what does the
Palo Alto citizen do then? Bring a Dixie Cup and help himself/herself to the water? Or back-up
a tanker truck to the site and fill-up? This is obviously a large job that the Peninsula municipalities need to address.
I sent a message regarding this situation to the city of Palo Alto today.
I attach photos from the pumping and dump sites I observed yesterday.
Sincerely,
Andrei Sarna-Wojcicki,
Resident of Palo Alto
Comments to Council regarding Dewatering Residential Basement Construction
Keith Bennett
November 9, 2015
The City of Palo Alto has a history of developing policies to protect natural resources, to protect
our environment and to encourage sustainability. Water is now recognized as a valuable and
limited resource, and groundwater is an important component of the City of Palo Alto’s
Emergency Water Supply. Climate change is predicted to increase the risks of droughts,
megadroughts and floods, in addition to sea (and Bay) level rise.
https://www.washingtonpost.com/national/health-science/todays-drought-in-the-west-is-
nothing-compared-to-what-may-be-coming/2015/02/12/0041646a-b2d9-11e4-854b-
a38d13486ba1_story.html
1) The Groundwater Supply Feasibility Study performed by Carollo Engineers for the City of
Palo Alto in 2003 provides quantitative analysis and measurements of the effects of
groundwater pumping in Palo Alto. Data from the pumping in 1988 of groundwater for
local domestic water use was deemed to be the most reliable and is the primary basis for
the conclusions of the report, which is available at:
http://www.cityofpaloalto.org/cityagenda/publish/uac-meetings/1930.pdf
Some main points are summarized below. In this section, quotes indicate verbatim text
from the study, italics indicate my personal analysis using other information including map
data. Text not in quotes are my personal summaries of information from the study.
a. “Utilizing the data from the 1988 pumping, the extraction of 1,000 acre-feet from
the Palo Alto area will result in basin-wide water level declines on the order of 15
feet.” --- pg. 20
The shallow surface aquifer level, typically a few feet below the ground surface,
declines in response to pumping the deeper aquifer as shown by the well level graphs.
--- pgs. 5 - 10
b. The water levels in the Fernando, Middlefield and Matadero wells were lowered by
18, 25 and 37 feet respectively, even though water was not pumped from any of
those wells. --- Table 1, pg. 13
An interactive map showing the locations of the wells and 2015 basement
dewatering sites is attached (Map A) with this document and available online at:
https://www.google.com/maps/d/edit?app=mp&hl=en_US&mid=zW7thpaYaYZI.kYz
YfTCRxd_Q
The Middlefield well is located about 5 blocks (0.4 miles, straight line) from the
Rinconada Well (from which 600 acre-feet of water was produced in 1988) and about
0.7 miles from the Hale Well (produced 400 acre-feet in 1988).
Peers Park (produced 400 acre-feet) is the closest well to the Fernando and
Matadero wells and is 1.0 – 1.2 miles away.
c. “Depending on the method, estimates of average annual recharge to the basin are
between 38 and 3,800 acre-feet. “ -- Pg. 20
d. “The year-to-year 500 AFA* extraction is intended to not lower groundwater levels
substantially, which would preserve the natural groundwater flow direction and
prevent saltwater intrusion. The periodic 1,500 AFA well use described above
would result in transient occurrence of water levels below sea-level. While water
level below sea-level will reverse the seaward gradient, the slow travel time of
groundwater provides a buffer from seawater intrusion for transient use. “ – Pg. 21
* AFA = Acre-feet annually.
2) The total amount of groundwater pumped for residential basement construction in 2015 is
estimated to be about 400 acre-feet, based upon an average of 1.2 million cubic feet (28
acre-feet) per basement for the 14 basements dewatered in 2015.
3) The Groundwater Supply Feasibility Study estimates that the water table is lowered
approximately proportionately to the amount of water pumped. Using the value in the
report of 15 feet lowering for 1,000 acre-feet pumped, the estimated lowering of the water
table due to dewatering for residential basement construction in 2015 would therefore be
about 6 feet, and would extend over large areas of Palo Alto.
4) An advisory Measure N, “Emergency Underground Water Storage and Equipment
Replacement,” (November 2007) passed with 91.84% of the vote. The Emergency Water
Supply Project (EWSP), WS-08002, was approved by Council in 2007 and bonds totaling
$35,015,000 were sold on October 6, 2009. Of this amount, approximately $5.36 million
was used for projects related to using groundwater: groundwater feasibility studies (CMR
124:06 and related), rehabilitation of existing wells (CMR 232:10) and construction of new
wells (CMR 371:09). The bonds are being repaid over 25 years through water usage fees.
5) As part of the EWSP, five existing wells have been rehabilitated for use as emergency
domestic water supplies. These wells are the Hale Well (999 Palo Alto Avenue), Rinconada
Well (1440 Hopkins Avenue), Peer’s Park Well (1899 Park Boulevard), Matadero Well (635
Matadero Avenue) and Fernando Well (410 Fernando Avenue).
http://www.cityofpaloalto.org/gov/depts/utl/eng/water/wells/faq/rehabilitation.asp
Additionally, two new wells have been constructed, one at Eleanor Pardee Park and another
at (Rinconada) Library / Community Gardens.
http://www.cityofpaloalto.org/gov/depts/utl/eng/water/wells/eleanor.asp
Two 2015 dewatering sites are within the triangle formed by the two new wells (Eleanor
Pardee Park and Library / Community Gardens) and the Rinconada well. See attached Maps
B and C or online map.
https://www.google.com/maps/d/edit?app=mp&hl=en_US&mid=zW7thpaYaYZI.kXmqQlQL
K9iM
6) Methods exist for residential basement construction that do not require dewatering.
Residential basements are built in areas of high groundwater in The Netherlands without
dewatering, per personal verbal communication with the mayor of Palo Alto’s sister city,
Enschede at the Council Meeting on November 2.
Map A: Palo Alto Emergency Water Supply Well Map
Locations of Palo Alto's
Emergency Water Supply
Wells, including the
Middlefield Well.
Basement dewatering sites
Emergency Water Supply Wells
Rinconada Well
Hale Creek Well
Peers Park Well
Matadero Well
Fernando Well
Eleanor Pardee Park Well
Library Community Gardens
Well
Historical Wells
Middlefield Well
Map B: Dewatering_Map 2015
Residential basement construction dewatering sites and emergency water supply well
locations
2015 Basement dewatering sites
2133 Webster St
2130 Byron St
713 Southampton Dr
897 Southampton Dr
736 Garland Dr
684 Wellsbury Way
804 Moreno Ave
1812 Bret Harte St
1210 Newell Rd
51 Jordan Pl
2230 Louis Rd
1405 Harker Ave
3832 Grove Ave
1950 Newell Rd
Emergency Water Supply Wells
Rinconada Well
Hale Creek Well
Peers Park Well
Matadero Well
Fernando Well
Eleanor Pardee Park Well
Library Community Gardens
Well
Map C: Dewatering_Map 2015 (Community center zoom)
Residential basement construction dewatering sites and emergency water supply well
locations
2015 Basement dewatering sites
2133 Webster St
2130 Byron St
713 Southampton Dr
897 Southampton Dr
736 Garland Dr
684 Wellsbury Way
804 Moreno Ave
1812 Bret Harte St
1210 Newell Rd
51 Jordan Pl
2230 Louis Rd
1405 Harker Ave
3832 Grove Ave
1950 Newell Rd
Emergency Water Supply Wells
Rinconada Well
Hale Creek Well
Peers Park Well
Matadero Well
Fernando Well
Eleanor Pardee Park Well
Library Community Gardens
Well
Attachment F
November 2, 2015
To: Palo Alto City Council
From: Keith Bennett
Save Palo Alto's Groundwater
Re: Petitions
Attached are petitions signed by 190 individuals specifically requesting a moratorium on new
dewatering permits for residential basement construction. The signatures were mostly collected during
a short 2 - 3 period in late summer by a handful of volunteers.
Name
Deborah Baldwin
Henry Heller
M Smith
City
Menlo Park
Palo Alto
Palo Alto
Postal Code Signed On
94025 8/6/2015
94303 8/7 /2015
94301 8/7 /2015
City of Palo Alto
GROUNDWATER SUPPLY
FEASIBILITY STUDY
FINAL
April 2003
2700 YGNACIO VALLEY ROAD, SUITE 300 • WALNUT CREEK, CALIFORNIA 94598 • (925) 932-1710 • FAX (925) 930-0208
H:\Final\PaloAlto_WCO\6589A00\Rpt\GWSupplyFeasibilityStdy-Final.doc
CITY OF PALO ALTO
GROUNDWATER SUPPLY FEASIBILITY STUDY
TABLE OF CONTENTS
Page
1.0 INTRODUCTION .......................................................................................................1
1.1 Background .....................................................................................................1
1.2 Well System Rehabilitation and Construction Plans........................................2
2.0 POTENTIAL GROUNDWATER USE IN PALO ALTO...............................................2
3.0 HISTORICAL GROUNDWATER LEVELS AND USE................................................4
4.0 ESTIMATION OF BASIN CAPACITY......................................................................11
4.1 1988 Drought Pumping Analysis ...................................................................12
4.2 Summary of Basin Capacity Estimation ........................................................13
5.0 POSSIBLE PALO ALTO GROUNDWATER SUPPLY SYSTEM.............................14
6.0 POTENTIAL IMPACTS OF GROUNDWATER EXTRACTIONS .............................15
6.1 Subsidence....................................................................................................16
6.2 Saltwater Intrusion.........................................................................................18
6.3 Contaminant Plume Migration .......................................................................19
7.0 SUMMARY...............................................................................................................20
LIST OF TABLES
Table 1 Water Level Response ..................................................................................13
LIST OF FIGURES
Figure 1 Existing and Proposed City Wells...................................................................3
Figure 2 Hale Well.........................................................................................................5
Figure 3 Matadero Well.................................................................................................6
Figure 4 Fernando Well.................................................................................................7
Figure 5 Peers Park Well ..............................................................................................8
Figure 6 Rinconada Well...............................................................................................9
Figure 7 Meadows Well...............................................................................................10
Figure 8 Historical Data on Water Use, Supply, and Subsidence in San Jose, CA....17
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City of Palo Alto
GROUNDWATER SUPPLY FEASIBILITY STUDY
1.0 INTRODUCTION
The Palo Alto Utilities Department (Utilities) is presently examining the issues relating to the
use of groundwater. Examining all water supply options, including local sources such as
groundwater supply, is a part of good planning practices for the water utility. Utilities has
engaged Carollo Engineers, P.C. (Carollo) to prepare a “Groundwater Supply Feasibility
Study” (Study) to:
“Evaluate whether operating one or two of the City’s water wells as active supplies
would cause a significant decrease in groundwater levels or deterioration in
groundwater quality.”
This Study estimates the groundwater basin capacity in Palo Alto vicinity, identifies a
possible well supply system given the basin capacity constraints, and examines whether
there is a safe way to use groundwater as a supply source either in drought periods or on
an ongoing basis. We have examined the capability of Palo Alto’s groundwater supply and
some of the more significant potential impacts of pumping. The three potential impacts that
this Study specifically addresses are:
• The risk of land surface subsidence;
• The risk of groundwater contamination through saltwater intrusion; and
• The risk of groundwater contamination through the travel of pollution plumes to the
drinking water aquifer.
Palo Alto Utilities staff and Carollo have worked closely with staff of the Santa Clara Valley
Water District (SCVWD) to ensure that SCVWD staff are fully informed of the analysis
methods and findings. At the present time, the City of Palo Alto is NOT planning to use
any of the wells for long-term supply. Any change from the planned emergency-only
use of the wells would happen only after further detailed analysis, environmental
review, extensive discussion with the public, and approvals by both the Utilities
Advisory Commission and the City Council. Staff is merely examining the issues
related to the groundwater basin and the possible use of the wells in severe
droughts or as a supplemental supply in the future.
1.1 Background
The City of Palo Alto obtained its well system in 1896. The entire water supply for the City
was derived from groundwater until 1938 when it began receiving supplemental supplies
from the City and County of San Francisco. In 1962, the wells ceased operating on a
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continuous basis and San Francisco water became the City’s primary source of supply with
the wells maintained as an emergency water supply. The wells were last used in 1988 and
1991 to provide supplemental supplies during a serious drought. At this time, the City
maintains five wells as emergency (standby) water sources, but they are in need of
rehabilitation.
1.2 Well System Rehabilitation and Construction Plans
The City is presently implementing plans to rehabilitate the five existing wells and build
three new wells. These improvements are part of a larger Water System Capital
Improvement Plan, which was developed as a result of extensive study completed in 1999
(1999 Study). The primary purpose of the well rehabilitation and construction plans is to
provide necessary emergency water supplies in the event of a complete cutoff from the
SFPUC water supplies.
The overall water CIP has been reviewed and approved by both the Utilities Advisory
Commission and the Palo Alto City Council. Funds for the improvements are included in the
five-year Water Capital Improvement Program Budget.
2.0 POTENTIAL GROUNDWATER USE IN PALO ALTO
The imported water purchased from the SFPUC has been a reliable supply for 40 years.
There is growing concern, however, that this supply may be jeopardized either partially or
completely by a number of factors. For example, the SFPUC supply was rendered
unavailable once in 1995 and again in 1998 due to water quality concerns.1 In addition,
recent studies conducted by the SFPUC have identified a number of system vulnerabilities
that could cut off the water supply for up to 60 days in the event of a serious emergency.2 In
regards to long-term reliability, the SFPUC supply is insufficient to meet the current and
forecasted needs of the users of the regional system it operates. Droughts in 1976-77 and
1987-1992 that resulted in the rationing of supplies clearly illustrates this fact. The SFPUC’s
Water Supply Master Plan (WSMP) recognized that on a long-term basis, its supplies are
inadequate. The WSMP identified the system’s yield as 239 mgd while current demand is
greater than 260 mgd and the demand estimate for 2030 is 303 mgd, or a shortfall in
supplies of 64 mgd. Thus, it is prudent for the City to evaluate its options for improving the
reliability of its water supply.
The location of the City’s wells is shown in Figure 1. These wells may have potential uses
beyond supplying water during SFPUC outages. If the City Council decided, the wells could
also help supplement water supplies during drought periods and perhaps even as active
1 “Water Wells, Regional Storage, and Distribution System Study,” page 4-1, prepared for the City of
Palo Alto by Carollo Engineers, P.C. dated December 1999. 2 SFPUC fact sheet dated August 5, 2002.
FINAL - April 28, 2003 2
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LEGEND
Pa303f1-6589.cdr
Figure 1
EXISTING AND PROPOSED CITY WELLS
GROUNDWATER SUPPLY FEASIBILITY STUDY
CITY OF PALO ALTO
SFPUC Turnout
Existing Well Sites
Proposed Well Sites
No Scale
Matadero
Well
P ers Pa k e r
Wlel
Rinconada
Well
Library/
Community
Gardens Well
El Camino
Park Well
Palo Alto
Medical Facility
Well (Roth Site)
Middlefield
Well
Eleanor
Park Well
Ha e l
Well
Fernando
Well
tt
tt
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California
Turnout
Lytton
Turnout
sources to be regularly used in conjunction with the SFPUC supply. These uses, however,
raise significant concerns related to lowering of the groundwater levels. Significantly,
depressed groundwater levels can potentially lead to environmental consequences such as
subsidence, saltwater intrusion, and contaminant migration. Though there may be other as
yet unidentified impacts, these impacts are discussed in this Study as they are considered
to be the most significant potential impacts.
Currently, the wells are designated standby sources meaning that they can only be used
15 days a year and no more than 5 days consecutively.3 The “standby” designation is made
with the California Department of Health Services (DHS) in part because the well water
quality exceeds some secondary (aesthetic) drinking water standards. According to the
1999 study, the well water quality exceeds secondary standards for TDS, iron, and
manganese.
For the purposes of this Study, it is assumed that the water would be used for potable uses.
As such, changing the well status with the DHS from “standby” to “active” would require the
well water to be treated such that it met all drinking water regulations. Alternatively, the
regulations allow the City to distribute water that meets primary drinking water quality
standards but exceeds some secondary drinking water quality standards. Proceeding in this
manner would require the City to first complete a study acceptable to the California
Department of Health Services (DHS) showing consumer acceptance of water not meeting
secondary drinking water standards (see California Code of Regulations Title 22, Division 4,
Chapter 15, Article 16, Section 64449 for specific details).
Customer acceptability, however, may require the City to install sufficient treatment at the
wells to be used for drought or active supply such that the water quality is increased
significantly or made comparable to the SFPUC water. This issue was covered in the City’s
“Long-Term Water Supply Study” dated May 2000 (May 2000 Study).
3.0 HISTORICAL GROUNDWATER LEVELS AND USE
The best way to evaluate the effect that pumping has on groundwater levels is to review
historical data that show the basin’s response to pumping. Groundwater pumping and water
level data from 1950 through 2000 are presented in Figures 2 through 7. All of the water
level graphs show a characteristic rise following the switch to SFPUC water in the early
1960s.
In general, the graphs show smooth trends in response to recharge, pumping, and drought
conditions. There are occasional spikes in the graphs that appear to be outlying, erroneous
3 According to the California Code of Regulations, Title 22, Section 64449, (e) (I), standby wells may
be used as active sources without additional water treatment if the City were to conduct a study
establishing the customers’ willingness to accept water that doesn’t meet secondary water quality
standards.
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Pa303f2-6589.cdr
Figure 2
HALE WELL
GROUNDWATER SUPPLY FEASIBILITY STUDY
CITY OF PALO ALTO
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CITY OF PALO ALTO
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CITY OF PALO ALTO
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CITY OF PALO ALTO
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data. We believe that the occasional spikes in the data are more likely due to equipment
error than due to the actual water level. The information presented in the graphs is used in
the following section to estimate the groundwater basin capacity in the Palo Alto area.
4.0 ESTIMATION OF BASIN CAPACITY
Groundwater resources of the Palo Alto area occur within a much larger aquifer system -
the Santa Clara Valley Groundwater Basin. This basin extends as far south as Coyote
Narrows and extends north of Palo Alto far into San Mateo County. The system is bounded
by uplifted bedrock to the west. To the east, the shallow portion of the aquifer system is
bounded by San Francisco Bay. At depth, the aquifer systems of the west side of the valley
interfinger under the bay with those of the east.
In a large groundwater basin, estimation of the capacity of a smaller area within a basin is
difficult because the smaller area is, by definition, unbounded. Groundwater moves freely
between basin areas in response to hydraulic head. Therefore, pumping or recharge in one
area of the basin has effects on the basin as a whole. Indeed, the impacts of seasonal
variations in recharge and in extractions by one or more of Palo Alto’s neighbors are
evident in the seasonal rise and fall of the water levels at the Hale Well.
Estimating the capacity of the Santa Clara Valley Groundwater Basin in the Palo Alto area
requires the definition of an arbitrary area for purposes of evaluating changes in
groundwater storage that have occurred. For the purpose of estimating the storage capacity
of the groundwater basin in the Palo Alto area, an arbitrary area was defined. This area is
bounded on the west by the Hanover Fault zone that is approximately 2,000 feet west of
El Camino Real with a similar trend. The Bay was adopted as the eastern boundary. The
Hanover Fault zone separates the alluvium of the basin from the bedrock to the west and is
a hydrogeologic boundary. For the upper portion of the aquifer system that is in hydraulic
communication with the Bay, the Bay is a hydrogeologic boundary. For the deeper portions
of the aquifer system, the Bay is not a hydrogeologic boundary but for purposes of definition
in this Study, it was adopted as a boundary. The adopted north and south bounds are San
Francisquito Creek and San Antonio Road, respectively. The area described by these
boundaries is approximately 9,500 acres.
Given this defined area, there are several approaches to understanding the capacity or
yield. Three methods were evaluated in a previous report to the City entitled “Estimation of
Groundwater Basin Capacity” dated December 2002 (December 2002 Report). Those three
methods are: 1) Use of the SCVWD calibrated groundwater model; 2) Analysis of basin
recovery to cessation of pumpage; and 3) Analysis of basin response to 1988 drought
pumping.
Once the December 2002 report was completed, the City and Carollo met with
representatives of the SCVWD to discuss their questions and concerns regarding the
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report. One of the outcomes of that meeting was that the first two methods of calculating
the groundwater basin capacity were controversial for the following reasons:
• The SCVWD groundwater model does not accurately reflect the hydrogeologic
conditions at Palo Alto. One of the most important deviations is that the model does
not account for any recharge from San Francisquito Creek. In fact, the model has a
boundary condition that sets the contribution at zero. As such, using the model to
calculate the Palo Alto groundwater basin capacity would likely result in a volume that
is erroneously low unless the contribution from San Francisquito Creek is accounted
for. Since this data is not available and obtaining it would not only require an
extensive hydrogeologic study but would also raise concerns regarding the amount of
water that must be left in the creek versus that which can be considered useful for
groundwater recharge and later extraction, this method will not be further developed.
• Using the groundwater level recovery history to calculate the basin storage capacity
yielded values that ranged over two orders of magnitude. SCVWD representatives
recommended that the City should perform multiple aquifer tests to improve the
accuracy of this data. However, the existing condition of the City’s wells is not readily
conducive to performing this type of test. In addition, an aquifer test could readily be
performed once the City has completed upgrading its wells. For the present time, this
method of estimating the basin capacity will not be pursued.
The third method presented in the December 2002 Report for estimating the groundwater
basin capacity (i.e. analyzing the water level data gathered during and after pumping in
1988) will be used for the remainder of this Study.
4.1 1988 Drought Pumping Analysis
The pumping performed by the City of Palo Alto during the drought provides data to directly
estimate the response of the basin to extractions. When the 1987-1992 drought occurred,
the City’s wells had been essentially idle since 1962. During this period, water levels in the
basin had risen, on average, more than 150 feet. Approximately 90 percent of that recovery
took place in the first 10 years following cessation of pumping. The City operated the wells
for an approximately 5-month period in 1988 and extracted approximately 1,505 acre-feet.
The water level response is shown on Figures 1 through 6. The extraction volume and the
observed water level response are summarized in Table 1.
Averaging the observed water level declines results in an average decline of approximately
24 feet. This water level decline reflects Palo Alto’s pumpage while also reflecting the
simultaneous pumpage from neighboring utilities. Utilizing the observed 24 feet of decline
across the assumed 9,500-acre area results in an observed coefficient of storage of
approximately 0.007 (dimensionless). This value is quite appropriate for a semi-confined
aquifer system, such as the Palo Alto area.
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Table 1 Water Level Response
Groundwater Supply Feasibility Study
City of Palo Alto
Well
1988 Extractions
(acre-feet)
Observed Water Level Decline During the
1988 Pumping Period (feet)
Matadero 0 18
Hale 398 15
Fernando 0 25
Rinconda 627 25
Middlefield(1) 0 37
Meadows(2) 123 Data Not Available
Peers Park(3) 357 Data Not Available
Total 1,505 Average = 24
Notes:
(1) Middlefield well water level decline likely reflects proximity (about 0.5 mile) to the
operating Rinconda well. Similar effects are revealed for the Matadero and Fernando
wells indicating that they are in the same basin as the operating wells.
(2) The Meadows well was not highly productive and was destroyed following its use in
1988. No water level data was collected after 1988.
(3) Water level data for the Peers Park well were not collected between the years 1988
and 1994. Subsequent data shows water level variation similar to the Hale well.
Though some groundwater was pumped in 1991, the City ceased significant extractions in
December 1988. Of interest is the rapid recovery of the basin after drought conditions, with
water levels recovering to pre-pumping levels within 18 months of the extraction period.
This also is reflective of the semi-confined nature of the basin and the active recharge
efforts of SCVWD.
4.2 Summary of Basin Capacity Estimation
From the drought pumping analysis presented above, the following conclusions are drawn
regarding the groundwater basin capacity:
• Water levels in the Palo Alto area have returned to almost predevelopment levels.
Essentially, the groundwater basin in the Palo Alto area is full.
• Data from 1988 pumping provides a good example from which to appraise
groundwater extraction concepts. 1,500 acre-feet were extracted with limited impact.
Water level impacts were short-lived and water levels returned to pre-pumping levels
within 18 months. If pumping were performed during a non-drought period, the
drawdown would likely be less. Initial drawdown may also be affected by the condition
of the existing casings that may cause otherwise productive portions of the aquifer to
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contribute to the supply. An aquifer test should be conducted following the City’s well
construction and rehabilitation efforts to verify the basin’s response to pumping.
• Utilizing the data from the 1988 pumping, the extraction of 1,000 acre-feet from the
Palo Alto area will result in basin-wide water level declines on the order of 15 feet.
Historical experience suggests that the basin will recover to pre-pumping levels within
a couple years. It is expected that the water level would decline approximately 25 feet
if the City were to extract 1,500 acre-feet in one year.
• Occasional depletion of storage resulting from extractions in excess of annual
average recharge appears to have minimal adverse impacts.
• Seasonal fluctuations in water level record from Hale and Rinconada wells shows that
Palo Alto’s pumpage does not occur autonomously. Palo Alto’s water level appears to
be impacted by pumpers outside of SCVWD jurisdiction.
From the above analysis, it appears that the following groundwater pumping scenario may
be safely supported by the groundwater basin:
• During drought conditions, 1,500 acre-feet may be withdrawn in one year as long as
the aquifer is allowed to recover to pre-pumping levels before pumping is reinitiated.
• 500 acre-feet per year may be withdrawn on a year-to-year basis. This practice,
however, should be discontinued if the groundwater levels continued to drop to levels
that may induce negative environmental impacts (see discussion below on
subsidence, saltwater intrusion, and contaminant plume migration).
The balance of this study is presented assuming the wells are used to supply 1,500 acre-
feet per year (AFA) during droughts, or 500 AFA on a year-to-year or active basis.
5.0 POSSIBLE PALO ALTO GROUNDWATER SUPPLY SYSTEM
A well system that could provide this level of service would need a capacity of about
1,000 gallons per minute (gpm) assuming the well is operated continuously for the year
during the drought operation (1,500 AFA) or 2,000 gpm if the well is operated for only half
the year. In addition, the well site must be able to accommodate the treatment equipment
that may be required for this operation (as discussed above), and the environmental and
public involvement efforts must conclude that installing treatment is feasible at the site. The
May 2000 Study evaluated the existing and proposed well sites in terms of their relative
ability to be used as drought or active supplies. That study provided the following ranking of
the existing wells:
• Hale and Peers Park are the best sites since they are existing wells that are
high-capacity and have adequate adjacent space for treatment equipment.
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• Rinconada is another existing high-capacity well but it lacks the space needed for
treatment equipment (unless the equipment is constructed at the location of the
existing tennis courts).
• Fernando and Matadero do not have adequate capacity or space to be considered
feasible active or drought supply sources.
At the time the May 2000 Study was written, the City had not yet begun to implement the
proposed new well projects. As such, these wells were generally ranked lower than the
existing wells. The proposed well sites were ranked as follows:
• The El Camino Park site was ranked among the highest because of the size of the
site and its proximity to the SFPUC turnouts and the proposed reservoir, which would
facilitate blending the well water with SFPUC water before it is delivered to the
distribution system.
• The Eleanor Pardee Park, the Library/Community Gardens, and the Roth sites
(Old Palo Alto Medical Facility) were ranked high because of the size of each of these
sites.
• The Middlefield Road well site was ranked lowest because it is the most constrained
site.
It should be emphasized that none of the previous studies included performing either the
environmental, public involvement, or other studies that are needed before any of the above
sites can be considered truly feasible for well or water treatment facility construction. The
City’s current on-going efforts (the Phase I and Phase II Water Supply Capital Improvement
Projects) include performing these needed studies.
If treatment or blending are not required, any of the City’s wells could be used for drought or
active use assuming the required approvals (discussed above) are obtained. If, however,
water treatment facilities must be constructed, it would be best to focus on a single site
since only one well is needed to be within the identified capacity limits. In addition, focusing
the permitting and engineering requirements on a single site is the most cost-effective
approach for the City. For a drought supply with treatment, the best existing well sites are
Hale and Peers Park. The best proposed well site for a drought supply source with
treatment is El Camino, though the Roth site, the Library/Community Gardens, and Eleanor
Pardee Park all appear to be feasible sites at this time.
6.0 POTENTIAL IMPACTS OF GROUNDWATER EXTRACTIONS
The potential impacts from groundwater extractions derive from changes in groundwater
flow directions that result from changes in water levels caused by extractions (pumping). As
a preface to the following sections, a brief summary of the history of groundwater levels in
the Palo Alto area and the Santa Clara Valley is presented.
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Groundwater development in the Santa Clara Valley began around 1900. At that time most
groundwater wells in the lower elevations of the Santa Clara Valley were artesian – that is,
flowing at ground surface. As aggregate extractions increased, water levels fell
progressively, subject to climatic variations, reaching depths of as much as 200 feet below
ground surface by the early 1960s. With the importation of water to the Santa Clara Valley
water levels began to recover. In Palo Alto, water levels are currently at elevations
comparable to the 1910s. In wet winters, wells in the Palo Alto area now, if not controlled,
flow at ground surface.
6.1 Subsidence
One of the potential impacts of groundwater extractions is a decrease in the elevation of the
ground surface known as land subsidence. Some of the negative effects of the subsidence
are an increased risk of flooding, and damage to infrastructure. Subsidence has been
associated to areas with significant groundwater pumping, natural gas production, or oil
production. Groundwater is pumped from porous layers with higher hydraulic capacities,
i.e., sand and gravel aquifers. As the pumping occurs, water from the confining layers of the
aquifers is drawn into the porous aquifer. The aquifers consisting of sand and gravel tend to
be incompressible, however, the confining layers may be compressible materials, such as
clay. When the groundwater is pumped from these compressible layers the soils compress
and the surface elevation starts to drop. This decline in elevation is the result of the physical
properties of clay. Clay is comprised of platy minerals that are commonly oriented randomly
within the clay deposit. With the removal of fluid and overburden pressure, the clay particles
rotate such that they orient parallel with the ground surface. This rotation results in a
decrease in vertical thickness of the deposit. The thickness loss is irreversible and the
resulting elevation loss is permanent. However, land subsidence can be arrested with
increased groundwater levels.
In Santa Clara Valley, extractions since the turn of the century resulted in lowering of
groundwater levels as much as 200 feet (-160 below sea-level). This lowering of water level
resulted in as much as up to 12 feet of subsidence in some locations of the Santa Clara
Valley. Subsidence in the Palo Alto area was between 2 and 4 feet. The amount of
subsidence in a given area was a function of the amount of water level decline and the local
geologic conditions. Areas with shallow bedrock experienced less subsidence than those
areas underlain by sediments of substantial thickness.
The relationship between water levels, pumpage, imported water supply, and subsidence
(as measured in San Jose, CA) is shown on Figure 8. As can be seen in this figure,
subsidence generally correlates with periods of falling water levels. Currently, land
subsidence has essentially stopped in the Santa Clara Valley as a result of the increased
groundwater levels resulting from the use of alternative water supplies and basin
management.
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Pa303f8-6589.cdr
Figure 8
HISTORICAL DATA ON WATER USE,
SUPPLY, AND SUBSIDENCE IN SAN JOSE, CA
GROUNDWATER SUPPLY FEASIBILITY STUDY
CITY OF PALO ALTO
As discussed above, the loss of elevation associated with subsidence is the result of the
reorientation of clay minerals within clay deposits. The compaction of these deposits is
essentially irreversible in that when water levels subsequently rise, the clay minerals do not
return to their original orientation. However, since these materials are now compacted, the
lowering of water levels does not result in significant further compaction. If the City’s wells
were used at the capacity limits considered herein, the result would be a transient lowering
of water levels to levels less than 25 percent of the historical lows. As such, use of the wells
should not result in renewed subsidence.
There was no data collection focused on subsidence in the Palo Alto area during the last
use of the wells (in 1988 and in 1991). The closest subsidence measurement station
maintained by the SCVWD is approximately 10 miles to the south of Palo Alto. However,
there are no known anecdotal reports of property damage from renewed subsidence in the
Palo Alto area during this period of well use.
6.2 Saltwater Intrusion
The movement of saltwater into freshwater aquifers is called saltwater intrusion. Under
natural conditions, groundwater flows from areas of recharge on the land to areas of
discharge; in coastal areas these are commonly the ocean or the bay. If groundwater
extractions result in on-land water level elevations below sea-level, groundwater flow
directions reverse and seawater moves from the ocean into coastal aquifers. Although the
most common mechanism of seawater intrusion is the lateral movement of seawater
through the offshore exposure of the aquifer, seawater intrusion can also occur vertically
where depressed water levels in underlying aquifers induce flow from overlying water
bodies into the aquifer. If the overlying water body is saline this also results in a type of
seawater intrusion. This vertical movement of seawater is often distinguished from lateral
movement of seawater by the designation of seawater infiltration.
The coastal portion of the Santa Clara Valley aquifer system has historically been impacted
by both seawater intrusion and seawater infiltration. Groundwater extractions in the Santa
Clara Valley from the turn of the last century until the 1970s resulted in the maintenance of
groundwater elevations that were chronically and increasingly below sea-level. As
previously mentioned water surface elevations in the Palo Alto dropped at as much as
140 feet below sea-level. This resulted in the on-land movement of seawater from the Bay
and in many areas the vertical movement of seawater from Bayland ponds used for salt
harvesting and aquaculture. The rate of intrusion/infiltration is governed by the magnitude of
the gradient: the steeper the gradient, the more rapid the movement of water through the
aquifer. Seawater intrusion and infiltration has been arrested as the result of reduced
groundwater extractions, water importation and basin management efforts.
While currently arrested, seawater intrusion could be reactivated if water levels were again
chronically below sea-level. However, because groundwater moves very slowly, the short-
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term occurrence of below sea-level water levels, while briefly reversing the flow direction,
results in little actual transport of saline groundwater. What transfer does occur, is reversed
when flow directions return to normal. This would be the case for either the emergency
supply operation for which the wells are currently permitted, or the possible drought supply
that is discussed herein.
6.3 Contaminant Plume Migration
Groundwater extraction modifies its natural flow direction. In the vicinity of an extraction
well, groundwater flow directions are altered both vertically and horizontally resulting in the
production of water from the well. Water produced from the well derives from a recharge
area surrounding the well, the size and shape of this recharge area being a function of the
hydrogeology and well design. This recharge area is commonly referred to as a capture
zone of the well.
If there are sources of contamination within the capture zone of a well, the well can become
contaminated. Within an urbanized setting, the potential sources of groundwater
contamination are limited to contamination associated with industrial and commercial land
uses. Predominantly this is in the form of leaky underground storage tanks. This would
include gas stations, industrial solvents from manufacturing or research, and dry cleaners.
As part of the 1999 Study, all sources of contamination known by regulatory agencies were
reviewed to determine the risk to City’s existing wells and proposed new well sites. This
review revealed very few contamination sites in the areas surrounding the existing and
proposed well sites. Most of the existing contamination is in the more industrial portions of
the City – those portions west and south of the downtown area. Fortuitously, these areas
are not the areas of the City with the most favorable hydrogeologic characteristics for water
supply wells.
The only identified contaminated sources in the area near the existing or proposed wells
were the Shell gas station on Alma Street and the City of Palo Alto Fire Station. These
locations are proximate to the proposed El Camino Well, and they both had leaky
underground gasoline storage tanks. Both sites have been cleaned up and closed by the
Regional Water Quality Control Board.
The use of the wells at the capacity limits considered herein will temporarily modify
groundwater flow patterns in the vicinity of the wells creating the potential for capture of
contaminate plumes. However, based on available records there are no known contaminate
plumes within the capture zones of the City’s existing or proposed wells.
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7.0 SUMMARY
Once refurbished, the City’s five existing wells and the three proposed new wells will
provide an excellent standby water source to be used during water supply emergencies
such as a shutdown of the SFPUC system. If the Palo Alto City Council decided to use the
wells during droughts or as supplemental sources to be used in conjunction with the
SFPUC supply, the wells could also provide added benefits in terms of enhancing the
reliability and redundancy of the City’s water supply. Any regular use considered in the
future, however, should not exceed the reliable capacity of the groundwater basin to avoid
such negative environmental consequences such as subsidence, saltwater intrusion, and
contaminant migration.
Groundwater pumping and water level data for the last 50 years were analyzed to help
evaluate the basin’s response to pumping. It should be noted that the data collection and
analysis is too limited to draw firm conclusions regarding the reliable basin capacity or
sustainable yield that the City may be able to pump on an active basis. In addition, these
values could only be derived after analyzing and accounting for natural recharge patterns
and the pumping plans of the City’s neighboring utilities. To provide an initial analysis on
issues related to other-than-emergency use of the wells, however, the following may be
inferred from the data analysis presented herein:
• Water levels in the Palo Alto area have returned to almost predevelopment levels.
Essentially, the groundwater basin in the Palo Alto area is full.
• Depending on the method, estimates of average annual recharge to the basin are
between 38 and 3,800 acre-feet. A conservative year-to-year value is likely on the
order of 500 AFA.
• Data from 1988 pumping provides an example from which to appraise groundwater
extraction concepts. 1,500 acre-feet were extracted with limited impact. Water level
impacts were short-lived and water levels returned to pre-pumping levels within
18 months. If pumping were performed during a non-drought period, the drawdown
would likely be less. These values should be revisited through an aquifer test
performed following the City’s well construction and rehabilitation efforts.
• Utilizing the data from the 1988 pumping, the extraction of 1,000 acre-feet from the
Palo Alto area will result in basin-wide water level declines on the order of 15 feet.
Historical experience suggests that depending on climatic conditions, the basin will
recover to pre-pumping levels within a year or so. It is expected that the water level
would decline approximately 25 feet if the City were to extract 1,500 acre-feet in one
year. This decline, however, is not likely to induce significant detrimental
environmental impacts since it is much less than the historical drawdown levels and is
transient in duration.
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• Occasional depletion of storage resulting from extractions in excess of annual
average recharge appears to have minimal adverse impacts.
• Seasonal fluctuations in water level record from Hale and Rinconada wells show that
Palo Alto’s pumpage does not occur autonomously. Palo Alto’s water level appears to
be impacted by pumpers outside of SCVWD jurisdiction, possibly Menlo Park and
East Palo Alto. Under drought conditions, impacts of all local pumpers will be
superimposed on water level conditions.
The limited analysis suggests that sustained year-to-year extractions of approximately
500 AFA may be possible with negligible water level decline. The actual extraction value
would be dependent on the location and depth of the well, how many wells were being
operated, and the extent at which neighboring utilities were operating their wells and
climatic conditions. If extractions were periodic, as in response to drought or delivery
reductions, extractions of 1,500 AFA are possible provided this use is short-lived (one year
every three or so years) and the basin is allowed to recover after this use.
These estimates were based on the best available data and on general knowledge of
groundwater basin behavior. However, the data was limited, as the basin has not been
actively pumped since 1963. When more information becomes available both from
developing the City’s wells for emergency use and from data collected from the SCVWD’s
monitoring well, these estimates will be re-examined.
The level of well use described above is not expected to result in reinitiation of subsidence
or seawater intrusion or the movement of contaminate plumes for the following reasons:
• Reinitiation of significant subsidence would require the dewatering of sediments not
dewatered as part of the water level declines of the last century. This would require
water level declines of more than 140 feet. As proposed the operation of the wells
would result in short term water level declines of between 20 and 30 feet, and
dewatering of previously dewatered and compacted sediments.
• The year-to-year 500 AFA extraction is intended to not lower groundwater levels
substantially, which would preserve the natural groundwater flow direction and
prevent saltwater intrusion. The periodic 1,500 AFA well use described above would
result in transient occurrence of water levels below sea-level. While water level below
sea-level will reverse the seaward gradient, the slow travel time of groundwater
provides a buffer from seawater intrusion for transient use.
• Operation of the wells would result in temporary disruption of natural flow directions
and could effect movement of contaminate plumes. However, no known contaminate
plumes exist proximate to the existing or proposed wells sites.
City of Palo Alto (ID # 6450)
Policy and Services Committee Staff Report
Report Type: Agenda Items Meeting Date: 12/15/2015
City of Palo Alto Page 1
Summary Title: Basement Construction Dewatering Update
Title: Update on 2016 Next Steps on Basement Construction Dewatering
Program and Discussion and Potential Recommendation to Council Regarding
Ideas From Committee Members for Additional Project Work
From: City Manager
Lead Department: Public Works
Recommendation
Staff recommends that the Policy and Services Committee review and discuss this Staff Report
and provide direction. Staff recommends that Group 1 (most time-sensitive) items not return to
Policy & Services but that staff develop those recommendations into actionable items for City
Council approval, as needed. Our goal would be to return to Council as soon as possible in
2016. Group 2 and 3 items will be brought back to Policy and Services as indicated below.
Executive Summary
The Policy and Services Committee discussed staff recommendations on investigating program
enhancements for basement construction dewatering at its December 1, 2015 meeting
(Attachment A: #6268) and heard public testimony (Attachment B: correspondence). The Chair
requested that staff summarize the wide range ideas suggested by individual Committee
members for follow-up to ensure that all were captured to facilitate potential further discussion
by the Committee. (see ID# 6438). The ideas are organized into three groups.
Group 1 is a set of potential new requirements for the 2016 construction season that staff
recommended on December 1 and would continue to investigate with a goal of swift
implementation; Group 2 is for ongoing and potential future work for gathering information
about the groundwater basin; and Group 3 is a list of additional (some big) ideas generated at
the meeting. With respect to Group 3, staff will return to the Committee in the first half of 2016
with questions that should be considered as part of a further discussion with the Committee
about whether to recommend Council consideration and potential direction on any of these.
The potential scope of the items could make this a major new initiative and will require careful
assessment of the resources necessary to support them, in the context of other work priorities.
Assuming the committee accepts the staff recommendations, we will continue to share our
City of Palo Alto Page 2
thinking with various stakeholders, as part of our deeper dive into implementation details of
Group 1. This is important as new house construction applications are being submitted and it is
important that we advise people of our potential planned changes, even before they could go
into effect. We expect that some aspects of the recommendations in Group 1 could require
specific Council action, so staff attention needs to be directed to work through the details of
new requirements so that we can get to Council in early 2016.
Discussion
Below is a summary of the potential program changes identified by Staff and Committee
members at the December 1, 2015 Policy and Services Committee meeting:
Group 1: New Basement Dewatering Submittal, Fill Station and Groundwater Use
Requirements
Staff will continue to work (investigate feasibility and practicality) on the five program
enhancements brought forward for consideration at the December 1, 2015 Committee
meeting. Staff has added a bit more information to some of the Group 1 recommendations
below.
1. Encourage greater fill station use through public outreach and enhanced signage.
2. Strengthen outreach on the water cycle and value of fresh water flows to storm drains,
creeks and bay.
3. Refine requirements for Groundwater Use Plans; including maximizing on-site water reuse,
at least one day per week water truck hauling service for neighbor and City landscaping, and
piping to nearby parks or major users where feasible.
4. Expand fill station specifications to address water pressure issues from multiple concurrent
users, including separate pumps for neighbors where needed and sidewalk bridges for hoses.
5. *Broaden the City’s Basement Pumping Guidelines to specifically require a determination of
effects on adjacent buildings, infrastructure, trees, or landscaping. Applicants would determine
the location of the temporary groundwater cone of depression caused by pumping. Avoidance
measures would be required to be included in the determination if offsite effects are
anticipated. City Urban Forestry staff may develop guidelines for avoidance measures such as
soil enhancements and supplemental watering of neighboring landscaping by project
applicants. Additional measures to avoid effects could include adjusting the location, depth or
duration of pumping or altering construction methods to minimize or eliminate pumping.
Additional considerations raised at the Committee meeting include:
Ensuring that fill stations are compliant to specifications
Two committee members did not find outreach on the water cycle (2) to be a priority
City of Palo Alto Page 3
Staff recommends continuing to investigate these Group 1 program enhancements and then
finalize new requirements on basement dewatering for approval, as needed, by the full Council
in early 2016.
Group 2: Gathering of Groundwater Information and Plans by Palo Alto and its Partner
Agencies
Continue working with the Santa Clara Valley Water District (Water District) in an already
ongoing effort on developing a further understanding of the North County groundwater
systems, impacts of groundwater pumping, and opportunities for enhanced groundwater
recharge. A Water District key mission is to manage the County’s groundwater; therefore, staff
will collaborate closely with the Water District, and the new Council-level Recycled Water
Committee. This collaboration may also include working with San Mateo County and its cities
to ensure coordination with their development of a groundwater strategic plan.
Staff will provide an update on the work plan for this effort to the Policy and Services
Committee/(City Council?) in the first quarter of 2016.
Group 3: Further Ideas Brought Forward by Individual Policy & Services Committee Members
Individual Committee members articulated additional ideas and suggestions. Some of these
ideas are multifaceted and complex, and will require sustained effort from staff and assistance
from consultants over multiple years. The Committee and Council will need to evaluate
priorities and timelines, including the potential that significant new assignments may delay
other projects currently underway. Staff will prepare a report for the Policy and Services
Committee in the first half of 2016 to discuss these matters and the development of a potential
recommendation to Council to direct additional work in one or more of these areas:
1. Charging for discharge of groundwater. The current fee for dewatering to the storm drain
system is $80 per month. This effort would consider increased fees to charge for the use of the
City’s storm drain system and staff time to manage the dewatering requirements. Committee
members suggested exploring whether the fee that the Santa Clara Valley Water District
charges for groundwater pumping would be an appropriate baseline.
2. Developing dewatering requirements tailored to drought situation.
3. Developing approaches to ensure that multiple basement pumping is not happening in close
proximity (distance and time), and instead is spaced out, essentially allowing only a limited
number of basement construction dewatering in one area.
4. Addressing potential damage from dewatering through bonds or insurance.
City of Palo Alto Page 4
5. Further study of all pumping activities in the City, including private wells, City Hall garage,
Oregon Underpass and other underpasses.
6. Review of basement building and zoning code issues, including FAR adjustments for
basements and not allowing two-story basements, or any basement, in areas with shallow
groundwater. (Note: Staff’s initial reaction is that utilizing zoning to implement these
requirements may be quite difficult because groundwater depth can vary significantly from
block to block)
7. Review of impacts of multiple basements on soil absorption and/or the creation of barriers
to groundwater flow.
8. Investigation of costs of other construction methods that do not require dewatering, or as
much dewatering.
9. Investigate whether Palo Alto should assume a groundwater management leadership role
for the North County area. (Including consideration of staff time and cost implications.)
10. In addition, Committee members were interested in how increased use of permeable
surfaces may assist with groundwater recharge. (Note: City staff can provide an update on the
new stormwater permit requirements for a Green Infrastructure Plan which will require more
infiltration of stormwater into the ground rather than discharging it through storm drains via
both public and private projects.)
In summary, staff will finalize its investigation of Group 1 activities for implementation of
potential new requirements starting in 2016. Group 2 is part of an ongoing effort and the
Committee and Council will be updated periodically. The Group 3 activities will be brought to
the Committee /Council for discussion and direction to study them; Staff is making no estimate
on when they could be implemented.
Resource Impact
Testing and refining the suggested measures to improve the dewatering program or any other
measures suggested by the Committee will require significant staff time that is currently
allocated to other projects. For the homeowner, these measures may increase basement
construction project costs.
As mentioned in earlier parts to this report, the Group 1 recommendations have sent staff
scurrying to develop final recommendations for action. The Group 3 suggestions are varied and
require thoughtful review and potentially large costs. In every case, consideration of our ability
to fund and support or absorb the efforts will be required.
City of Palo Alto Page 5
Environmental Review
The suggested program enhancements are minor modifications to an existing regulatory
program designed to be protective of the environment. They would be covered by the general
rule that California Environmental Quality Act (CEQA) does not apply where there is no
possibility an action could have a significant effect on the environment (State CEQA Guidelines
Section 15601(b)(3)).
Attachments:
-: Attachment A: 120115 6268 Basement Construction Dewatering (PDF)
-: Attachment B: Correspondence (PDF)
City of Palo Alto (ID # 6268)
Policy and Services Committee Staff Report
Report Type: Agenda Items Meeting Date: 12/1/2015
City of Palo Alto Page 1
Summary Title: Basement Construction Dewatering
Title: Consider Tentative Staff Recommendations On Further Requirements
for Basement Construction Dewatering Program for 2016
From: City Manager
Lead Department: Public Works
Recommendation
Staff recommends that the Policy & Services Committee direct staff to continue
considering five program enhancements, presented in the “Discussion” section
below, on basement construction dewatering; and implement those found to be
feasible and practical by Spring 2016 to address public concerns raised during the
summer of 2015.
Executive Summary
Over the years, basement construction groundwater pumping has generated
public concern in Palo Alto; the ongoing drought and mandated water restrictions
this past summer escalating those concerns. Public concerns relate to the
apparent wasting of water by discharging to storm drains, potential impacts on
groundwater elevation and flow volume, as well as potential impacts on
neighboring properties, such as subsidence and cracks, and impacts on trees and
other landscaping.
In response to these concerns, staff has developed potential enhancements to the
City’s existing regulations regarding construction dewatering for review and
discussion.
Background
Basement construction is often required for non-residential, mixed use and
multifamily residential buildings, particularly if underground parking is included in
City of Palo Alto Page 2
the proposal.1 Additionally, the high value of land and housing in Palo Alto
translates into residential property owners seeking to increase their single family
homes by constructing basements. Basements constructed in R-1 districts do not
count towards allowable square footage (regulated by floor area ratio) and can be
quite large when located underneath the entire building footprint (PAMC Section
18.12.090). In 2015, 13 residential sites were conducting basement construction
groundwater pumping, with 12 of these sites constructing a basement as well as a
second story.
Basement construction groundwater pumping occurs when a basement is
constructed in areas of shallow groundwater, typically in the neighborhoods
closer to the bay or near former creek beds. Perimeter wells are established to
draw down the groundwater allowing for construction of the basement.
Dewatering continues until enough of the house has been constructed to keep
the basement in place. The groundwater being pumped is not potable (i.e.
drinkable). The Santa Clara Valley Water District regulates the groundwater basin
in Santa Clara County, but does not regulate incidental pumping associated with
basement dewatering.
Summary of Current Regulations
The City of Palo Alto has long regulated several aspects of basement groundwater
pumping for both residential and commercial sites. Geotechnical investigations
are required for basement construction and dewatering permits must be obtained
when groundwater is likely to be encountered and dewatering needed. The
permit is used, in part, to prevent pumping from October to April ensuring
adequate storm drain system capacity during winter months. City of Palo Alto
staff verifies that construction dewatering meets requirements for pH and
sediment prior to allowing discharge to the storm drain system, meeting State of
California stormwater regulations.
Unlike most Bay Area cities, Palo Alto does not allow drains around basement
foundations, collecting water and pumping to the storm drain continuously;
instead basements must be constructed to be waterproof.
1 In commercial and multi-family zones, basements used for parking are generally not counted towards allowable
floor area, but basement space containing usable space is. This report focuses on basements in R-1 neighborhoods
which have been the subject of most of the community concern.
City of Palo Alto Page 3
In 2008, the Planning and Transportation Commission held hearings on the
dewatering issue and a literature review prepared by EIP Associates was
presented (Attachment A).
In Summer 2014, the City’s Public Works Department (PWD) piloted a truck fill
station at a dewatering site to address public concern regarding the apparent
wasting of pumped water to storm drains during the drought. Following the
success of this first truck fill station, all basement groundwater pumping sites,
except those located in known groundwater contamination areas, were required
to install truck fill stations based on PWD specifications (Attachment B). The
stations accommodate large diameter and garden hoses as well as bucket filling.
Outreach includes dewatering sites published and mapped on the City website
(http://www.cityofpaloalto.org/gov/depts/pwd/pollution/recycled_n_other_non
_potable_water.asp), informational door hangers provided to contractors for
distribution to neighbors of the construction dewatering site (Attachment C), and
a Frequently Asked Questions document (Attachment D). Usage tracked with log
sheets showed some sites used extensively by neighboring properties, while
others saw little use. The City’s water truck utilized dewatering sites for tree and
median irrigation.
During the summer 2015 staff met with contractors to discuss additional ideas to
address public concerns. Contractors advised staff of the uniqueness of Palo Alto
in imposing standards on dewatering and requiring use of the pumped
groundwater, believing the requirements increase pumping duration and project
cost. One contractor stressed users could be injured at the fill stations, leading to
potential liability. Other than increasing public outreach, no new solutions to
decrease pumping or increase utilization of groundwater were identified.
Discussion
In Summer 2015, sites beginning the permit process were required to develop a
Use Plan to maximize the use of the pumped groundwater. Additional
requirements suggested by members of the public include a moratorium on
basements until further study is performed, more detailed review of basement
construction projects, minimizing pumping by using other methods for
dewatering or increasing weight on basement slab, requiring use of all the water
being pumped, payment for water pumped and directing water to the sanitary
City of Palo Alto Page 4
sewer. See Attachment E for correspondence from the public and Attachment F
for a petition submitted regarding the basement construction moratorium.
Using adaptive management based on learnings from this past summer, staff is
proposing to investigate the following program enhancements for basement
dewatering in 2016:
1. Encouraging greater fill station use by distributing more door-hangers and
enlisting other public outreach regarding dewatering, fill stations and trees.
This will be a contractor requirement and City activity.
2. Strengthening outreach on the water cycle and value of fresh water flows
to storm drains, creeks and bay.
3. Refining requirements for contractor Use Plans, including maximizing on-
site water use, one day per week water truck hauling service for neighbor
and City landscaping and piping to nearby parks or major users where
feasible. Contractors will be responsible for implementation of Use Plans.
4. Expanding fill station specifications to address water pressure issues
resulting from multiple concurrent users, including separate pumps for
neighbors where needed and sidewalk bridges for hoses to reduce tripping
hazards. Contractors will be responsible for implementation.
5. Broadening the City’s Basement Pumping Guidelines to specifically require
a determination of impacts of groundwater pumping on adjacent buildings,
infrastructure and trees or landscaping. Applicants would determine the
approximate location of the temporary groundwater cone of depression
caused by pumping. Avoidance measures would be required if impacts are
anticipated. Urban Forestry staff may develop guidelines for avoidance
measures such as soil enhancement and supplemental watering (by project
applicant) of neighboring landscaping. Additional measures could include
adjusting the location, depth or duration of pumping or altering
construction methods.
In addition, staff will request assistance from the Santa Clara Valley Water District
to continue to evaluate any potential effects of basement pumping on deep
City of Palo Alto Page 5
groundwater levels, particularly related to the City of Palo Alto emergency wells.
This issue is partially addressed in a previously provided 2003 report to the City by
Carollo Engineers (Attachment G). If additional actions by the City are needed,
they will be forwarded to the Policy and Services Committee prior to the 2016
construction season, along with the finalization of the above five
recommendations.
Resource Impact
Testing and refining the suggested measures to improve the dewatering program
or any other measures suggested by the Committee will require staff time that is
currently allocated elsewhere. These measures may increase basement
construction project costs.
Staff is seeking approval of Staff exploration of the named activities. One of the
elements to be explored is the amount of staff time needed for implementation,
and whether the additional time can be absorbed into existing staffing levels.
While Staff time is not expected to be large, Staff will be reporting back to the
Committee on this issue.
Environmental Review
The suggested program enhancements are minor modifications to an existing
regulatory program designed to be protective of the environment. They would be
covered by the general rule that California Environmental Quality Act (CEQA) does
not apply where there is no possibility an action could have a significant effect on
the environment (State CEQA Guidelines Section 15601(b)(3).
Attachments:
Attachment A: 2008 Planning and Transportation Division Study Session Regarding
Basement Construction Impacts (PDF)
Attachment B: New Aquifer Filling Station Specifications (PDF)
Attachment C: Doorhanger (PDF)
Attachment D: Groundwater Pumping from Building Sites FAQ (PDF)
Attachment E: Correspondence (PDF)
Attachment F: Basement Moratorium Petition (PDF)
Attachment G: Groundwater_Supply Report (PDF)
to address zoning criteria for light wells and below grade patios, but the pertinent code section is
provided and some of the issues may affect those provisions.
DISCUSSION
The discussion below summarizes recent basement construction statistics, the issues addressed in
the Public Works memo, the existing Public Works dewatering policy, potential impacts on
neighboring properties, and the use of concrete in basement construction and its implications for
the City's Green Building program. A few options for addressing public concerns are provided at
the end of the section.
Recent Basement Construction
The City's Building Division reports that there were permits for 65 new single family residential
basements issued over the past 2 years (through June 30, 2008). In that timeframe, there were a
total of 181 new single family home permits, excluding the detached condos for Sterling Park
(96 units). Ten (10) of the basements (of the total 65) were constructed for major
renovations/rebuilds. Basement construction has increased as compared to prior years, with an
average of about 22 bas.ement permits issued from 2001-2004.
The Public Works Department estimates that, of the total number of permits for basements in
recent years, approximately 5 per year require dewatering permits. In calendar year 2008 thus
far, the Department has issued 3 dewatering permits, and does not anticipate issuing any others,
given the proximity to the wet weather season. Attachment G provides a map of the depth of
groundwater in Palo Alto, as mapped by the Santa Clara Valley Water District.
June 9 Public Works Informational Memo
The June 9, 2008 Informational Memo from Public Works (Attachment A) addresses many
issues raised by the Council, Commission, and the public, including discharge volume of
dewatering, pump noise, water table impacts, subsidence, tree impacts, contaminated
groundwater migration, discharge of groundwater after basement construction, basement
excavation, and storm drain capacity. In some areas of technical impact, such as water table and
subsidence impacts, the memo refers to a study prepared by EIP Associates, Inc. in 2004
(Attachment D), which staff feels adequately addresses those specific concerns. Other concerns
regarding pump noise, contaminated groundwater contamination, and discharge of groundwater
after basement construction, are addressed in the Council memo but not discussed further here.
The discussions below focus on the key issues of discharge volumes and dewatering policy, the
impacts of basement excavation on neighboring sites, and the green building implications of
basement construction.
Discharge Volumes
The Public Works Department's "Basement Excavation Dewatering and Basement Drainage
Rules" (Attachment B) require a dewatering plan and permit for each site where dewatering
during basement construction is proposed. Groundwater levels must be identified in a
geotechnical report prior to permit review. Drawdown wells are typically installed around the
perimeter of the excavation and pump water out of the shallow aquifer to draw down the level of
the groundwater so the basement can be constructed without water filling the excavation. Public
Works estimates that draw down well systems for dewatering during basement construction can
pump approximately 30-50 gallons per minute of water non-stop for 3-6 months or more while
City of Palo Alto Page2
the basement is constructed. The rules now have been revised to limit dewatering to the months
of April through October. The total volume of water pumped into the storm drain system from a
dewatering operation is substantial, typically a few million gallons. However, the groundwater
level is re-established rapidly after dewatering ceases and the discharged water ultimately
remains within the water regime and may replenish aquifers downstream or may flow to a creek
or the Bay. Nevertheless, some water is surely lost in the process and the storm drain system is
burdened by the additional flow.
The Public Works Department's Basement Exterior Drainage Policy (Attachment C), last revised
October 1, 2006, prohibits the use of perforated pipe systems for basement drainage and requires
that all new basements be designed so that ongoing discharge after construction is not required
(with limited exceptions for basement-level exterior spaces).
The key issue for Commission discussion is whether it is appropriate to further limit or prohibit
basement construction where dewatering is required.
Impacts on Neighboring Properties
Another set of concerns about basement construction relates to potential impacts to neighboring
properties, including subsidence, effects on trees, and site stability.
• Site stability-Residents have reported concerns about the proximity ofbasement
excavation to their property line, which might result in erosion or undermining of the
property or nearby buildings. Various excavation shoring restrictions exist to protect
neighboring sites, and shoring plans are required by the Building Division. The Zoning
Code only allows basements below the main structure, so setbacks should be met, but
light wells are permitted to encroach up to 3 feet from a side property line (for a distance
of not more than 15 feet), and excavation for the basement wall may then extend to the
property line. Attachment F outlines the zoning code provisions for basements in the R-1
zone district.
• Trees -Tree impacts on the subject property or an adjacent site could occur from either
excavation damage to roots or from dewatering to a point where the roots dry out. The
Planning Arborist, however, reviews all projects to determine whether basements would
adversely impact an adjacent tree's root system, and plans would need to be revised if
impacts are identified. The Zoning Code requires that basement design would not
adversely impact any mature trees. The Planning Arborist has also noted that water
sources for most trees' roots are not as deep as the groundwater table.
• Subsidence -Staff believes that subsidence impacts, if any, are negligible from
dewatering, as the water table quickly returns to pre-dewatering levels and the duration of
dewatering is not long enough for soils to compress. Staff is aware of no demonstrated
subsidence impacts from basement construction dewatering, though some residents have
maintained that such an impact has occurred. The EIP study and contact with USGS have
also indicated negligible impact.
The key issue for Commission discussion is whether some change in policy or codes, such as a
minimum setback for excavation, would better protect neighboring properties without unduly
infringing on the potential for property owners to construct basements.
City of Palo Alto Page3
Green Building Regulations and Implications of Basement Construction
Basement construction has been identified as a "green building" issue due to the extensive
amount of energy required to produce the concrete used for basements. Concrete creates more
than 5 percent of the world's C02 emissions, at a rate of about 400 pounds of C02 for each cubic
yard of concrete (3 ,900 pounds). The cement component of concrete (7-15 % ) is the major source
of greenhouse gas emissions, and about 0.9 pound of C02 is created per pound of cement
produced, according to the Portland Cement Association. A second sustainability issue is the
amount of water discharged during dewatering during basement construction (discussed above).
The City's Green Building regulations (Attachment E) became effective on July 3, 2008. The
regulations include requirements to comply with green point rating systems for both
nonresidential (Table A) and residential (Table B) development. The definition of "square
footage" includes basement square footage, and the green points required for residential
development increase with each 70 additional square feet of house size. Thus, the ordinance does
not directly limit basement construction, but does require compensation in the form of increased
green point rating for a home with a basement. It should also be noted, however, that due to the
insulating qualities of the surrounding earth, basements are often more energy efficient than
above grade floor space.
For the Commission's information, Attachment K is an article that outlines work currently
underway by a Stanford professor to produce a "green" cement that would not only eliminate
C02 emissions from cement production, but could also use C02 emitted from other sources,
reducing those gases as well. A ways off, perhaps, but a potential solution to the adverse impacts
of concrete use in basements.
The key issue for the Commission is whether there is a basis for either limiting basement
construction or requiring further increases in green points criteria for basement construction to
minimize the carbon emissions impacts of basements.
POTENTIAL OPTIONS
Staff believes that the City's review policies generally protect neighboring properties from
deleterious effects of basement dewatering and that dewatering does not have substantial effects
on groundwater or result in the discharge of contaminated groundwater. However, water
discharge from dewatering can be substantial and there may be opportunities for the City to enact
policies or regulations to further minimize the loss of water from local sites as an enhanced
sustainability effort. Similarly, the City's Green Building regulations already require
compensation for basement construction in the form of additional green building measures to
achieve the stipulated point totals, but there may be revisions that would provide further green
building benefits where basements are constructed or to encourage retention of existing
basements in commercial areas. Some of the options available to the City may include, but are
not limited to:
1. Continuing to permit basements, with continued staff analysis of technical data and
impacts.
2. Prohibiting basement excavation within 3 feet of a low density residential property line.
City of Palo Alto Page4
3. Limiting basement construction based on the amount of water to be discharged or further
limit the timeframe for basement dewatering.
4. Modifying green building requirements to double basement square footage to determine
the number of GreenPoint Rated points required, and/ or allowing reductions for the use
of basement construction materials that reduce the embedded energy of concrete.
5. Allowing existing basements for nonresidential properties to be excluded from floor area
calculations if restricted to non-habitable uses, even ifthe basement meets Building Code
requirements for habitable space.
Subsequent to comments by the Commission, staff will return with specific recommendations for
policy or code changes to address basement issues. The Commission would then forward these
changes to Council for review and approval.
ENVIRONMENTAL REVIEW
No environmental review is required for a study session. The level of environmental review
required, if any, for potential code or policy actions will be determined once those actions are
identified.
ATTACHMENTS
A. June 9, 2008 "Basement Construction and Dewatering Impacts" Informational Memo to
City Council from Public Works Department
B. Public Works "Basement Excavation Dewatering and Basement Drainage Rules"
C. Public Works "Basement Exterior Drainage Policy," dated October 1, 2006
D. "New Basement Construction and the Groundwater Regime in Palo Alto," Technical
Memorandum prepared by EIP Associates, Inc., 2004
E. Green Building Tables for Residential and Nonresidential Development
F. Section 18.12.090 of the Zoning Ordinance re: Basements in R-1 District
G. Map of Depth to First Water, Santa Clara Valley Water District, October 15, 2003
H. May 8, 2008 E-mail from Steve Broadbent
I. July 19, 2008 E-mail from David Stonestrom
J. April 22, 2008 E-mail from Jody Davidson
K. "Green Cement May Set C02 Fate in Concrete." San Francisco Chronicle. September 2,
2008.
COURTESY COPIES
Architectural Review Board
Jody Davidson
Steve Broadbent
David Stonestrom
John Northway
Bob Morris, Public Works
REVIEWED BY: Julie Caporgno, Chief Planning and Transportation Official
DEPARTMENT/DIVISION HEAD APPROVAL: __ ~----·-~--~---· ___ _
City of Palo Alto
Curtis Williams
Interim Director
Page5
To assist Council in understanding the differences between shallow and deep aquifers _(described
·more completely in EIP's·attached report), staff provides the following descriptions.
Shallow aquifers are formed by rain seeping through the ground and pooling close to the ground
surface. The top surface of the shallow aquifer is called the water table and is typically 10-30
feet below the ground surface in most areas of Palo Alto other than the hills. This is the aquifer
that basement excavations may extend into, necessitating dewatering. Shallow aquifer water is
nonpotable. as it does not meet drinking water standards. ·
Deep aquifers are separated from the shallow aquifers by impermeable sediment layers, like rock
or clay, called aquicludes that prevent shallow aquifer water from reaching the deep aquifers. In
Palo Alto, the deep aquifers are approximately 200 feet below the ground surface. Dewatering
basement excavations has virtually no effect on the deep aquifers .
. Certain layers of permeable sediment, like sand or gravel, may trap and hold pockets of
groundwater temporarily between shallow and deep aquifers, but these are typically not affected
by basement dewatering operations. . .
Below is a brief summary of the above research organized by community key concerns.
Discharge Volume .
A soils report is required for all projects with basements or underground garages. This report
determines the depth to the shallow aquifer below the ground surface. If a contractor believes
the excavation will go into the groundwater, they will typically submit a drawdown well
dewatering plan to Public Works. Drawdown wells are· typically installed around the perimeter
of the excavation and pump water out of the shallow aquifer to draw down the level of the
groundwater so the basement can be constructed without groundwater filling the excavation.
These drawdown well systems pump approximately 30-50 gallons per minute into the storm
drain system non~stop for 3-6 months while the contractor constructs the basement.
The volume of water pumped into the storm ·drain system from a drawdown well dewatering
operation is substantial, typically a few million gallons. It could be used as landscaping water,
but it is too large a volume for individual use and too impractical to capture and reuse for other
use.
The water pumped out of the ground is discharged into the storm drains, which typically
discharge into the creeks. San Francisquito Creek is a losing creek, meaning that water is lost by
seeping through the creek bed and into the shallow aquifers. So, in this case, water pumped out
of the shallow aquifers is added back to it. For water pumped into lined creeks, the water flows
to the bay and is lost to the aquifer.
The volume of groundwater pumped out of an excavation site is a small fraction of the . total
volume of the aquifer and does not deplete or lower the aquifer, except, of. course, in the
immediate vicinity of the excavation. The USGS reports that due to natural (rain) and manmade
(irrigation, leaking sewer pipes, and the SCVWD's groundwater recharge program) methods,
more water is recharged into the shallow aquifers than is pumped out of it by all pumping in the
Santa Clara Valley. The EIP report also confirmed that the water table is only drawn down
CMR:266:08 Page 2of5
locally (within tens of feet of the excavation) and· reestablishes itself quickly after dewatering
ceases. Therefore,the cumulative effect ofdewatering on the shallow aquifers is negligible.
Pump Noise
Dewatering pumps can make excessive noise if installed improperly, and this is a concern for
neighboring residents since the pumps run 24 hours a day. Public Works is tightening the
requirements for pump operation to eliminate this problem.
Water Table Impacts
While the City currently prohibits basements in flood zones, there is no blanket prohibition
against construction in areas with shallow aquifers. Basements are not typically constructed so
deep that they actually go into the water table, but they do ·in some cases. In other cases, the
water table might rise up, as at the end of a particularly wet winter, and surround a basement.
However, in these cases, the water table level and the flow of the groundwater are not changed
due to the presence of basements, as reported by EIP.
Subsidence
Land settlement, or·subsidence, caused by temporary (such as 6 months) construction dewatering
is negligible, as reported by EIP and USGS. For subsidence to occur, dewatering needs to occur
over a number of years.
Tree Impacts Relative to Water Table Changes
The Planning ·Division arborist reports that in most of the developed areas · of Palo Alto the
preponderance of absorbing tree roots are not . found in lower soil horizon levels below seven
feet Therefore, the majority of temporary dewatering projects are not expected to impact trees.
If a tree's roots are however deep enough and have been determined, on the basis of a certified
arborist report or other ·qualified assessment, to be dependent· on the water table, theri the
mitigation would be for the , contractor to provide separate irrigation for the tree( s) during the
dewatering period.
Contaminated Groundwater Migration
Citizens have expressed a concern that large volumes of groundwater being pumped out of the
aquifers might cause nearby contaminated groundwater plumes to migrate towards the pumping
site. When an application is submitted, staff checks dewatering sites against known
contaminated groundwater plume maps. If a site is within a certain proximity to a known plume,
staff requires the water to . be tested for contaminants prior to and during discharge. The
contractor must retain an independent testing service, test for the contaminants Public Works
specifies, and submit those results to Public Works. If the water is contaminated, as it was in one
case near the Stanford Research Park superfund site, it must be treated before it can be released
or discharged to the sanitary sewer under permit from Public Works. The CRWQCB is drafting
requirements for contractors to test groundwater discharged to the storm drain system. Staff
awaits the adopted version of these requirements, scheduled for this summer, and will implement
them at that time. To date, there has been no evidence that contaminated groundwater has been
discharged into the storm drain system or that contaminated groundwater plumes have migrated.
CMR:266:08 Page 3of5
Discharge of Groundwater after Basement Construction
A few years ago, Public Works allowed the use of perforated drain pipes to be installed behind
basement walls and under basement slabs when the geotechnical engineer reported that
groundwater would not ri.se to the level of. these pipes. The pipes are installed . to .capture
rainwater that filters through the ground and collects behind basement walls in order to minimize
the chance of the water leaking through the walls. The pipes drain, to a sump where a pump then
.. pumps the water to the street gutter.· Unfortunately, after some wet. winters, groundwater did rise
up to these pipes and was then pumped c~mtinuously into the street gutter for long periods of
time, creating a number of public nuisance and safety concerns. Accordingly, Public Works
adopted a policy two years ago that prohibits the use of perforated drain pipes· for basements in
areas of the City with relatively high groundwater (east of Foothill Expressway) to eliminate
•these potential nuisances. Public Works also re.commends that applicants for. new basement
projects retain a waterproofing consultant to ensure tile basement does riot leak. .
Older basements that were permitted with perforated drain pipes still may occasionally discharge
groundwater into the street gutter. Public Works addresses these cases by working with the
homeowners to eliminate the discharge, typically accomplished by having the homeowner raise
the pump in the sump above the level of the groundwater.
Basement Excavation
Some residents have expressed a concern that the excavation pit for a basement comes too close
to adjacent properties, potentially jeopardizing the stability of these properties. Although this
strictly does not relate to dewatering, staff recognizes it as a legitimate concern. As previously
mentioned, the Building Division requires geotechnical reports for all projects that involve
basements or underground structures. · A standard feature of these ·reports is recommendations
. artd requirements from the geotechnical engineer that specify measures . to stabilize ·the
excavation during construction. The Building Division inspects all basement construction to
ensure conformance with the geotechnical report and to .verify all recommended stabilization
measures are implemented. In addition, Building Inspectors will require the contractor to install
extra precautionary measures before work can continue.
Storm Drain Capacity
Staff is concerned that dewatering basement excavations. may take. up too much capacity in the
City's storm drain pipes, minimizing the system's ability to accommodate storm water and
potentially causing or exacerbating flooding. This is not a concern raised by citizens, nor has
there been any incidents where dewatering has caused flooding, but staff is developing some
guidelines for wintertime dewatering in an effort to avoid a problem. The draft guidelines
currently disallow dewatering during the winter unless an exemption is granted by the Director
of Public Works.
CONCLUSION
Staff has researched and analyzed each of the concerns about dewatering raised by citizens.
Based on that research, staff believes that the cumulative effects of dewatering · basement
excavations has minimal impacts on the City and that the practice should be allowed to continue.
The attached EIP report essentially comes to the same conclusion. The number of residential
basements permitted in the City has increased from approximately 20 a year at the start of the
decade to approximately 30 a year currently. However, Public Works only issues about 5-10
CMR:266:08 Page 4 of 5
. E. JJl ..
~"fJ: !2~·· ••• ••.
. ~ . . .· . . .· .,.....__
ATTACHMENT A
A S S 0 .C l A T t:: S
Draft Technical Memorandum: Correlation between New Basement
Construction and the Groundwater Regime in Palo Alto, California
lo ·Statement of the Plannjng and Transportation Commission's
concerns.·
At the 14 J anua1y 2004 Commission meeting, the planning staff presented a number of
. .
proposed changes to the existing regulation of basements in the R-1 zones. During the
ensuing discussion, several Commission members expressed conc~rns about the impact of
basement construction on groundwater levels and flow directions. Eight specific,
interrelated issues were identified.
II
· 111
II
II
Is groundwater pumping causing or contributing to land subsidence?
What are the effects of pumping for months to dewater a basement constmction
site?
Are basements bemg permitted in some inappropriate areas [where the water
table is only a few feet below the ground surface], creating the need for
continuous pumping?
What groundwater effects occur if water is withdrawn from the water table and
pumped into the sewers or creeks? ·
• . What groundwater diversion effects occur if basement walls are built along
•
•
•
creeks and/or perforate aquifers? ·
What are the effects on landowners adjacent to, and down gradient from,
pumping sties? ·
What are the cumulative effects of basements on the groundwater regime?
Can basement regulations be crafted to address the hydro-geology of specific
building sites? · .
The general concern underly.iiig these issues was expressed by Commissioner
Annette Bailson: the Commission does not have the information needed to identify whether
these are issues of concern, or to make informed decisions on the issues. The remainder of
this technical memorandum seeks to respond to that underlying concern by provide some
background information about the listed issues and about groundwater hydrology of the City
relative to the constmction of basements.
Page 1of7
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1.;'·,.':·, .. ,
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. 'II''' ' 1' ·'·
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2. Differences. between shallow (surface) and deep (confined) .
groundwater aquifers.
· Defining the Aquifers
An aquiferis a body of geologic material, usually rock or some mixture of gravel, sand, silt
and clay, that is sufficiently permeable to conduct groundwater. Some definitions include
the stipulation that the body produce an economically significant flow of water before it may
be considered an aquifer. For the purposes of this technical memorandum, the broader
. .
definition is applied to allow for easier discussion ofthe water-bearing formations underlying
the City.
Of the various types of aquifers, two are of particular interest in this discussion: the shallow
or surface aquifer, and the deep or confined aquifer. The relative terms 'shallow' and 'deep'
refer to the depth of the aquifer below the surface of the ground (usually expressed as
'number of feet bgs' in hydrology studies).
A surface aquifer is so named because it is open to the surface of the ground. Rain falling
on the ground surface seeps through the soil (infiltration) to some depth where it pools to
form a more or less continuous body of water occupying the spaces between sediment
particles or rock fragments (groundwater). The top of this body of groundwater is the water
table. In the Santa Clara Plain, which forms the lowlands of Palo Alto, the water table
occurs at depths of as little as ten feet below the ground surface.
Being open to the surface of the ground, the surface aquifer is subject to the influertces of
overlying land cover and land uses. Modern stream channels, such as the numerous reaches
of San Francisquito Creek, intersect or overlie the surface aquifer, extracting water from it or
adding water to it. Paving and construction create artificially impermeable surfaces that
prevent local direct infiltration to the surface aquifer. Cherriical constituents in urban and
agricultural runoff enter the surface aquifer through infiltration from channels or detention
basins, lowering the quality of the groundwater. Leaking landfill cells, leaking underground
stornge tanks, and liquid spills also contribute to the reduction of water quality in the surface
aquifer. Although current stewardship has slowed water quality deterioration, the surface
aquifer still cannot be used as a source of potable water.
A confined aquifer is one tha.t is separated hydrologically from the overlying and underlying
sediments and rock and from other aquifers. Usually the separating agent (called an
aquiclude) is formed by a layer of impermeable sediment, such as clay, or by iffipermeable
. rock, such as unfractured granite. The confined aquifer is not connected directly to the
overlying ground surface and is separated from the surface aquifer by an aquiclude. It is, in
effect, a separate hydrologic system, gaining water from_ some distant source (i.e., not local
Page 2of7
'1.·,'···','',,.,
11 1 I I
I . :,j1•11 I
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/\SSOC!AlES
rainfall). and transmitting it to some other relatively distant discharge area. Bec.:ause the
.. confined·aquifer is ·below, and hydrologically separated from; the surface aquifer, it is, by
definition, a deep aquifer, irrespective of the number of feet it is below the ground surface.
Several aquifers tnay underlie each other. This is the case beneath the Santa Clara Plain
where geologically recent stream-hid (alluvial) gravel, sand, silt, and clay form a sequence of
· deposits nearly 1500 feet thick between the foothills of the Coast Ranges and San Francisco
. .
Bay. Channels of ancient rivers depositing this material have been cut off and filled by
succeeding intersecting channels, which, in turn, have been buried by the deposits of more
modern channels. In this way a complex series of sediment layers of unconsolidated
(loose), partially consolidated (dense), and consolidated (very dense) material has been built
up as the Santa Clara Plain~ The layers are discontinuous and of greater or lesser
permeability, depending on their density and clay of silt content.
A complicating factor in examining such a series of aquifers is that often they are not
completely confined. The aquicludes separating the aquifers may not be totally impermeable
(in which case· they are called aquitards). allowing water to seep from one aquifer to another.
The aquifers may be connected within or outside the local area, arising from a common
source or flowing to a common discharge area. The aquifers may be connected artificially
through leaks in wells or along pilings passing through the aquifers. Beneath the portion of
the Santa Clara Plain in Palo Alto, there is a confining clay layer that separates the surface
aquifer from the deeper aquifers, but, on a regional level, this separation attenuates and,
eventually, disappears farther south in San Jose ..
Being separated from the surface aquifer in this part of the Santa Clara Plain, the confined
aquifers beneath the City are not subject to the. direct influences previously described for
land cover and land uses above the surface aquifer. To the extent that groundwater migrates
from the southern part of the Santa Clara Plain groundwater basin to the northern part, the
effects of similar land cover and land uses in areas toward San Jose may affect water quality
in the deep aquifers beneath Palo Alto.
Construction-period Dewatering Effects
. In general, cons~ction-period dewatering effects are limited to the surface aquifer. This
would not necessarily be the case for major high-rise construction where foundations and
below-grade levels may extend 100 or more feet beneath the ground surface, increasing the
. chances of encountering confined aquifers. It is, however, the case for the type of
relatively shallow basement construction being considered in the Zoning Ordinance Update.
. In the Santa Clara Plain portion of Palo Alto, the uppermost sequence of unconsolidated
and partially consolidated alluvium is about 200 feet thick. This sequence contains the
Page 3of7
ASSOCJJ,TES
surface aquifer~ the base of which is the previously mentioned clay aquiclude identified by
the Santa Clara Valley Water District (SCVWD) in its 2001 Groundwater Management Plan.
The general direction of groundwater flow in this area is northeast toward the Bay, so the
surface aquifer and_ the _deeper, confined aquifers tend to remain separated in Palo Alto until
they reach the vicinity of the Bay margin.
The removal of groundwater from an excavation during below-ground-level construction is
necessary to provide safety for the construction workers, and .is a prerequisite for
wate1proofing the building's foundation and subsurface floors. One method for
accomplishing this is to dig a small pit below the base of the foundation excavation, slope
the excavation so groundwater drains to the pit, and then pump the water out of the pit and
into the storm drainage system .. Another method is to drill temporary wells around the
building footprint and pump directly from the groundwater body to the storm drainage
system until the local water table drops below the base of the excavation. In either case,
groundwater flowing into the area of drawdowrt created by the dewatering process is
deflected toward the base of the excavation, whence it is pumped to the storm drainage
system. Groundwater beyond the influence of the dewatering process continues to flow
normally.
Dewatering pumping continues until the foundation and subsmface floors are completed
and the excavation is filled. The amount of water deflected depends on the level of the
water table, the permeability of the material adjacent to the excavation, and the length of
time th~ excavation needs to be kept open and dry. An increase in any of these factors ·
increases the amount of water deflected. This amount is small when compared to the total
volume of available groundwater directly beneath the Santa Clara Plain (see below). Because
the deflection is temporary and very localized, and because groundwater levels at the sites
recover rapidly once pumping has ceased, there appears to be no discernable long-tetm
effect on the surface aquifer.
In the areas adjacent to the site being dewatered, the water table would be lowered
temporarily by the dewatering process. This effect could extend from several feet to several
tens of feet beyond the excavation depending on ·the method used, the level of the water
table at the time dewatering began, the permeability of the material adjacent to the
excavation, and the length of time the excavation needed to be kept open and dry. The
possibility exists that adjacent landscaping could be experience deterioration from reduced
·groundwater availability.
Defleetion or Reduction of the rate of Groundwater Flow
Although the amount of water pumped from an excavation may appear substantial as it
Page 4of7
A ·s S () C l A l · E S.
flows along a street to a storm drain inlet, it is small compared to the amount of
groundwater directly beneath the Santa Clara Plain. The _SCVWD's current estimate is that
there is more than 350,000 acre-feet of groundwater available in the Santa Clara Sub basin .
. An excavation dewatering flow of 1 cubic foot per second would deflect 1.98 acre-feet of
· water per day. Because groundwaterwoUld be pumped out of the excavation faster than ·
could flow in, the ~~teration in groundwater flow rate would be less than the rate of
de\Vatering. Because t.he resultant groundwater flow ~eflectionis temporary; small, and very
localized, there appears to be no discernable long.oterm effect on the ·surface aquifer.
. .
Because dewatering for basement construction occurs only in the uppermost portion of the
surface aquifer, there would be no effect on the deep aquifer.
. . ..
In a typical 3-month excavation period tlie 1.98 acre:. . .feet per day dewatering flow would
amount to 0.05% (one-twentieth of one percent) of the minimum known groundwater
resource in the subbasin. No published information about the subbasin's water budget has
been found; so any to attempt to predict how quickly the watet would be replaced through
recharge would be speculative. It is known, however, that the importation of potable water
and the SCVWD controlled recharge program have assisted groundwater levels in the
sub basin to rise 200 feet during the last 40 years. Most of that rise has been in the surface
aquifer. The implication is that the subbasin is being recharged at a rate substantially higher
than the rate of withdrawal from all pumping, including dewatering for basement
construction. Consequently,it appears that the amount of flow from one, or even several,
dewatering operations would not have long-term effects on the surface aquifer.
In the.areas adjacent to the site beingdewatered, the rate and flow directions of the
groundwater would be altered temporarily by the dewatering process. Groundwater in the
influenced area would move toward the base of the excavation at a rate lower than the rate
.·of dewatering discharge. This effect could extend from several feet to several tens of feet
. beyond the excavation depending on the method used, the level of the water table at the
time dewatering began·,· the permeability of the material adjacent to· the excavation, and the
length of time the excavation needed to be kept open and dry. Flow directions and rates
would revert to near normal when dewatering ceased.
There would be some displacement of groundwater flow around the newly constructed
. basement, depending on the permeability of the surrounding soil materials. The volume of
space displaced by the basement could be several thousand to severai tens of thousands of
cubic feet, which, although small-compared to the volume of the surface ~quifer, could be
significant locally, especially if there were other similarly sized basements in the immediate
vicinio/. The flow of groundwater would readjust to this condition, possibly altering the
level of the water table in the vicinity of the site for· several weeks or months, but is unlikely
to experience any major permanent change. The groundwater level in the surface aquifer
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ASSOCJATES
undergoes more significant changes during the rainy season than would be expected from
long-term flow deflection caused by basements.
Saltwater Intrusion and Subsidence
Saltwater intrusion and subsidence in the Santa Clara Subbasin are documented regional
effects of the excessive removal of groundwater from the deep aquifer (overdrafting) o~er
. many years. This practice was curtailed in the mid-1960s when the importation of potable
·water increased substantially. Smee then, the SCVWD has been recharging the subbasin
thereby raising groundwater levels, impeding saltWater infiltration of the sutface aquifer,
and virtually eliminating further overdraft-related subsidence (the effects of previops ·
subsidence cannot be reversed because portions of the deep aquifer have been compressed
permartently). Such basin-wide effects could recur only if the deep aquifer became
overdrafted again. Because dewatering for basement construction occurs only in the.
uppermost portion of the surface aquifer and involves only a small amount of groundwater
withdrawal, no effects would occur in the deep aquifer.
3. Palo Alto Public Works Department existing regulatory structure.
There are a number of policies in place that provide protection for the City's groundwater
resource and for property owners in the vicinity of new basement construction.
•
•
•
•
•
The PublicWorks Department prohibits the long-term pumping ofgroundwater
after a basement has been constructed. This eliminates the possibility that the
w~ter ·table in the vicinity of the project would be lowered permanently.
The Public W or.ks Department requires basements to be waterproofed and
strengthened structurally below the expected groundwater level. This eliminates
the need for groundwater pumping.
The Public Works Department requires permit applicants whose projects would
have basements to prepare a geotechnical investigation and report that would
determine, among other information, the expected highest groundwater level in
the local shallow aquifer. This allows the department to make informed
decisions about the advisability of basement construct:lon at a particular site
and/ or to _set the conditions under which basement construction may proceed.
If dewatering is necessary for basement construction, the Public Works
Department sets the dewaterillg permit conditions based on the hydrology of the
specific site under consideration. This ensures resource and property protection
where it is needed.
The Public Works Department allows the removal of seepage water that collects
along basement walls above the water table. Normally this removal would need
only a minimal amount of pumping, but may need-to be monitored.
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4. Recommendation regarding the advisability of codifying groundwater
effects in the Zoning O_rdinance Update ·
The above-listed Public Works Department policies dealing with basement construction and
dewate:ring for such·constiuction are intended to prevent.substantial impacts to
groundwater, either on an area-wide basis or in the vicinity of the construction site.
Although the policies and their associated construction standards appear to address the . . . .
issues adequately, it may be advisable for the Public Works Pepartmerit to increase the
community's awareness of these issues through an out-reach program .. Because these issues
are, essentially, engineering concerns that are site-specific and already covered by existing
regulations, there is no need to modify the zoning ordinance with respect to them.
Sincerely,
George J. Burwasser,
EIP Associates
EIP ASSOCIATES 353 SACRAMENTO STREET SUITE 1000 SAN FRANCISCO, CALIFORNIA 94111
Telephone 415-362~ 1500 Facsimile 415-362-1954 E-mail .rf@eipas.wdaies.com
JJJ/ll/V.eipassodales.com
ATTACHMENT B
BASEMENT EXCAVATION DEWATERING
AND BASEMENT DRAINAGE RULES
BASEMENT DRAINAGE: Due to high groundwater throughout much of the City and
Public Works prohibiting the pumping and discharging of groundwater, perforated
pipe drainage systems at the exterior of the basement walls or under the slab are
not allowed for this site. A drainage system is, however, required for all exterior
basement-level spaces, such as lightwells, patios or stairwells. This system consists
of a sump, a sump pump, a backflow preventer, and a closed pipe from the pump to
a dissipation device onsite at least 10 feet from the property line, such as a bubbler
box in a landscaped area, so that water can percolate into the soil and/or sheet flow
across the site. The device must not allow stagnant water that could become
mosquito habitat. Additionally, the plans must show that exterior basement-level
spaces are at least 7" below any adjacent windowsills or doorsills to minimize the
potential for flooding the basement. Public Works recommends a waterproofing
consultant be retained to design and inspect the vapor barrier and waterproofing
systems for the basement.
BASEMENT SHORING: Shoring for the basement excavation, including tiebacks,
must not extend onto adjacent private property or into the City right-of-way without
having first obtained written permission from the private property owners and/or an
encroachment permit from Public Works.
DEWATERING: Basement excavations may require dewatering during construction.
Public Works only allows groundwater drawdown well dewatering. Open pit
groundwater dewatering is disallowed. Dewatering is only allowed from April
through October due to inadequate capacity in our storm drain system. The
geotechnical report for this site must list the highest anticipated groundwater level.
We recommend a piezometer to be installed in the soil boring. The contractor must
determine the depth to groundwater immediately prior to excavation by using the
piezometer or by drilling an exploratory hole if the deepest excavation Will be within
3 feet of the highest anticipated groundwater level. If groundwater is within 3 feet
of the deepest excavation, a drawdown well dewatering system must be used, or
alternatively, the contractor can excavate for the basement and hope not to hit
groundwater, but if he does, he must immediately stop all work and install a
drawdown well system before he continues to excavate. Public Works may require
the water to be tested for contaminants prior to initial discharge and at intervals
during dewatering. If testing is required, the contractor must retain an independent
testing firm to test the discharge water for the contaminants Public Works specifies
and submit the results to Public Works.
Public Works reviews and approves dewatering plans as part of a Permit for
Construction in the Public Street ("street work permit"). The applicant can include a
dewatering plan in the building permit plan set in order to obtain approval of the plan
during the building permit review, but the contractor will still be required to obtain a
street work permit prior to dewatering. Public Works has a standard dewatering plan
sheet that can be used for this purpose and dewatering guidelines are available on
Public Works' website. Alternatively, the applicant must include the above
dewatering requirements in a note on the site plan.
Attachment C
PUBLIC WORKS ENGINEERING
BASEMENT EXTERIOR DRAINAGE POLICY
EFFECTIVE OCTOBER 1, 2006
The Department of Public Works (Public Works) will not permit the use of basement exterior
drainage systems consisting of perforated pipes located on the exterior of the basement walls or
underneath the slab that collect water which is then pumped to the surface of the ground for
discharge, either on-site or off-site, for all City of Palo Alto parcels northeast (the bay side) of
Foothill Expressway.
Purpose
To ensure the public safety and health by preventing the discharge of groundwater into the City
gutter system. The discharge of groundwater into the gutter system causes the following public
safety, health and nuisance concerns:
• gutters are constantly wet and may enhance the growth of algae, thereby creating a
slippery condition for pedestrians, bicyclists and motorists
• ponded water at the low spots of the gutter may be slippery to cross for pedestrians,
bicyclists and motorists
• ponded water in the gutter may become mosquito habitat
• ponded water in the gutter may seep through cracks, undermining the subgrade and
degrading the gutter and adjacent pavement
• groundwater discharge into the City's storm drain system adversely affects others
who need to discharge storm water run-off for which the system was designed
Background
In the past, Public Works allowed perforated pipe basement drainage systems to collect water
behind basement walls and under basement slabs and discharge it at the ground. Architects
proposed these systems in order to minimize the chances of water leakage through the basement
walls and slabs. These systems were permitted with the intention of only collecting and
discharging small amounts of rainwater that had seeped down through the soil. For proposed
basement drainage systems, Public Works required geotechnical reports that estimated the
highest expected groundwater level at the site and Public Works required that the perforated
pipes be placed above this level. Recent experience indicates that oftentimes the groundwater
level rose above the estimated level and entered the perforated pipes, resulting in the constant
pumping of groundwater into the street gutter.
Analysis
Public Works has obtained a groundwater elevation contour map from the Santa Clara Valley
Water District. These maps were established using data from numerous water monitoring wells
the SCVWD maintains throughout the City. The contours are the depth below ground to the
highest level the main groundwater aquifer has risen to since the monitoring wells were installed.
The area of town where there is relatively high groundwater (above 20 feet below-grade) is
roughly northeast of Foothill Expressway.
The main aquifer depicted in the contour map is not the only source of groundwater. Due to soil
properties, groundwater can get trapped between two relatively impermeable layers of soil.
These lenses of perched groundwater can occur essentially anywhere and be of any size.
Consequently, even though the SCVWD map may indicate a certain area of town has
groundwater at 20 feet below-grade, for instance, there may currently be perched water closer to
the surface or perched water may occur in the future closer to the surface.
Summary
Public Works feels that the public safety and health, potential nuisance, and maintenance
concerns caused by the discharge of groundwater into street gutters outweigh the developers'
desire for perforated pipe drainage systems. Although certain sites may seem appropriate for
perforated pipe drainage systems because of current low groundwater levels, higher groundwater
levels may occur in the future. Accordingly, Public Works will no longer permit perforated pipe
basement drainage systems installed in order to discharge water at the ground surface northeast
of Foothill Expressway.
Drainage systems are required and will be permitted for basement-level exterior spaces, such as
stairwells, lightwells and patios. These drainage systems consist of a sump, a sump pump, and a
closed pipe from the pump to a dissipation device onsite, such as a bubbler box in a landscaped
area, so that water can percolate into the soil and/or sheet flow across the site. The device must
not allow stagnant water to occur that could become mosquito habitat. Additionally, the plans
must show 8" of freeboard between the floor of any exterior basement-level space and any
adjacent windowsills or doorsills.
Glenn Roberts, Director of Public Works
S:PWD/ENG/TYPING/Morris/Development/Basement Drainage/Basement Drainage Policy
ASSOCIATES
2. Differences between shallow (surface) and deep (confined)
groundwater aquifers.
Defining the Aquifers
An aquifer is a body of geologic material, usually rock or some mixture of gravel, sand, silt
and clay, that is sufficiently permeable to conduct groundwater. Some definitions include
the stipulation that the body produce an economically significant flow of water before it may
be considered an aquifer. For the purposes of this technical memorandum, the broader
definition is applied to allow for easier discussion of the water-bearing formations underlying
the City.
Of the various types of aquifers, two are of particular interest in this discussion: the shallow
or surface aquifer, and the deep or confined aquifer. The relative terms 'shallow' and 'deep'
refer to the depth of the aquifer below the surface of the ground (usually expressed as
'number of feet bgs' in hydrology studies).
A surface aquifer is so named because it is open to the surface of the ground. Rain falling
on the ground surface seeps through the soil (infiltration) to some depth where it pools to
form a more or less continuous body of water occupying the spaces between sediment
particles or rock fragments (groundwater). The top of this body of groundwater is the water
table. In the Santa Clara Plain, which forms the lowlands of Palo Alto, the water table
occurs at depths of as little as ten feet below the ground surface.
Being open to the surface of the ground, the surface aquifer is subject to the influences of
overlying land cover and land uses. Modern stream channels, such as the numerous reaches
of San Francisquito Creek, intersect or overlie the surface aquifer, extracting water from it or
adding water to it. Paving and construction create artificially impermeable surfaces that
prevent local direct infiltration to the surface aquifer. Chemical constituents in urban and
agricultural runoff enter the surface aquifer through infiltration from channels or detention
basins, lowering the quality of the groundwater. Leaking landfill cells, leaking underground
storage tanks, and liquid spills also contribute to the reduction of water quality in the surface
aquifer. Although current stewardship has slowed water quality deterioration, the surface
aquifer still cannot be used as a source of potable water.
A confined aquifer is one that is separated hydrologically from the overlying and underlying
sediments and rock and from other aquifers. Usually the separating agent (called an
aquiclude) is formed by a layer of impermeable sediment, such as clay, or by impermeable
rock, such as unfractured granite. The confined aquifer is not connected directly to the
overlying ground surface and is separated from the surface aquifer by an aquiclude. It is, in
effect, a separate hydrologic system, gaining water from some distant source (i.e., not local
Page 2of7
ASSOClATlr:S
surface aquifer, the base of which is the previously mentioned clay aquiclude identified by
the Santa Clara Valley Water District (SCVWD) in its 2001 Groundwater Management Plan.
The general direction of groundwater flow in this area is northeast toward the Bay, so the
surface aquifer and the deeper, confined aquifers tend to remain separated in Palo Alto until
they reach the vicinity of the Bay margin.
The removal of groundwater from an excavation during below-ground-level construction is
necessary to provide safety for the construction workers, and is a prerequisite for
waterproofing the building's foundation and subsurface floors. One method for
accomplishing this is to dig a small pit below the base of the foundation excavation, slope
the excavation so groundwater drains to the pit, and then pump the water out of the pit and
into the storm drainage system. Another method is to drill temporary wells around the
building footprint and pump directly from the groundwater body to the storm drainage
system until the local water table drops below the base of the excavation. In either case,
groundwater flowing into the area of drawdown created by the dewatering process is
deflected toward the base of the excavation, whence it is pumped to the storm drainage
system. Groundwater beyond the influence of the dewatering process continues to flow
normally.
Dewatering pumping continues until the foundation and subsurface floors are completed
and the excavation is filled. The amount of water deflected depends on the level of the
water table, the permeability of the material adjacent to the excavation, and the length of
time the excavation needs to be kept open and dry. An increase in any of these factors
increases the amount of water deflected. This amount is small when compared to the total
volume of available groundwater directly beneath the Santa Clara Plain (see below). Because
the deflection is temporary and very localized, and because groundwater levels at the sites
recover rapidly once pumping has ceased, there appears to be no discernable long-term
effect on the surface aquifer.
In the areas adjacent to the site being dewatered, the water table would be lowered
temporarily by the dewatering process. This effect could extend from several feet to several
tens of feet beyond the excavation depending on the method used, the level of the water
table at the time dewatering began, the permeability of the material adjacent to the
excavation, and the length of time the excavation needed to be kept open and dry. The
possibility exists that adjacent landscaping could be experience deterioration from reduced
groundwater availability.
Deflection or Reduction of the rate of Groundwater Flow
Although the amount of water pumped from an excavation may appear substantial as it
Page 4of7
ASSOCIATES
flows along a street to a storm drain inlet, it is small compared to the amount of
groundwater directly beneath the Santa Clara Plain. The SCVWD's current estimate is that
there is more than 350,000 acre-feet of groundwater available in the Santa Clara Subbasin.
An excavation dewatering flow of 1 cubic foot per second would deflect 1.98 acre-feet of
water per day. Because groundwater would be pumped out of the excavation faster than
could flow in, the alteration in groundwater flow rate would be less than the rate of
dewatering. Because the resultant groundwater flow deflection is temporary, small, and very
localized, there appears to be no discernable long-term effect on the surface aquifer.
Because dewatering for basement construction occurs only in the uppermost portion of the
surface aquifer, there would be no effect on the deep aquifer.
In a typical 3-month excavation period the 1.98 acre-feet per day dewatering flow would
amount to 0.05% (one-twentieth of one percent) of the minimum known groundwater
resource in the subbasin. No published information about the subbasin's water budget has
been found, so any to attempt to predict how quickly the water would be replaced through
recharge would be speculative. It is known, however, that the importation of potable water
and the SCVWD controlled recharge program have assisted groundwater levels in the
subbasin to rise 200 feet during the last 40 years. Most of that rise has been in the surface
aquifer. The implication is that the subbasin is being recharged at a rate substantially higher
than the rate of withdrawal from all pumping, including dewatering for basement
construction. Consequently, it appears that the amount of flow from one, or even several,
dewatering operations would not have long-term effects on the surface aquifer.
In the areas adjacent to the site being dewatered, the rate and flow directions of the
groundwater would be altered temporarily by the dewatering process. Groundwater in the
influenced area would move toward the base of the excavation at a rate lower than the rate
of dewatering discharge. This effect could extend from several feet to several tens of feet
beyond the excavation depending on the method used, the level of the water table at the
time dewatering began, the permeability of the material adjacent to the excavation, and the
length of time the excavation needed-to be kept open and dry. Flow directions and rates
would revert to near normal when dewatering ceased.
There would be some displacement of groundwater flow around the newly constructed
basement, depending on the permeability of the surrounding soil materials. The volume of
space displaced by the basement could be several thousand to several tens of thousands of
cubic feet, which, although small compared to the volume of the surface aquifer, could be
significant locally, especially if there were other similarly sized basements in the immediate
vicinity. The flow of groundwater would readjust to this condition, possibly altering the
level of the water table in the vicinity of the site for several weeks or months, but is unlikely
to experience any major permanent change. The groundwater level in the surface aquifer
Page 5of7
ASSOCIATES
undergoes more significant changes during the rainy season than would be expected from
long-term flow deflection caused by basements.
Saltwater Intrusion and Subsidence
Saltwater intrusion and subsidence in the Santa Clara Subbasin are documented regional
effects of the excessive removal of groundwater from the deep aquifer ( overdrafting) over
many years. This practice was curtailed in the mid-1960s when the importation of potable
water increased substantially. Since then, the SCVWD has been recharging the subbasin
thereby raising groundwater levels, impeding saltwater infiltration of the surface aquifer,
and virtually eliminating further overdraft-related subsidence (the effects of previous
subsidence cannot be reversed because portions of the deep aquifer have been compressed
permanently). Such basin-wide effects could recur only if the deep aquifer became
overdrafted again. Because dewatering for basement construction occurs only in the
uppermost portion of the surface aquifer and involves only a small amount of groundwater
withdrawal, no effects would occur in the deep aquifer.
3. Palo Alto Public Works Department existing regulatory structure.
There are a number of policies in place that provide protection for the City's groundwater
resource and for property owners in the vicinity of new basement construction.
•
•
•
•
•
The Public Works Department prohibits the long-term pumping of groundwater
after a basement has been constructed. This eliminates the possibility that the
water table in the vicinity of the project would be lowered permanently.
The Public Works Department requires basements to be waterproofed and
strengthened structurally below the expected groundwater level. This eliminates
the need for groundwater pumping.
The Public Works Department requires permit applicants whose projects would
have basements to prepare a geotechnical investigation and report that would
determine, among other information, the expected highest groundwater level in
the local shallow aquifer. This allows the department to make informed
decisions about the advisability of basement construction at a particular site
and/ or to set the conditions under which basement construction may proceed.
If dewatering is necessary for basement construction, the Public Works
Department sets the dewatering permit conditions based on the hydrology of the
specific site under consideration. This ensures resource and property protection
where it is needed.
The Public Works Department allows the removal of seepage water that collects
along basement walls above the water table. Normally this removal would need
only a minimal amount of pumping, but may need to be monitored.
Page 6of7
attained the compliance threshold as indicated for the Covered Project type as set
forth in the Standards for Compliance outlined in Section 18.44.040.
(u) "Single-family or two-family residential" means a single detached dwelling unit or
two units in a single building.
(v) "Square footage," for the purposes of calculating commercial, multi-family
residential, and single-family and two-family new construction square ·footage, means
all new and replacement square footage, including basement areas (7 feet or greater in
height) and garages, except that unconditioned garage space shall only count as 50%
of that square footage. Areas demolished shall not be deducted from the total new
construction square footage.
(w) "Threshold Verification by LEED AP" means verification by a LEED accredited
professional certifying that each LEED checklist point listed was verified to meet the
requirements to achieve that· point. The LEED AP shall provide supporting
information from qualified professionals (e.g. civil engineer, electrical eng~neer, Title
24 consultant, commissioning agent, etc.) to certify compliance with each point on
the checklist. Documentation of construction consistent with building plans
calculated to achieve energy compliance is sufficient verification in lieu of post-
construction commissioning.
18.44.040 Standards for Compliance.
The City Council shall establish by resolution, and shall periodically review and update
as necessary, Green Building Standards for Compliance. The Standards for Compliance shall
include, but are not limited to, the following:
(a) The types of projects subject to regulation (Covered Projects);
(b) The green building rating system to be applied to the various types of projects;
( c) Minimum thresholds of compliance for various types of projects; and
( d) Timing and methods of verification of compliance with these regulations.
The Standards for Compliance shall be approved after recommendation from the Director
of Planning and Community Environment, who shall refer the Standards for recommendation by
the Architectural Review Board, prior to Council action.
18.44.050
(a)
080604 syn 6050410
Incentives for Compliance.
In addition to the required standards for compliance, the City Council may,
through ordinance or resolution, enact financial, permit review process, or zoning
incentives and/or award or recognition programs to further encourage higher
levels of green building compliance for a project.
6
ATTACHMENT F
18.12.090 Basements
Basements shall be permitted in areas that are not designated as special flood hazard areas as defined
in Chapter 16.52, and are subject to the following regulations:
(a) Permitted Basement Area
Basements may not extend beyond the building footprint and basements are not allowed
below any portion of a structure that extends into required setbacks, except to the extent that
the main residence is permitted to extend into the rear yard setback by other provisions of this
code.
(b) Inclusion as Gross Floor Area
Basements shall not be included in the calculation of gross floor area, provided that:
(1) basement area is not deemed to be habitable space, such as crawlspace; or
Ch. 18.12-Page 15 (Supp. No 13 -10/1/2007)
18.12.100 Regulations for the Single Story Overlay (S) Combining District
(D) the cumulative length ofany excavated area or portion thereof that extends into a
required side or rear yard does not exceed 15 feet;
(E) the owner provides satisfactory evidence to the planning director prior to issuance of
a building permit that any features or portions of features that extend into a required
side or rear yard will not be harmful to any mature trees on the subject property or on
abutting properties;
(F) such features have either a drainage system that meets the requirements of the public
works department or are substantially sheltered from the rain by a roof overhang or
canopy of a permanent nature;
(G) any roof overhang or canopy installed pursua~t to subsection (F) is within and is
counted toward the site coverage requirements established in Section 18.12.040;
(H) such areas are architecturally compatible with the residence; and
(I) such areas are screened to off-site views by means oflandscaping and/or fencing as
determined appropriate by the planning director.
(Ord. 4869 § 14 (Exh. A [part]), 2005)
18.12.090 Basements
(2) basement area is deemed to be habitable space but the :finished level of the first floor
is no more than three feet above the grade around the perimeter of the building
foundation.
Basement space used as a second dwe~g unit or portion thereof shall be counted as floor
area for the purpose of calculating the maximum size of the unit (but may be excluded from
calculations of floor area for the total site). This provision is intended to assure that second
units are subordinate in size to the main dwelling and to preclude the development of duplex
zoning on the site.
( c) Lightwells, Stairwells, Below Grade Patios and other Excavated Features
(1) Lightwells, stairwells, and similar excavated features along the perimeter of the
basement shall not affect the measurement of grade for the purposes of determining
gross floor area, provided that the following criteria are met:
(A) such features are not located in the front of the building;
(B) such features shall not exceed 3 feet in width;
(C) the cumulative length ofall such features does not exceed 30% of the perimeter of the
basement;
(D) such features do not extend more than 3 feet into a required side yard nor more than 4
feet into a required rear yard, but where a side yard is less than 6 feet in width, the
features shall not encroach closer than 3 feet from the adjacent side property line;
(E) the cumulative length of any features or portions of features that extend into a
required side or rear yard does not exceed 15 feet in length;
(F) the owner provides satisfactory evidence to the planning division prior to issuance of
a building permit that any features or portions of features that extend into a required
side or rear yard will not be harmful to any mature trees on the subject property or on
abutting properties; and
(G) such features have either a drainage system that meets the requirements of the public
works department or are substantially sheltered from the rain by a roof overhang or
canopy of a permanent nature.
(2) Below-grade patios, sunken gardens, or similar excavated areas along the perimeter of
the basement that exceed the dimensions set forth in subsection (1), are permitted and
shall not affect the measurement of grade for the purposes of determining gross floor
area, provided that:
(A) such areas are not located in the front of the building;
(B) all such areas combined do not exceed 2% of the area of the lot or 200 square feet,
whichever is greater; that each such area does not exceed 200 square feet; and that
each such area is separated from another by a distance of at least 10 feet. Area
devoted to required stairway access shall not be included in the 200 square foot
limitation.
( C) such features do not extend more than 2 feet into a required side yard nor more than 4
feet into a required rear yard;
(Supp. No 13 -10/1/2007) Ch. 18.12-Page 16
ATTACHMENT H
May 8, 2008
Steve Broadbent
575 Washington Ave
Palo Alto, CA 94301-4046
steve.broadbent@hp.com
(650) 521-3958
Honorable Mayor Larry Klein and Council Members
City of Palo Alto
250 Hamilton Ave
Palo Alto, CA 94301
Via email
Re: Green Building Ordinance -Request to Prohibit Basement Construction
Honorable Mayor Klein and Council Members:
I urge City Council to strengthen City ordinances to prohibit the construction of
residential basements, especially basements which require dewatering during
construction.
The mechanical removal of millions of gallons of groundwater from a construction site
has detrimental environmental impacts, and it is disingenuous for a construction project
to be considered "green" when it builds a basement in an aquifer. One so called "green"
project in Old Palo Alto pulled an estimated 100,000 gallons of water per day from our
underground aquifer for a period of 6 months. The Green Building Ordinance under
consideration by the City Council does not adequately address this abhorrent practice,
and you should amend the ordinance to prohibit basement construction.
The Planning & Transportation Division Staff Report for the April 9, 2008, study session
on the proposed Green Building Criteria for Private Development recognized basement
construction as an issue needing further scrutiny, but staff has failed to pursue
satisfactory resolution:
"The Commission and the public asked several questions about basements,
including a) groundwater discharged, b) the effects of dewatering on groundwater
and potential toxic plumes, c) the amount of concrete used, and d) impact on
trees.
"The Public Works Department has, in the past few years, revised its basement
policy to prohibit dewatering basements after construction. Dewatering from
basements during construction is still allowed ...
Green Building Ordinance -Request to Prohibit Basement Construction Page 1of5
"During the Zoning Ordinance Update, staff commissioned EIP Associates to
study the impacts of extensive basement construction on groundwater ...
"Staff believes that the use of basements deserves continued scrutiny ... Planning
has included provision in the green building criteria that larger homes (including
basement floor area) must achieve a greater number of green point credits than
smaller homes to help compensate for these resource impacts. Other approaches
would require extensive discussion as to when or whether to continue to allow
basements ... In recent ordinance discussions, this issue was broached but not
pursued."
I agree with staff that the use of basements deserves continued scrutiny, but I am
disappointed that staff believes green point credits can mitigate the serious impacts
basement construction has on our city. Public Works has attempted to dismiss concerns
raised by many residents by declaring the impacts as "negligible" or by disavowing
specific knowledge. A response that "staff is not aware" should not be considered
closure on the issues raised.
I take exception to a number of the conclusions put forth by Public Works, and I ask that
Council direct staff to reconsider their findings, including but not limited to:
•
•
•
•
•
Impact to neighboring properties
Land subsidence
Impact on trees and landscaping
Waste of water
Other detrimental impacts
Impact to Neighboring Properties
Staff asserts "the study concluded that the impacts of basement construction were
negligible on the groundwater system and on the groundwater on neighboring sites."
However, the EIP study clearly stated that
"In the areas adjacent to the site being dewatered, the rate and flow directions of
the groundwater would be altered temporarily by the dewatering process.
Groundwater in the influenced area would move toward the base of the
excavation ... This effect could extend from several feet to several tens of feet
beyond the excavation."
My concern is not with the long term impact on the broader Santa Clara Valley
groundwater system. My issue is with the site-specific impacts on neighboring properties
and the local community. You should not allow macro responses to obscure the micro
view of real damage that residential basements cause.
There may be no discernable long-term effect on the broader surface aquifer beneath the
Santa Clara Plain (macro view), but the prolonged extraction of groundwater from 2164
Green Building Ordinance -Request to Prohibit Basement Construction
Webster Street most certainly sucked the groundwater from underneath neighboring
properties, including mine (micro view).
Although small compared to the volume of the surface aquifer (macro view), the volume
of space displaced by a basement could be several tens of thousands of cubic feet which
would displace groundwater flow around a newly constructed basement. This could be
significant locally (micro view), especially if there were other similarly sized basements
in the immediate vicinity (refer to EIP study, page 5). Several residents have horror
stories of how the utility basements in their established homes began flooding after the
construction of neighboring basements.
The Foundation Engineering Handbook, by Hsai-Yang Fang (1991), confirms that" ... the
process of dewatering can have side-effects that are harmful to the project under
construction, the other facilities nearby, or to the environment ... Improper dewatering ...
can cause damage to the structures being built or to adjacent structures."
Land Subsidence
It is well established that subsidence can occur with groundwater extraction, and the
effects of subsidence cannot be reversed where portions of the aquifer have been
compressed.
"Saltwater intrusion and subsidence in the Santa Clara Subbasin are documented
regional effects of the excessive removal of groundwater from the deep aquifer
over many years ... the SCVWD has been recharging the subbasin [with potable
water] thereby raising groundwater level ... and virtually eliminating further
overdraft-related subsidence. Such basin-wide effects could recur only if the deep
aquifer became overdrafted again. Because dewatering for basement construction
occurs only in the uppermost portion of the surface aquifer and involves only a
small amount of groundwater withdraw! [relative to the broader Santa Clara
Subbasin], no effects would occur in the deep aquifer." (macro view, refer to EIP
study, page 6)
Take that "macro view" and bring it up to the surface aquifer underlying my home. My
"micro view" is that the drawdown of the groundwater under adjacent properties can and
does cause localized subsidence depending on the soil properties in the area. After 7 5
years, my home shouldn't be "settling" any more, but cracks in the plaster and cracks in
the pavement developed during the extended dewatering at 2164 Webster.
Fang confirms that "ground settlement can occasionally be a problem. Lowering the
water table increases the effective stress in the soil. The stress increase is usually modest,
and most soils are not affected significantly. But if there are compressible soils in the
vicinity ... settlement may occur. Whether the settlement causes significant damage
depends on the thickness and consolidation characteristics of the compressible deposit,
the depth of drawdown and the duration of pumping, the foundations of the structures
within the zone affected, and the type of their construction."
Green Building Ordinance -Request to Prohibit Basement Construction Page 3of5
Impact on Trees and Landscaping
Not only do I disagree with the Planning Arborist's assertion that "the localized
drawdown of the water table during dewatering does not impact trees as their roots do not
typically extend to that depth," the EIP study contradicts that assertion:
"The possibility exists th'lt adjacent landscaping could experience deterioration
from reduced groundwater availability." (refer to EIP study, page 4)
Fang also confirms that, "trees ·or other plantings in urban parks may be affected [by
dewatering]." Regardless of ~hether tree roots extend into the aquifer or not, the strong
pull of drawdown wells during a dewatering operation accelerates the percolation of
surface waters and induces drought-like conditions as the soil dries out. Landscape
irrigation cannot and should not be considered sufficient mitigation of the drought-like
stress inflicted on trees during prolonged dewatering.
Waste of Water
The City has been studying the use of recycled water for landscape irrigation and other
non-potable uses, and a multimillion dollar recycled water project is being considered.
The City clearly recognizes the need for water conservation, yet it permits the intentional
discharge of millions of gallons of water into our storm drains. That simply doesn't make
sense.
Public Works has stated that the water pumped from the shallow aquifers typically goes
into the storm drain system and then into the creeks, some of which are "losing" creeks,
meaning they lose their water back to the shallow aquifers. Public Works asserts that the
water is pumped out of the aquifer and then added back to it. But Public Works fails to
acknowledge that there are no "losing" creeks in my neighborhood, only engineered
channels.
• Adobe is all concrete bottom and sides from Hwy 101 to Alma.
• Matadero is all concrete bottom and sides from Hwy 101 to Alma, except from
Greerto hwy 101
• Barron is all concrete bottom and sides from Hwy 101 to Alma except for about
800 feet just upstream of hwy 101.
Concrete channels are not "losing" creeks, and since the natural aquifer flow is from the
foothills to the bay, any recharge in the short sections near Hwy 101 does not repleni'Sh
the impacted neighborhood.
Green Building Ordinance -Request to Prohibit Basement Construction Page4 of5
Other Detrimental Impacts
In addition to the unnecessary waste of water, the large volume of water pumped into our
storm drains could rupture our aging storm drains, damage streets and underground
utilities, and cause a sinkhole to develop.
Fang also notes that groundwater in the vicinity of a dewatering operation may be
affected "by temporary reduction in the yield of supply wells, by salt water intrusion, or
by the expansion of contaminant plumes."
Call for Action
Mayor Klein and Council Members, I call upon you to take action to restrict residential
. basement construction and stop the destructive practice of de watering. Palo Alto wants
to be a leader in the Green Building movement. Please amend the Green Building
Ordinance to prohibit residential basement construction in Palo Alto.
Sincerely,
Steve Broadbent
Green Building Ordinance -Request to Prohibit Basement Construction Page 5 of 5
Attachment I
To: Palo Alto City Council & Planning & Transportation// Re: Dewatering and Basement Construction// Date: July 19, 2008
Honorable Council and Planning and Transportation Committee Members:
I am writing to express my concerns about dewatering and basement construction in Palo
Alto. I am a professional scientist who has specialized in groundwater hydrology since
1975. I have a BS in Geology from Dickinson College and MS and PhD degrees in
Hydrology from Stanford University. I have lived in Palo Alto for 31 years. The
following statements are my personal views as a resident.
I recently received a call from another Palo Alto resident who purchased an older home
near property that was being outfitted with a new house. Excavation for the new home's
basement required pumping over 18-million gallons of groundwater 35 feet to land
surface, where the water was discarded into the City's storm sewer. According to the
caller, this dewatering was carried out with the approval of the City, without the need for
a variance. The resident reported that dewatering volumes on the order of millions of
gallons have been produced in multiple instances in Palo Alto, as mega basements have
become popular.
I do not advocate a complete ban on basement construction. Nevertheless, it is clear that
large parts of the City are unsuitable for the sorts of basements being built. Projects that
require large-scale dewatering should not be allowed. The reasons are simple:
(1) Construction of finished (dry) space where any part of that space is below the water
table is not advisable and should rarely if ever be allowed. This is necessary not only to
protect the newly constructed space, but also to conserve energy and water resources and
to prevent overloading of the storm-sewer system. Building codes prohibit basements that
would be "subject to flooding." The maximum elevation of the water table during normal
rainy seasons, plus a reasonable safety margin, sets the limit for allowable subsurface
construction. The need for large-scale dewatering indicates that the structure being built
is subject to flooding by groundwater. It is not to anyone's advantage to build basements
in unsuitable locations. The City must uphold existing law.
(2) Extensive low-lying areas of Palo Alto have shallow water tables, rendering them
unsuitable for basements. These areas were prone to flooding prior to "reclamation"
projects that "channelized" the downstream reaches of creeks and diked off the Palo Alto
Baylands. Sea-level rise from global warming is underway. Sea-level rise will increase
water-table elevations in low-elevation areas of the City. Empirical projections based on
ICPP scenarios call for 0.5 to 1.4 meters (1.6 to 4.6 feet) of sea-level rise by 2100
( http://www.sciencemag .orgtcgitcontent1abstract131s1ss10/368). These projections are likely low
( http://www.sciencemag.org/cgi/co~tent/abstract/317/5841/1064).
(3) The cone-of-depression from construction dewatering involving extraction wells with
only a few feet of horizontal setback from adjoining properties will definitely extend
beneath the adjoining properties, with potentially harmful effects from desiccation and
differential settling. Palo Alto's soils are heavily textured "adobes" in which the dominant
minerals of the fine fraction are montmorillonitic (smectitic) clays. Smectitic clays swell
with wetting and shrink with drying. Although modem foundations are designed to avoid
1 of2
To: Palo Alto City Council & Planning & Transportation// Re: Dewatering and Basement Construction// Date: July 19, 2008
failure in soils that shrink and swell, older structures are vulnerable to harm. Dewatering
removes water from adjacent properties. It seems prudent to avoid situations where one
person's allow.ed dewatering can harm neighboring properties.
( 4) Wasteful consumption of City water resources is a serious issue. Eighteen million
gallons of water is about 24-thousand CCF (hundred cubic feet). If applied to a medium-
sized City park with 200,000 square feet of irrigated turf-roughly the size of the
Mitchell Park soccer fields-the depth of the applied water would be about 12 feet. This
represents one hundred weeks of irrigation-five years' worth at 20 irrigation weeks per
year. Virtually all water removed during construction ends up in the Bay via lined storm-
runoff conveyances. Virtually none of it recharges groundwater or soil moisture. Waste
on this scale is unconscionable.
( 5) The possibility of groundwater contaminants being captured by construction wells
poses risks at multiple locations throughout the City. As more commercial and industrial
areas are rezoned to residential uses, the number of risks increases. Many contaminant
plumes are mapped, but others are poorly characterized. Such risks additionally weigh
against construction dewatering.
In summary, basements must be restricted to areas that have adequately thick unsaturated
zones-not all areas of Palo Alto are suitable. Large-scale dewatering should not be
permitted. Preservation of property and avoidance of contaminant entrainment are
compelling reasons to reassess current practices. The public costs of construction
dewatering are unacceptably high. Groundwater is a City resource so precious that no one
should be permitted to squander it on grand scales.
Prudent restriction of dewatering and basement construction will protect all parties.
My only interest in this matter was a promise to a fellow Palo Altan-concerned by
groundwater impacts-to assess the situation and communicate my findings to you.
With best regards,
David A. Stonestrom
1000 S. California Ave.
Palo Alto, CA 94306
2 of2
ATTACHMENT J
Davldson%20Basement%20Excavatlon%20Photos.htm 9/15/08 5:55 PM
From: Williams, Curtis
Sent: Monday, September 15, 2008 5:55 PM
To: Williams, Curtis
Subject: FW: Basement Excavation Photos
from: Jodyldavidson@aol.com [mailto:Jodyldavidson@aol.com]
sent: Tuesday, April 22, 2008 6: 02 AM
To: Williams, Curtis
Cc: French, Amy
Subject: Basement Excavation Photos
Hi Curtis,
These are some photos to help explain what I meant when I was trying to explain that the underground footprint of
basements was too large.
On the smaller size lots, the builders often excavate closer to the allowed set backs.
Many often excavate right up to the lot line, and then the builders start putting in the concrete and rebar.
I have seen this many times.
People in adjacent homes have told me that they believe that the excavation has ruined the foundation of their homes.
Since the side yard is all concrete, there is no where for the water to flow, except laterally.
This causes flooding to neighboring homes. Additionally, there is simply not enough side yard to allow for planting, and the
rear set backs are really too small to allow for tree planting when the tree grows.
Basically, the homes on these lots are all home and no yard.
I hope that the city will consider reviewing their poli9ies on the allotted size of a new home on these smaller lots.
Allowing this building practice has caused a lot of disharmony within our community.
Many residents feared that their homes could actually fall into the adjacent excavation site, and in many cases they had to
pay for fencing to protect their property.
Many felt that the chain link fence was simply not enough protection when the builders excavate to the lot line.
Please remember that some of the adjacent older homes on the smaller lots may not have this 6 foot side allowance.
Regards,
Jody Davidson
file:// /S: {PLAN/ PLADIV /Cu rtis/Desktop%2 05.8.08 /Green /Basements/Davldson%20Basement%20Excavation%20Photos.htm Page 1of3
Green cement may set C02 fate in concrete
SFGale.mrn
Green cement may set C02 fate in concrete
Carrie Sturrock, Chronicle Staff Writer
Tuesday, September 2, 2008
(09-01) 19:18 PDT --Call him cement man.
~-__ -. _ r e
Attachment K
Back when Stanford Professor Brent Constantz was 27 he created a high-tech cement that
revolutionized bone fracture repair in hospitals worldwide. People who might have died from the
complications of breaking their hips lived. Fractured wrists became good as new.
Now, 22 years later, he wants to repair the world.
Constantz says he has invented a green cement that could eliminate the huge amounts of carbon
dioxide spewed into the atmosphere by the manufacturers of the everyday cement used in concrete
for buildings, roadways and bridges.
His vision of eliminating a large source of the world's greenhouse C0{-2} has gained traction with
both investors and environmentalists.
Already, venture capitalist Vinod Khosla is backing Constantz's company, the Calera Corp., which
has a pilot factory in Moss Landing (Monterey County) churning out cement in small batches.
And Carl Pope, executive director of the Sierra Club, says it could be "a game changer" if Constantz
can do it quickly, on a big scale and at a decent price.
"It changes the nature of the fight against global warming," said Pope, who has talked with
Constantz about his work.
That might sound like hyperbole, but the reality is that for every ton of ordinary cement, known as
Portland cement, a ton of air-polluting carbon dioxide is released during production. Worldwide,
2.5 billion tons of cement are manufactured each year, creating about 5 percent of the Earth's C0{-
2} emissions.
When Constantz learned about the high C0{-2} levels, he thought he could do better. After all, the
majority of his 60 patents have to do with medical cement.
He claims his new approach not only generates zero C0{-2} , but has an added benefit of reducing
the amount of C0{-2} power plants emit by sequestering it inside the cement.
http://www.sfgate.com/cgi-bin/article.cgi ?f=/c/a/2008/09/02/MNGD 129361.DTL&type=~ri... 9/4/2008
'\
Green cement may set C02 fate in concrete Page 2 of 5
To make traditional cement, limestone is heated to more than 1,000 degrees Celsius, which turns it
into lime -the principal ingredient in Portland cement -and C0{-2}, which is released into the air.
Constantz uses a different approach, the details of which remains secret pending publication of his
patent.
At his pilot factory, a former magnesium hydroxide facility that made metal for World War II
bombs, magnesium crunches underfoot as Constantz, wearing a pressed, blue button-down shirt
with rumpled shorts and sandals, outlines' how the process works.
He pointed to two enormous smokestacks billowing flue gases full of carbon dioxide next door at
Dynegy, one of the West's biggest.and cleanest power plants.
Constantz takes that exhaust gas and bubbles it through seawater pumped from across the
highway. The chemical process creates the key ingredient for his green cement and allows him to
sequester a half ton of carbon dioxide from the smokestacks in every ton of cement he makes.
Constantz believes his cement would tackle global warming on two fronts. It would eliminate the
need to heat limestone, which releases C0{-2}. And harmful emissions can be siphoned away from
power plants and locked into the cement.
The same process can also be used to make an alternative to aggregate -the sand and gravel -that
makes up concrete and asphalt, which would sequester even more carbon dioxide from power
plants.
"The beauty here is we're taking this old industrial polluti~g infrastructure and turning it into
something that will save the environment," Constantz said.
On a per-person basis, the United States is the world's worst C0{-2} polluter from all sources. But
according to the Netherlands Environmental Assessment Agency, China just surpassed the U.S. for
total carbon dioxide emissions.
China is expected to produce 47 percent of the world's 2.5 billion tons of cement this year,
Constantz said.
To power its new buildings and sustain its building boom, China constructs at least one coal-fired
power plant a week. Each one belches out enough C0{-2} to cancel the benefits of every hybrid on
U.S. roadways, said Constantz.
A C0{-2} molecule can travel from Beijing to San Francisco in less than a day through atmospheric
circulation, he said. So even with California mandating that C0{-2} emissions fall to 1990 levels by
2020, a crisis remains.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD129361.DTL&type=pri... 9/4/2008
Green cement may set C02 fate in concrete Page 3 of 5
"Carbon dioxide is a global problem, not a regional problem," he said.
As far as cost, Constantz estimates his cement would retail for $100 a ton versus roughly $no for
Portland.
The reason no one invented it before now, he said, is that pe~ple didn't truly understand the
dangers of C0{-2} until less than a decade ago.
Skeptics question product
He has skeptics.
Portland cement has a track record of more than 100 years, and any new material would have to get
incorporated into building codes, noted Rick Bohan, director of construction and manufacturing
technology for the Portland Cement Association in Skokie, Ill.
And Tom Pyle, a Caltrans engineer who serves on the cement subgroup of Gov. Arnold
Schwarzenegger's Climate Action Team, acknowledged that the technology is possible, but he still
wants to examine Constantz's cement.
"We hope they have a carbon-reducing viable construction material," he said. "They need to show
up with a bag of this so we can test it."
Constantz is confident he will prove himself. Initially, he proposes mixing his new invention with
Portland cement to ease a conservative industry into a new product. Concrete bigwigs have invited
him to speak about Calera cement at their annual World of Concrete in Las Vegas next February.
Power plant partnerships
Constantz envisions building cement factories next to power plants the world over. A team is
scouting out U.S. locations. While Dynegy has supplied Constantz with some flue gas, it hasn't
entered into a formal agreement.
"As we're looking into the future, we're very interested in technology that would help capture C0{-
2} from the flue gase~ and turn it into a product that offers a benefit," said Dynegy spokesman
David Byford.
It could be good for business. California has mandated emissions reductions. And Congress is
working on legislation that would allow high polluters to buy credits from those with low
emissions. Power plants would have a huge incentive to sequester their C0{-2} in cement.
But even if Constantz succeeds, the world would still need to do much more to fight C0{-2}
emissions, said Chris Field, director of the department of global ecology at the Carnegie Institution
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD129361.DTL&type=pri... 9/4/2008
Green cement may set C02 fate in concrete Page 4 of 5
for Science at Stanford. "It's a big, long complicated game," he said. "As we develop each new
segment of the solution we need to embrace it and deploy it and work hard to develop the next
segment of the solution."
Coral basis of idea
Big ideas can form in haphazard ways. The one for bone cement began during a televised football
game, when Constantz read an osteoporosis article in the New England Journal of Medicine. Three
weeks later, as he studied a coral reef, it occurred to him he could maybe synthesize coral skeletons
in human bones.
His new cement mimics how coral reefs form, too. Coral uses the magnesium and calcium present
in seawater to create carbonates much as he's using C0{-2} and seawater to make carbonate.
This latest invention took 18 months to conceive and execute. He feels it's one of the most
important things he's ever done.
"Climate change is the largest challenge of our generation," he said.
Who is brent constantz?
Profession: An associate consulting professor in Stanford's department of geological and
environmental sciences and founder of the Calera Corp. Created and sold three other companies -
Norian Corp., Corazon Technologies Inc. and Skeletal Kinetics.
Education: UC Santa Barbara, bachelor's of science (1981); UC Santa Cruz, doctorate (1986)
Family: Married and father of four.
Pastime: Surfing and rock climbing.
Concrete facts about cement
2.5 billion tons of hydraulic cement is produced worldwide annually. Add sand and gravel and
that makes more than 9,000 million cubic yards of concrete. That's more than enough concrete
to pave an eight-lane highway from the Earth to the moon and back again -twice.
If you stayed on the planet, that same eight-lane highway would circle the Earth almost 40 times.
Source: Portland Cement Association
E-mail Carrie Sturrock at csturrock@sfchronicle.com.
http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD12936I.DTL
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD129361.DTL&type=pri... 9/4/2008
New Aquifer Filling Station
Revised 5/26/2015
1
Attachment B
Piping System
•Arrange piping system to draw water from settling tank being careful to keep the inlet a minimum of 1-2 feet above the
bottom of the tank to avoid settlement residue.
2
Locate the Filling Station
•Filling station should be located at the property line outside of the construction fence.
•Try to locate the station in a place where parked vehicles will not prevent equipment from using it, i.e. on a corner, near at
the edge of a driveway, etc.
•The filling station should be accessible 24/7.
3
Filling System
•Piping runs from the settling tank to a pump capable of providing a minimum of 150-200 gpm.
•Outlet of pump runs to lockable box where a standpipe is constructed.
•Standpipe contains a valve and outlet fitted with a MALE 2 ½” NH threaded fitting (Fire Hydrant threads).
•Inside the box is also located a switched GFI outlet to which the pump is plugged into. When the switch is thrown, the
pump turns on. This switched outlet is connected to the construction site’s temporary power. The GFI power outlet may be
placed somewhere outside the box, however, the switch should be inside. An “in-use” cover must cover the switch/outlet.
•A hose with a male connection shall be stored in the box to allow the water to be used for dust control onsite and for filling
tanks without pre-attached hoses or fittings.
•A standard hose bibb shall be installed next to the box to allow for gravity-fed filling of smaller “neighbor containers”.
4
Plumbing Signage
•The piping outside of the property lines needs to comply with California Plumbing Code Section 603.5.11:
•Each outlet on the non-potable waterline shall have posted: “CAUTION: NONPOTABLE WATER, DO NOT DRINK.” This would
apply to the hose bibb utilized by neighbors for non-potable purposes. The CPC also requires that exposed portions of the
piping be properly identified to the satisfaction of the AHJ. CPC Section 601.2 provides identification for non-potable
systems within a building. Although the proposed work is not within a building, the method would adequately identify the
piping system.
•Section 601.2 Non-Potable Water System Identification
•The system shall have a yellow background and black uppercase letters, with the words “CAUTION: NONPOTABLE WATER,
DO NOT DRINK.” The required piping identification shall be every 20 feet. The sizing of this lettering should be per CPC Table
601.2.2.
•This ‘signage’ comes in the form of stickers and can be easily found online.
5
Fill Point and Discharge Signage
•The contractor shall provide a sign according to Public Works specifications and attach it to the outside of the fill station box.
•The contractor shall also provide signs to be mounted on a standard “A-frame” barricade to be placed at the dewatering
discharge point (usually a catch basin).
•Upon completion of dewatering activities, the signs shall be returned to the Public Works Inspector for recycling.
6
Water Station
Sign Specifications
•These specifications are provided as guidance to produce/order consistent signs:
•This sign is aluminum, 20.5” tall by 14” wide. The margin is 0.25” and the border is also 0.25” wide.
•“Water Filling Station” is 1.5” tall, Highway Series E font.
•“Suitable For Irrigation Purposes” is 0.75” tall, Highway Series B font.
•“Do Not Drink” is 1.2” tall, (font as it is part of the symbol). The red circle and slash has a circumference of
4.5”.
•The city logo is 4.2” tall by 2.2” wide.
•Mount this sign to the water station door.
7
Discharge Point
Sign Specifications
•These specifications are provided as guidance to produce/order consistent signs:
•This sign is aluminum, 24” tall by 24” wide. The margin is 0.375” and the border is 0.625” thick.
•“Non-Potable Water Discharge” is 2”tall, Highway Series C font.
•“Do Not Drink” is 1.2” tall, (font as it is part of the symbol). The red circle and slash has a circumference of
4.5”.
•“To Use This Water…” is 1” tall, Highway Series C font.
•The city logo is 4.2” tall by 2.2” wide.
•Mount this sign to each side of an A-frame barricade (2 signs total) and place it at the discharge point.
8
Log Sheets
•Copies of the following log sheets with a pen
shall be attached to the inside of the door of
the filling station.
•All users of the water filling station shall fill
out the form for each use.
9
Log Sheet: Available from Public Works
10
Instructions
•Attach a copy of operating instructions to the
inside of the box.
•Sample instructions:
11
Security
•Box should be sturdy and locked with a
combination lock.
•Provide the lock combination to Public Works
– Engineering Services.
12
Inspection
•NO DISCHARGE IS ALLOWED WITHOUT A DEWATERING PERMIT.
•Once there is groundwater in the settling tank, contact the Environmental
Compliance division at (650) 329-2122 or (650) 329-2430 to have the water tested.
•Public Works will contact you to inform you of the results.
•Once the station is constructed and ready to operate, contact Public Works
Inspection at (650) 496-6929 to schedule an inspection.
•Once the Inspector has approved of the station installation, Public Works -
Engineering Services can issue you the dewatering permit.
13
Important Notification
•Contractor shall notify Public Works –
Engineering Services ONE WEEK prior to
ending dewatering operations.
•This will allow City staff to adjust vehicle
operations and routes accordingly.
14
Final Notes
•The New Aquifer Filling Station is a quickly evolving program -
changes, modifications, revisions, and additional conditions,
policies, and equipment required may occur at any time.
•This handout is a living document and will be revised as the
program develops.
15
Questions?
•Contact:
Mike Nafziger, P.E.
Senior Engineer
Public Works – Engineering Services
(650) 617-3103
mike.nafziger@cityofpaloalto.org
Or,
Public Works – Engineering Services
(650) 329-2152
16
GROUNDWATER
PUMPING
HAPPENING
IN YOUR
NEIGHBORHOOD
A BASEMENT CONSTRUCTION PROJECT
in your neighborhood is pumping water
to a stormdrain which leads to a creek.
This groundwater cannot be used as
drinking water, but it can be pumped to
creeks or used for irrigation and dust
control. Creeks would ultimately receive
this same water if it was not pumped
there first. This water is important to the
creek and Bay ecosystems.
The construction project in your
neighborhood offers a residential filling
station to access some of this pumped
water for use on landscaping.
Visit cityofpaloalto.org/recycledwater or
call (650) 329-2151, Press option #8
for filling station locations and additional
information.
Attachment C
Updated and posted 8/11/15
Groundwater Pumping From Building Sites
Frequently Asked Questions
During this time of severe drought, our community is working hard to conserve
water. So when community members observe water pumping from construction
sites, they want to know what is happening. Here are answers and information to
help address the most frequently asked questions we have heard.
Q. What is the water that I see running into the storm drain from construction
sites?
A: During the construction of a basement or underground garage there is
sometimes a shallow upper groundwater aquifer that must be temporarily
pumped down to allow construction to move forward. This groundwater is not
the same water that would be used for drinking.
Q: Does the City regulate the pumping and discharge of this water?
A: The City permits the discharge of this water to either the storm drain or the
sanitary sewer, depending on the water quality. The water is sampled and tested
for cloudiness, salinity and acidity. Only very clear, high quality water can go to
the storm drain. Temporarily pumping this water is standard practice in areas
with groundwater closer to the surface to allow construction to proceed, and no
practical alternative has been found. Using the water for irrigation and dust
control is possible, and the owners and construction managers are strongly
encouraged to find uses for the water.
Q: Given the high quality of the water and the severity of the drought, why
does the City allow it to be “wasted” by discharging it into the storm drain
system?
A: The shallow water aquifer being pumped contributes to the flow of our creeks
and to the Bay. The groundwater is part of the water cycle for the Bay and
enhances the habitat and improves the quality of the creeks and lower South San
Attachment D
Updated and posted 8/11/15
Francisco Bay. When the shallow aquifer is pumped from basement construction
sites into storm drains, it travels a different path, but ends up in the same place:
the lower South Bay. So, the water is not wasted, but rather is used to improve
the Bay’s habitat and ecosystem, whichever pathway it takes.
Q: Can’t this water be used for other purposes?
A: The pumped water hasn’t been disinfected or sufficiently tested to drink or use
inside the home. Palo Alto‘s emergency drinking water wells tap into a much
lower and more protected aquifer. However, the pumped water could be used
for irrigation, dust control or similar uses. Palo Alto now requires that contractors
have the pumping system fitted with valves and connections so that City crews
and others can fill water trucks, street sweepers and other containers. For truck
fill stations, the water is tested for acidity and salinity. Private parties can also fill
trucks and containers. Such “fill-stations” are now in place at the Palo Alto active
basement construction pumping sites listed below:
1405 Harker
1820 Bret Harte
804 Fielding
713 Southampton
3832 Grove
2230 Louis
View our map of FREE Water Filling Stations.
The site owners and construction managers are encouraged to find more water
users, but this will continue to be a small fraction of the total pumped water.
Call 650-617-3103 for more information about accessing the fill stations.
The volume of water being pumped is large compared to pump truck capacities,
but is too small and too shallow to impact the very deep and very large Palo Alto
emergency ground water aquifer.
Updated and posted 8/11/15
Q. What happens after construction?
A: In recent years, Palo Alto has required that structures be built as water tight so
that groundwater flows around a building, rather than into it. But a number of
older buildings leak, and water is pumped out of the building basement/garage
into the storm drain or sanitary sewer. Palo Alto City Hall and 525 University are
two of the largest “dischargers”. We have looked at utilizing the water from City
Hall, but it has not proven to be cost effective. With new water restrictions in
place, this issue is being reexamined once again. However, the City Hall water
does go through the storm drain to San Francisquito Creek where it supports
habitat, including for fish, especially in the summer when there is no rainfall.
Q. What can I do if I see water being wasted?
A: The City has hired a part-time Water Waste Coordinator who is specifically
dedicated to drought response actions. Need to report a leak, runoff or waste?
We have many communications means for you! Please let us know!
Report water use incidents through the City’s PaloAlto311 web or mobile
app at cityofpaloalto.org/services/paloalto311/ or go visit to
www.cityofpaloalto.org/water to access the link directly.
Contact the City’s Water Waste Coordinator at 650-496-6968 or
Martin.Ricci@CityofPaloAlto.org - or -
Call Customer Service at (650) 329-2161 - or –
Email UtilitiesCommunications@CityofPaloAlto.org - or –
Call Utilities Emergency Dispatch at (650) 329-2579
1 10/5/2015
GROUNDWATER PUMPING FOR RESIDENTIAL BASEMENT CONSTRUCTION
Frequently Asked Questions
Save Palo Alto’s Groundwater, a Community Resource
Is groundwater pumped for residential basement construction?
Yes. Very large amounts of groundwater from the shallow surface aquifer are pumped to build
basements when below ground soils are saturated to provide dry soils using a commercial-scale
construction process termed “dewatering.” This technique is now being permitted for
constructing residential basements in Palo Alto at a rapidly increasing rate, from an average of
five (5) per year (2006 – 2008) to at least 14 this year. Dewatering is used only at those sites
with water saturated soils; it is not used at drier sites.
Why should I care about groundwater pumping for basement construction?
Aquifers and groundwater are a community and public trust resource that, although unseen,
play an important role literally supporting structures and infrastructure, draining storm water,
and storing and providing moisture for our canopy and plants.
What are the effects of removing groundwater?
Removing groundwater has a variety of impacts. The forces exerted by groundwater literally
support the ground, structures and infrastructure and through capillary action, provide water to
our trees.
The shallow surface aquifer pressure increases the recharge of the deeper aquifer which is used
for irrigation and on which Palo Alto relies for emergency water.
Lowering the water table locally causes ground settling. This settling may not be uniform across
structures, which may then develop either tight doors or windows, or permanent cracks in
foundations, walls or masonry. Settling of even less than an inch is adequate to cause
permanent structural damage. Lowering the water table below the seasonal normal fluctuation
can cause irreversible compression of the soil (hysteretic soil compaction).
What are the effects of lowering the water table on vegetation?
Water available for trees and plants is reduced. Soils wick water up, much like sponges,
resulting in increased soil moisture several feet above the water table, well into the root zones
of trees in much of the area in which dewatering is occurring.
What are the impacts of these basements after construction?
Both the City of Palo Alto and the Santa Clara Valley Water District provide incentives to install
permeable pavement to reduce the amount of storm water entering storm drains and instead
soak into the ground, thereby reducing flood risks and recharging aquifers.
Basements displace soils that would otherwise be available to absorb rain water, increasing the
probability that rain water will flow into the storm drains.
Attachment E: Correspondence
2 10/5/2015
Much of Palo Alto is known to have covered gravel beds from former creekbeds. Basements
are dams in the unseen rivers that flows through the soils, gravel beds and aquifer beneath Palo
Alto. Water needs to flow around these basements. If water cannot flow through the soil fast
enough, it will flow above the soil, into the storm drain system, and if the storm drain capacity
is exceeded, will flood our streets and properties.
The water table/water pressure surrounding a basement is locally higher, in the same manner
as water in a flowing river is higher as it flows around an obstacle. The locally higher water
table increases the risk that basements in neighboring properties will flood.
What can I do if my property is damaged by ground settling caused by groundwater
pumping?
You’re on your own. You must resolve any damage claims directly with the party that caused
the damage. The City will neither order the dewatering to stop nor help you with any damage
claims. You may sue. In that case it will be necessary for you to prove that the specific
dewatering operation was the cause of the damages, and most likely pay attorney’s fees, which
might be reimbursed if you obtain a judgement in your favor.
How much water is pumped?
In total, it is estimated that 126 million gallons (16,000,000 ft3) of groundwater has or will be
pumped out for the construction of 14 basements in Palo Alto in 2015 alone. This is enough to
cover a football field 275 feet deep, or fill 50,400 water tank (2,500 gallon) trucks, or provide
enough water for 18,000 average Palo Alto residences for the entire month of July, 2015
(equivalent to 40-50% of the state-mandated water conservation goal for all single family
residences in Palo Alto for a year) or lower the aquifer by more than 1 foot over an area of 1
square mile.
This estimate is based upon the midpoint of City’s estimate of 8 – 10 million gallons (1.2 million
cubic feet) per basement. For some basements, more than 20 million gallons is pumped. The
amount of water being pumped out is not metered.
Where is groundwater pumping occurring?
Most of the residential dewatering projects are concentrated in an area of approximately 1
square mile bounded by Webster Street, Louis Road, Colorado Avenue and Channing Avenue,
although two are near Middlefield Road further south.
From where is the water pumped?
Groundwater is typically pumped from 15 to 25 feet below grade, and the groundwater table
locally lowered about 2 feet below the bottom of the basement in the area to be excavated.
The “bottom” of the basement is generally 10 – 20 feet below grade; some are below sea level.
Groundwater is typically pumped at a rate of 50 – 100 gallons per minute continuously for 3 – 6
months.
3 10/5/2015
How much do government agencies collect in fees and permits for construction dewatering?
The City of Palo charges approximately $710 for a dewatering permit for 6 months.
There is no usage-based fee or assessment for discharging the groundwater pumped out for
construction into the storm drain. The total cost to the developer for removing this resource
from our aquifer is about $710.
How much do residents pay for equivalent water disposal in the storm drain?
The Storm Drain Fee for 1 equivalent residential unit (ERU) is $12.63 / month ($151.56 / year).
A single dewatering site will dump as much water down the storm drains as the city estimates
would go into the storm drains from 480 residences (1 ERU / residence) in a year. Developers
are not currently required to pay any additional fees to compensate for the heavy use of the
city’s storm drains, even though a “fair share” payment would be $72,748 for a typical
basement.
How much would Santa Clara Valley Water District charge for a resident to pump non-potable
groundwater for irrigation?
Santa Clara Valley Water District charges about $600 / acre-foot (43,560 ft3) for a permit to
pump groundwater. For the amount of water pumped for a typical basement, the cost would
be approximately $16,500. However, a specific exemption from fees is provided for
construction dewatering in the shallow aquifer. The fee to builders is zero.
Is this groundwater pumping sustainable?
The amount of water removed from the aquifer in 2015 is roughly the same as would be
available to recharge the aquifer from average (not drought) rainfall for one year, after allowing
for runoff and evaporation over an area of 1 square mile.
What happens to the pumped groundwater?
Approximately 99% is dumped into the storm drains, which then flows to the Bay.
Isn’t this pumped water available for irrigation for free?
The City requires faucets with hose connections and fill stations for water tank trunks at each
dewatering site. There are no requirements for the actual use of the water or the pressure
supplied to hose connections for neighborhood use; City policy effectively condones wasting
water. In practice, the water is not substantially used. Although the water is of high quality
and usable, it is wasted.
How and when is the shallow surface groundwater replenished?
Primarily from rain and landscape irrigation. Precise recharge rates are not known, but it is
believed to be in the range of months to years.
Doesn’t the water flow to the Bay anyway, and therefore doesn’t pumping the groundwater
improve the environment of the Bay?
The aquifer and soils have an important role in transporting storm water to the Bay; more
water flows in the unseen river beneath our homes to the Bay over the course of a year than
4 10/5/2015
down the creeks. However, during the summer, there is little flow in the aquifer (there almost
no flow in creeks either). Dewatering locally lowers the water table below its normal historical
low level, and in some cases below sea level, much as pumping water from a lake could lower
the lake level below the outlet level.
Hasn’t the City already carefully studied dewatering?
The City commissioned a study in 2004, and City staff reviewed the study in 2008 after receiving
citizen complaints. Not only are several important issues not addressed, especially related to
local effects, there are important differences between the current situation and the time of the
original study. Existing City dewatering policy does not anticipate the current number or water
volume of dewatering activities within the City. Despite acknowledgment by the study that
there will be “temporary and local effects,” the study does not meaningfully address localized
impacts, including ground settling, reduced soil moisture for trees, flood risks and storm water
management, public compensation for the use of the water, or public policy in an era of climate
change. Furthermore, it is incorrectly assumed that short-term effects will not cause
permanent damage.
From where did this information come?
All information in this document is either provided by or derived from the City of Palo Alto, the
Santa Clara Valley Water District, USGS topographical maps, the US National Oceanographic
and Atmospheric Administration, and materials provided by degreed professionals in soil
sciences or hydrology, including documents in the Public Record for the City of Palo Alto.
What is the objective of Save Palo Alto’s Groundwater?
Palo Alto’s groundwater is a community resource too valuable to freely pump and dump down
storm drains simply for the construction of residential basements. We are requesting that the
City of Palo Alto enact an immediate moratorium on new permits for the pumping out of our
groundwater (“dewatering”) for the construction of residential basements in Palo Alto to
further study the effects of dewatering. Dewatering should only be permitted if the study
shows negligible impacts, including effects on storm water management and flood risks, and
policy is updated to require minimization and complete mitigation of all impacts including
requiring full use of the pumped water, payment for use of infrastructure and resources,
protection of infrastructures, properties, and the canopy, with all costs to be assumed by the
developing party.
Is a more detailed document available?
Yes, a White Paper including references is available upon request.
How do I obtain further information or help with this effort?
Send an e-mail with your name and contact information to
PAgroundwater@luxsci.net
Questions related to the City of Palo Alto policies on permitting the
pumping of groundwater for the construction of residential
basements
Keith Bennett
8/11/2015
Background: My concerns relate to the documented local and transient impacts of new basements and
their construction, as well as the permanent impacts of new, large basements on the capability of local
soils to handle rainwater during periods of heavy rain, such as has been experienced in 1982 and 1998.
My primary concern is not the apparent “waste” of a groundwater resource during a drought (although
the amount of water pumped for basement construction is about 10% of the total 24% conservation
goal for the City, and report indicates that the surface aquifer being pumped has partly been
replenished by imported water from the Delta). Aside from considerations of water quality, I am aware
that City has far more water that could be used for irrigation (aside from delivery cost) available from
the Water Treatment Plan
I have read the 2004 report by EIP, as well as the Staff Report from Curtis Williams dated 9/24/2008.
From my reading of these reports, they do not support the conclusions that dewatering on the current
scale in Palo Alto is not without significant adverse effects.
1. My understanding is that the two documents listed above, plus soils reports generated from the
construction of new buildings, especially buildings with basements are the primary bases for City
Policies. The City has prepared a map showing groundwater depth based upon measurements
related to construction. This map is available in electronic format. The soils reports from new
construction are copyrighted, and may be viewed, but may not be copied. I assume, however,
that the City could, if desired, use the information in the soils reports for analysis and modelling
purposes.
Is my understanding correct and substantially complete?
2. Importance of recharge rates and source on the overall impacts of dewatering on the shallow
aquifer. Long term impacts are only negligible if they aren’t offset by recharge.
The 2004 Report primarily focuses on the impact on the level of the entire Santa Clara Subbasin
surface aquifer, and simply assumes that the water pumped in a year will recharge the next year.
Shouldn't the basis for policy consider not only the fraction of the total available aquifer
pumped, but also critically consider recharge?
The report states the following:
a. There are 5 – 10 basements / year constructed with dewatering in Palo Alto, and as the
aquifer extends beyond Palo Alto, and other cities may also pump groundwater, the
total impacts on the aquifer would be far more significant. It would appear that
annually >1% of the aquifer / year or 10% per decade could be depleted. This is not
insignificant. To avoid long-term effects, the groundwater must be recharged.
b. The subsurface aquifer has been significantly recharged by IMPORTED (i.e. purchased)
water (Pg 6, see above):
“It is known, however, that the importation of potable water and the SCVWD controlled
recharge program have assisted groundwater levels in the subbasin to rise 200 feet in
the last 40 years. Most of the rise has been in the surface aquifer.”
Note: it is the surface aquifer that is being depleted for dewatering.
A January, 2015 document from the SCVWD “Where does our water come from?”
(attached) lists three primary sources for groundwater replenishment: “3. Water
importation from the Delta, which the district also releases to creeks and recharge
ponds for managed groundwater recharge.”
Should Palo Alto have a policy that accelerates sending of water to the Bay through
groundwater pumping in a drought when replacement supplies are restricted, and
furthermore, it appears from public documents that some of the water being pumped
for basement construction may, in fact, may in fact be due to SCVWD groundwater
recharge programs?
Is it reasonable that those dewatering be permitted to use this resource without
compensation based upon consumption, i.e. shouldn’t the dewatering amount be
metered and charged for example to pay SCVWD for replacement water?
3. Local Effects
The EIP report does not provide any basis to support the statement (Pg. 5) regarding the
geographical extent of local lowering of the groundwater, and provides no information on the
volume profile of the dewatering:
a. Assuming a dewatering of 1,000,000 ft3, well below the 7,000,000 ft3 mentioned as
typical in the report, but comparable to the lower end of the pumping rates and
durations mentioned in the City Staff report corresponds to a volume of 500 x 500 x 8
feet, assuming 50% porosity of the soil. It is clear that some effects must extend well
beyond “several tens of feet.” It is also clear that the extent of dewatering must depend
upon local soil composition, the depth of pumping and the time (and rate) that the
water is removed.
b. The 2004 states “local settlement on the order of fractions of an inch could occur.” (pg
7.) Settlement (either temporary or permanent) of even fractions of an inch is adequate
to break windows, cause cracks in masonry and plaster, or require doors to be reworked
to open and close properly. There is no guarantee that settling will be perfectly level
across a nearby property, which is likely the case if a gradient is created in the soil
moisture content. Furthermore, the dewatering may extend below the depth of
normal “seasonal” water table variation and therefore may affect the supporting
capacity of soils between the dewatering depth and the normal “low level” of seasonal
water table fluctuation.
Reports by homeowners (including the letter in the 2008 Staff Report from the resident
at 575 Washington), myself of home damage and a broken water main on N. California
several hundred away from, but particularly correlated in time with dewatering events.
Could these events provide evidence that dewatering is, in fact, causing at least
temporary settlement large enough to affect infrastructure and homes, and that the
extent may be further than assumed?
c. There is no discussion on the impacts of dewatering on soil moisture (used by plants)
above the aquifer. The Santa Clara County Water District leaflet compares soils to a
sponge:
The relevant question is the extent to which dewatering reduces soil moisture in the
surrounding area not whether or not tree or plant roots are below the water level of
the aquifer (generally, plants desire moist, but not saturated soils, as they need air,
therefore the roots of land plants are generally not in saturated soils. Like sponges, soils
wick water upwards from the aquifer. Is soil moisture unchanged above the aquifer
when the water table is locally and temporarily lowered? It is important to consider
the effects of dewatering in the spring, when soil moisture and the water table are both
higher. Isn’t reducing soil moisture earlier in the year in the root zone of plants is more
or less equivalent to an artificial drought?
Of course, it is possible to compensate for lower soil moisture by watering plants more,
however this is quite expensive during conditions such as the current drought, and
furthermore the expense is borne by the affected homeowners and city plants (e.g.
trees). If dewatering does increase the need for supplemental watering, then, isn’t
dewatering in practice indirectly increasing demand for potable water (as it’s 1/10th the
price of recycled water).
4. Long term impacts of basements on flooding risks during storms
A simple analysis shows that basements extending into a zone of saturated soil (once
constructed) will significantly and negatively affect the ability of local soils to hold and drain
rainwater during heavy storms, with increased risks of flooding, either in neighboring homes
and in wider areas.
a. The construction of basement means that there is no soil in the removed volume to
absorb rainwater. As basement and lightwell can cover 35% of the lot, and any
basement that requires dewatering for construction by definition extends to saturated
soils, the local reduction in the capacity of soils to hold rainwater is significant. The
result is a locally higher water table / water pressure, at least temporarily until the
water can drain. The locally higher water table increases the risk that neighboring
properties, especially those with older basements will flood.
The 2008 letter from the resident of 575 Washington mentioned the same concern.
Complications of basement flooding can be significant. In 1998, basement flooding
triggered a fire at 595 N. California (a pilot light was extinguished by the water; the
escaped gas then exploded when lit by a different pilot light). Additionally many
basements of older homes were flooded. Basements only rarely flood.
During the 1998 storm, the saturated water line along Webster St. near N. California
was about 3- 4’ below street grade, indicating that there is no significant extra capacity
in the soils, at least in some parts of the city. It is likely that soils were saturated closer
to the surface in lower areas.
If the soils become saturated to the surface, rainwater will no longer be absorbed and
instead will flow into the storm drains. If the storm drains cannot handle the additional
water, localized street flooding will occur.
The City provides rebates for the use of permeable paving materials to reduce the load
on the storm drains. This assumes that the soils can absorb the water and release it
more slowly.
Is the construction of large (and deep) basements in areas that have risk of soil
saturation above the basement level consistent with this policy?
Is a policy that increases the risk of flooding wise? Is it appropriate for Green Building
Certifications?
b. Basements are like dams in the unseen river through the soils (and aquifer) beneath
Palo Alto, and impede the discharge of water during periods of heavy rain, increasing
the level of saturated soils, and the risks of flooding. We would not think of blocking
any creek, yet basements are doing so for the channel that carries the most water to the
Bay.
i. The soils and aquifer under Palo Alto surely carry significantly more water to the
Bay than San Francisquito Creek over the course of a year. This can be easily be
shown by calculating the volume of water in even 12” of annual rainfall that falls
on the area (about 3.3 x 1.8 miles) of Palo Alto between El Camino and San
Francisco Bay and comparing the annual volume of water to that which flows in
San Francisquito Creek. In addition, the soils and aquifer must carry water from
lands west of El Camino, including Stanford and the foothills.
ii. The potential of basements to block aquifer / soil water flows is very significant.
Basements are now quite large (perhaps covering ½ of the property width) and
a very large fraction of new construction (~70% in permitted areas) includes
finished basements.
Have the impacts of basements on the capacity of our soils to handle
rainwater during heavy storms been properly considered?
From: Leah Rogers [mailto:leah.rogers@stanfordalumni.org]
Sent: Monday, October 26, 2015 6:38 PM To: Council, City; Keith Bennett Subject: re: Per request of Greg Schmid during Oral Comments at the Oct 5 2015 City Council Meeting Dear All:
Below is my effort to put in writing what I said in the Oral Comments period of the October 5
2015 City Council Meeting. I have also included some references at the request of Greg Schmid. Thanks you for your time and listening to these thoughts about the dewatering issue. Sincerely, Dr. Leah Rogers
(Ph.D. from Stanford in Hydrogeology)
The 2004 EIP report suggests the range of influence on the
water table aquifer is on the order of tens of feet from the
dewatering well. The amount of water table drawdown
necessary in construction of basements in Palo Alto is
approximately 15 feet (i.e. drawing down the water table from
10 ft below ground surface to 25 ft below ground surface. If we
consider standard calculations of radial flow applications of
Darcy’s Law (Freeze and Cherry, 1979 (note Eq 8:12-8:15);
Manning, 1997; Bennett et al., 1990), a lowering of the water
table level approximately 15 feet an unconfined aquifer in
alluvial deposits may create a cone of depression that spreads
out towards a few hundred feet in any direction. This assumes
some general hydraulic conductivities and other aquifer
parameters that could be in alluvial deposits in this area. Note
regional studies suggest hydraulic conductivity values may
range between 260 and 6000 gpd/ft2 (McCloskey and
Finnemore, 1996). There are many major factors that influence
the drawdown of the water table: thickness of the water table
aquifer, interfingering of layers that may inhibit flow (aquitards
in which case coefficients would have to be assumed to account
for leaky aquifers), and whether or not steady-state is reached.
Precise predictive modeling would require to collection of data
from time dependent well testing. However, we may say
qualitatively where there were more sands and gravels the cone
of depression would reach further than if there were tighter silts
and clays.
When several of these projects going on in the same
neighborhood, which is the case in Palo Alto, cones of
depression may interact cumulatively. As the dewatering effect
from multiple projects are cumulative and interact with reduced
irrigation, it is difficult to assign “responsibility” for damages to
property or landscaping to specific dewatering projects.
The drying out of soils is often not perfectly reversible. This is
called hysteretic soil compaction. For example, wet clay worked
into a dry piece of pottery cannot simply be put back into it’s
original state by submerging it in water. Imagine over a 3-4
month dewatering project that particularly the interfingering
clays in the subsurface will cause unequal rewetting. It is quite
plausible that the scale of these dewatering projects are
responsible for the additional cracks in walls and foundations
which neighbors in the area have noted. For example, the 2008
City Manager’s Report includes a letter from Steve Broadbent
raising such issues.
Overall, it would seem that the City of Palo Alto would do well
to require dewatering projects to provide specific
characterization and predictions of groundwater impact during
the course of the proposed project before approving any
dewatering especially in times of drought and water-
conservation. Even better would be adoption of construction
practices and project designs that significantly reduce the need
for dewatering, especially considering reduced irrigation in the
area during droughts.
References:
Bennett, Gordon D., Thomas E. Reilly, and Mary C. Hill. 1990.
Technical Training Notes in Ground-Water Hydrology; Radial
Flow to a Well. US. Geological Survey Water Resources
Investigations Report 89 4134.
http://pubs.usgs.gov/wri/1989/4134/report.pdf.
Freeze, R.A. and J. A Cherry. 1979. Groundwater. Prentice Hall
Inc., Englewood Cliffs, NJ. 604 pp.
Manning, J.C. 1997. Applied Principles of Hydrology. Prentice
Hall, third edition, 276p.
McCloskey, T.F. and E. J. Finnemore. 1996. Estimating
Hydraulic Conductivities in an Alluvial Basin from Sediment
Facies Models. Ground Water, Vol. 34, No. 6 November-
December 1996. http://info.ngwa.org/gwol/pdf/962962189.PDF.
On Wed, Jul 15, 2015 at 4:18 PM, Bobel, Phil <Phil.Bobel@cityofpaloalto.org> wrote:
Ms. Relman:
Our Assistant City Manager, Ed Shikada has asked me to respond to your 7/14 email about the
pumping of groundwater to allow the construction of basements.
A number of residents have raised issues very similar to yours, and we have created a website
to address them: Recycled Water Web Page . Scroll down to the last line and click on “here” to
see our “Frequently Asked Questions” about the pumped ground water.
While I know it appears to be wasting water, the shallow ground water aquifer is flowing to our
creeks and Bay. The pumping and discharge of this shallow ground water to the storm drains
sends the ground water to the same place, our creeks and Bay, where it supports ecosystems
and their wildlife. Nonetheless, the City is working with builders to try to get as much of water
used as practical. The main limitations are the very high cost of trucking the water and the lack
of a piping system from the pumping sites. Farmers are just too far away to make their using it
practical at this time. A portion of the water is being used to water City trees, provide dust
control at construction sites, and similar non-potable uses.
With respect to the potential for drawing down the shallow groundwater and causing land
subsidence, we do not have reason to believe this would occur, given the short duration
pumping and the small number of wells involved here. Subsidence can occur when pumping
happens over a number of years from many wells.
I hope this helps address your concerns.
Phil Bobel
Assistant Director, Public Works
From: Shikada, Ed Sent: Wednesday, July 15, 2015 8:07 AM To: Georgia Relman Cc: Council, City; Bobel, Phil Subject: Re: draining ground water
Dear Ms. Relman,
Thanks for contacting us with your concerns. I will ask Public Works staff to review the issue
and reply directly to you. There has been quite a bit of activity on this issue recently that may
interest you, specifically on the topics you raised. You may also wish to participate in future
discussions.
Sincerely,
Ed Shikada
Assistant City Manager
On Jul 14, 2015, at 4:12 PM, Georgia Relman <georgiarelman@gmail.com> wrote:
Hi All,
I have a question. Just in our neighborhood alone (around professorville), 4 construction sites
building private homes are draining ground water at full blast down storm drains; this has been
going on for many MONTHS now.
Why are private construction companies allowed to drain Palo Alto ground water? Wouldn't it be of benefit to use this water for Palo Alto parks etc. or sell it to farmers for Palo Alto profit
(because it is needed)?
When the ground water is drained under Palo Alto, will the ground sink as it has in other areas of
California as they are being drained of ground water?
Why is this not of concern to our city government? (I don't get it)
Sincerely,
Georgia
On Apr 25, 2015, at 2:32 PM, Skip Shapiro <sailorskipca@yahoo.com> wrote:
Dear Mayor Holman and City Council,
This is a request for the Planning Department and the City Council to take immediate action to
stop groundwater pumping which occurs during the construction of residential basements.
As long time Palo Alto residents, we are appalled to see millions of gallons of groundwater
going down storm drains in the midst of this historic California drought. At the same time,
residents and businesses have been asked to curtail water use for landscape and other uses. Even
worse, the pumping depletes groundwater that is essential to the health of trees, causes
subsidence that can damage property, and consumes water Palo Alto relies upon for emergencies.
This morning we passed a home under construction on Harker where groundwater is being
pumped. We estimated the flow rate to be 75 gallons per minute (based on the fill time of a 5
gallon bucket), which equates to 108,000 gallons – or 14,400 cubic feet – per day. From past
experience monitoring similar groundwater pumping for basement construction, the pumping will continue for at least 4 weeks. That amounts to more than 400,000 cubic feet of wasted water.
Residential basement construction is a relatively recent phenomenon in Palo Alto, driven by
people maximizing living space within lot coverage constraints. It has likely contributed to the
steep increase in property values and encouraged buyers who raze existing houses to replace
them with new ones that include basements…without considering the impact on neighbors, the community, and the environment.
We think it’s time to halt approval of residential construction that includes basements where
groundwater pumping is required. Basements should not be allowed on these sites. We request
an immediate moratorium on design and construction approval for any home where groundwater
pumping is required. We also ask the City Council to direct the Planning Department to review and change regulations that permit residential basement construction.
Respectfully,
Barbara and Skip Shapiro
Mr. James Keene
General Manager
City of Palo Alto
250 Hamilton Avenue
Palo Alto, CA 94301
Dear Mr. Keene,
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Valoran P. Hanko --r ' . c, rvvk-·on
864 Fielding Court uOJ)\ ce l)'KJ ).j.)\J 1
Palo Alto, CA 94303-3645
May 19, 2015
I recently noticed a pumping operation in my neighborhood at 804 Fielding Drive that is reminiscent of an
operation that occurred next door at 858 Fielding Ct in 2001. This pumping operation takes ground water from our
underground aquifer and sends this to the storm drain as undesirable waste in preparation of a new residential
construction. When this operation was performed in 2001, the surrounding neighborhood sank in elevation
resulting in a new designation for the neighborhood to be within the 100 year flood zone, where as prior it was
not. Additionally, this resulted in cracks in the pavement of our street where the sinking of the ground is still
evident. Additionally, it was observed by some neighbors that their house slab foundations (characteristic of the
1940's period-build homes) had shifted and cracked. The house behind us had their garage drop in elevation in
one of their corners. I estimate that non-potable water is being pumped at a rate of about 0.5 gal/sec, which
equates to 30 gallons per min, 1800 gal per hour, 43,200 gal per day, 302,400 gal per week. Since this operation
went for about 6 months at the next door neighbor's site, assuming a constant rate, this amount of water would
be equivalent to (at 1.2 million gallons of water per month) 7.2 million gallons of underground water. Since the
volume of water occupying 1 gallon is 0.134 cubic feet per gal (7.48 gal per cubic feet), 7.2 million gallons would
take 970,000 cubic feet of underground aquifer space, and it is a fact that when the ground collapses into this
aquifer space, it can never be retrieved again. The loss of elevation in the neighborhood places financial burden
upon innocent people, causing many with mortgage payments to be required to have FEMA Flood Insurance, and
even those who own their house, puts them at new risk of flooding. I believe this pumping action, apparently
approved by the City Building Department, has not been seriously evaluated for its consequences by qualified
engineers without bias. Furthermore, this precious water is being wasted into the storm drain during a severe
drought, another irresponsible action. I am not sure about the legal consequences of halting this operation in my
neighborhood, but as General Manager you must have some power to take emergency actions when severe
consequences can be seen or is discovered, and thus this letter is to inform you of this matter with the hope that
you can stop this pumping process and new building permit approvals, and to suspend all current operations until
appropriate state-of-the-art engineers have evaluated this type of operation. Meanwhile, I intend to contact the
Santa Clara County Water Resources Board about this concern, and hope you may work together with them to
seek a resolution that does not adversely impact the community, one that includes the preservation of our
underground aquifer.
//~.:c•r•I:? / /fj ~~/ / ~···
1. c{c:~ l~ i
Valoran P. Hanko ·
PUBLIC WORKS
CITY OF P.O. Box 10250
PALO
ALTO
Palo Alto. CA 94303 ·
650.329.2151
July 6, 2015
Valoran P. Hanko
864 Felding Court
Palo Alto, CA 94303-3645
Dear Mr. Hanko:
Thank you for your May 19 letter concerning the impacts of basement construction groundwater
pumping. I've been asked to respond on behalf of Palo Alto City Manager Jim Keene. Your letter
expresses concern about a current pumping site and one that took place in 2001, both in your
neighborhood.
With respect to the earlier pumping, you expressed the belief that the pumping caused the ground
to subside. We do not have reason to think that is the case. The additions to the flood zone that
were made around that time were the result of new, better data, as opposed to any anticipated
change in actual elevations. The earlier flood zone map had been based on a more limited set of
elevation measurements. When more elevation data was collected in the 2000 time frame, it
resulted in relatively small shifts in the flood zone boundary, but ones which were very important
to the individual houses affected. You calculated the rough amount of ground water pumped out
and postulated that that the ground level would sink to a level associated with that loss of water.
We do not believe that would be the case. Rather, the groundwater is moving and new ground
water would fill behind the groundwater being pumped out. Only a large number of wells
operating over a long time frame would cause a relatively permanent change in the ground water
elevation and an associated ground level subsidence. As you know, subsidence has occurred in a
number of areas where large numbers of wells have pumped over time.
You also expressed the view that the pumped water going to the storm drain was being wasted.
And yet this ground water was moving toward our creeks and Bay and ultimately would have
replenished both. Pumping some of it to the storm drain results in it traveling a different path, but
ultimately reaching the same locations: our creeks and Bay. Our creeks and Bay need this water to
preserve ecosystems and maintain needed salinity levels.
Nonetheless, because of the strong feelings of a number of our residents, we are working to have
builders minimize the amount pumped and use as much of the water as practical. Builders are now
required to build "Fill Stations" at their sites so that others can fill trucks and tanks and use the
water. The current pumping site at 804 Fielding near you has a Fill Station. The City, other builders
and residents like you can use the water. Please see our website for the other locations and
contact information: www.cityofpaloalto.org/water.
C ityOf Pa lo A lto.org
Printed with soy-based inks on 100% recycled paper processed without chlorine.
I hope this addresses your concerns. Please do not hesitate to contact Mike Nafziger (650-617-
3103) for more information about 804 Fielding, or myself (650-279-0464) for broader issues we
are facing in this most difficult time of drought.
Sincerely,
cfi?:f il,&t
Phil Bobel
Assistant Director, Public Works
From: "Andrei Sarna-Wojcicki" <andreisarna@gmail.com<mailto:andreisarna@gmail.com>>
To: "Council, City" <city.council@cityofpaloalto.org<mailto:city.council@cityofpaloalto.org>>,
"letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com>"
<letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com>> Cc: "Deborah Harden" <deborahrharden@gmail.com<mailto:deborahrharden@gmail.com>>
Subject: Fwd: Groundwater is wasted by pumping at construction sites and dumping into storm
sewers
To: Mayor of the City of Palo Alto and the City Council:
I have sent this message to the Public Comment web site two of days ago, but have not received
an answer, and the matter is urgent. I have also sent it previously to the Palo Alto daily news site
(letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com>). So, I'm forwarding this
email to you and the City Council. By now, three days have elapsed since I sent the first message, and an estimated minimum of 260,000 gallons of groundwater have been pumped from the construction site at 2133 Webster and dumped into the storm sewer at the corner of N.
California and Byron Streets. The water continues to be pumped as I write this (I just went by
there a few minutes ago).
Putting up a sign saying that the public can help themselves to the water does not solve the problem of this wasteful practice, continued with city approval during a time of extreme
drought. As I mentioned in the message, this is just one of several construction sites in the city
where pumping of groundwater is going on. This is a wasteful practice during ordinary times,
and more so during the current severe drought. The water needs to be used for watering the trees and green areas of the city, and to maintain the level of the groundwater to keep city and residential trees from dying.
The excavation at the Webster site must be at the site of a buried old gravel channel, to account
for the high discharge. The water that is being wasted by direct dumping into the storm sewers not only deprives the trees in the vicinity of the pumping and downstream in the water table, but it also depriving a whole ecosystem at lower elevations downstream in the water table to the
southeast--the marshes and the city Baylands.
This is a high price to pay for allowing cellars to be built in an area that is at low elevations (the Webster St. site is at ~17 feet above sea level). Another several such construction sites have been recently finished near our house on Garland Drive. These are at an even lower elevation,
10 to 15 feet. Building cellars in these areas is a mistake, and has been historically avoided in
this area since early European settlement for very good reasons. The water table here is high and
irregular in elevation. Some of the new cellars actually intrude below the water table, as appears to be the case at the Webster Street site.
I urge you to take this matter under advisement. Additional comments and arguments are
provided in the forwarded email.
Sincerely,
Andrei M. Sarna-Wojcici,
Resident of Palo Alto (708 Garland Drive)
Retired geologist, U.S. Geological Survey
---------- Forwarded message ----------
From: Andrei Sarna-Wojcicki <andreisarna@gmail.com<mailto:andreisarna@gmail.com>>
Date: Thu, May 7, 2015 at 10:41 AM
Subject: Groundwater is wasted by pumping at construction sites and dumping into storm sewers
To: letters@dailynewsgroup.com<mailto:letters@dailynewsgroup.com> Cc: Deborah Harden <deborahrharden@gmail.com<mailto:deborahrharden@gmail.com>>
Dear Sir or Madam:
Groundwater is being wasted on the Peninsula by being pumped out at construction sites and dumped into city storm sewers. This practice is actively going on at at least three construction
sites in Palo Alto, and probably at many more throughout the Peninsula.
I passed by one such site at 2133 Webster St. in Palo Alto at ~10:45 AM yesterday, returned by
there at ~12:45 noon, and passed by there again at ~5:45 PM. The water was going full blast the whole time from the construction site, around the block to N. California and Byron streets, and
down into a storm sewer. I estimated that about a gallon of water was dumped every second
from a six-inch diameter pipe, which would amount to about 25,200 for the 7 hours time of my
observation. This is probably a minimum for this particular site for this day. At the calculated
rate, this would amount to 86,400 gallons of water for a 24 hour period. My wife observed the same practice going on a few months ago from another site, for at least a week.
This is a massive waste of groundwater during a period of severe drought. It depletes water from
an already depleted water table, forming a cone-shaped depression around the pumping site, and
decreasing the available groundwater in that area from flowing farther down in the water table toward lower elevations, thus lowering the water table and depriving trees from water. It's
killing off our trees.
This water needs to be used for watering the trees and other plants in the municipal parks and
other public grounds, and any left over water should be made available for residential use. Reservoirs need to be constructed to store this water, and a distribution system be put into
place, perhaps even by temporary above-ground plastic pipe systems during this drought, to
make use of this water.
At the dump site that I observed, a sign put up by the city of Palo Alto which informs the public that the water is not potable, that it is being discharged (no duh), and states that "...To use this
water for irrigation pr other non-potable purposes, follow this discharge hose back to the water
filling station." I presume this refers to the pumping site at 2133 Webster. And what does the
Palo Alto citizen do then? Bring a Dixie Cup and help himself/herself to the water? Or back-up
a tanker truck to the site and fill-up? This is obviously a large job that the Peninsula municipalities need to address.
I sent a message regarding this situation to the city of Palo Alto today.
I attach photos from the pumping and dump sites I observed yesterday.
Sincerely,
Andrei Sarna-Wojcicki,
Resident of Palo Alto
Comments to Council regarding Dewatering Residential Basement Construction
Keith Bennett
November 9, 2015
The City of Palo Alto has a history of developing policies to protect natural resources, to protect
our environment and to encourage sustainability. Water is now recognized as a valuable and
limited resource, and groundwater is an important component of the City of Palo Alto’s
Emergency Water Supply. Climate change is predicted to increase the risks of droughts,
megadroughts and floods, in addition to sea (and Bay) level rise.
https://www.washingtonpost.com/national/health-science/todays-drought-in-the-west-is-
nothing-compared-to-what-may-be-coming/2015/02/12/0041646a-b2d9-11e4-854b-
a38d13486ba1_story.html
1) The Groundwater Supply Feasibility Study performed by Carollo Engineers for the City of
Palo Alto in 2003 provides quantitative analysis and measurements of the effects of
groundwater pumping in Palo Alto. Data from the pumping in 1988 of groundwater for
local domestic water use was deemed to be the most reliable and is the primary basis for
the conclusions of the report, which is available at:
http://www.cityofpaloalto.org/cityagenda/publish/uac-meetings/1930.pdf
Some main points are summarized below. In this section, quotes indicate verbatim text
from the study, italics indicate my personal analysis using other information including map
data. Text not in quotes are my personal summaries of information from the study.
a. “Utilizing the data from the 1988 pumping, the extraction of 1,000 acre-feet from
the Palo Alto area will result in basin-wide water level declines on the order of 15
feet.” --- pg. 20
The shallow surface aquifer level, typically a few feet below the ground surface,
declines in response to pumping the deeper aquifer as shown by the well level graphs.
--- pgs. 5 - 10
b. The water levels in the Fernando, Middlefield and Matadero wells were lowered by
18, 25 and 37 feet respectively, even though water was not pumped from any of
those wells. --- Table 1, pg. 13
An interactive map showing the locations of the wells and 2015 basement
dewatering sites is attached (Map A) with this document and available online at:
https://www.google.com/maps/d/edit?app=mp&hl=en_US&mid=zW7thpaYaYZI.kYz
YfTCRxd_Q
The Middlefield well is located about 5 blocks (0.4 miles, straight line) from the
Rinconada Well (from which 600 acre-feet of water was produced in 1988) and about
0.7 miles from the Hale Well (produced 400 acre-feet in 1988).
Peers Park (produced 400 acre-feet) is the closest well to the Fernando and
Matadero wells and is 1.0 – 1.2 miles away.
c. “Depending on the method, estimates of average annual recharge to the basin are
between 38 and 3,800 acre-feet. “ -- Pg. 20
d. “The year-to-year 500 AFA* extraction is intended to not lower groundwater levels
substantially, which would preserve the natural groundwater flow direction and
prevent saltwater intrusion. The periodic 1,500 AFA well use described above
would result in transient occurrence of water levels below sea-level. While water
level below sea-level will reverse the seaward gradient, the slow travel time of
groundwater provides a buffer from seawater intrusion for transient use. “ – Pg. 21
* AFA = Acre-feet annually.
2) The total amount of groundwater pumped for residential basement construction in 2015 is
estimated to be about 400 acre-feet, based upon an average of 1.2 million cubic feet (28
acre-feet) per basement for the 14 basements dewatered in 2015.
3) The Groundwater Supply Feasibility Study estimates that the water table is lowered
approximately proportionately to the amount of water pumped. Using the value in the
report of 15 feet lowering for 1,000 acre-feet pumped, the estimated lowering of the water
table due to dewatering for residential basement construction in 2015 would therefore be
about 6 feet, and would extend over large areas of Palo Alto.
4) An advisory Measure N, “Emergency Underground Water Storage and Equipment
Replacement,” (November 2007) passed with 91.84% of the vote. The Emergency Water
Supply Project (EWSP), WS-08002, was approved by Council in 2007 and bonds totaling
$35,015,000 were sold on October 6, 2009. Of this amount, approximately $5.36 million
was used for projects related to using groundwater: groundwater feasibility studies (CMR
124:06 and related), rehabilitation of existing wells (CMR 232:10) and construction of new
wells (CMR 371:09). The bonds are being repaid over 25 years through water usage fees.
5) As part of the EWSP, five existing wells have been rehabilitated for use as emergency
domestic water supplies. These wells are the Hale Well (999 Palo Alto Avenue), Rinconada
Well (1440 Hopkins Avenue), Peer’s Park Well (1899 Park Boulevard), Matadero Well (635
Matadero Avenue) and Fernando Well (410 Fernando Avenue).
http://www.cityofpaloalto.org/gov/depts/utl/eng/water/wells/faq/rehabilitation.asp
Additionally, two new wells have been constructed, one at Eleanor Pardee Park and another
at (Rinconada) Library / Community Gardens.
http://www.cityofpaloalto.org/gov/depts/utl/eng/water/wells/eleanor.asp
Two 2015 dewatering sites are within the triangle formed by the two new wells (Eleanor
Pardee Park and Library / Community Gardens) and the Rinconada well. See attached Maps
B and C or online map.
https://www.google.com/maps/d/edit?app=mp&hl=en_US&mid=zW7thpaYaYZI.kXmqQlQL
K9iM
6) Methods exist for residential basement construction that do not require dewatering.
Residential basements are built in areas of high groundwater in The Netherlands without
dewatering, per personal verbal communication with the mayor of Palo Alto’s sister city,
Enschede at the Council Meeting on November 2.
Map A: Palo Alto Emergency Water Supply Well Map
Locations of Palo Alto's
Emergency Water Supply
Wells, including the
Middlefield Well.
Basement dewatering sites
Emergency Water Supply Wells
Rinconada Well
Hale Creek Well
Peers Park Well
Matadero Well
Fernando Well
Eleanor Pardee Park Well
Library Community Gardens
Well
Historical Wells
Middlefield Well
Map B: Dewatering_Map 2015
Residential basement construction dewatering sites and emergency water supply well
locations
2015 Basement dewatering sites
2133 Webster St
2130 Byron St
713 Southampton Dr
897 Southampton Dr
736 Garland Dr
684 Wellsbury Way
804 Moreno Ave
1812 Bret Harte St
1210 Newell Rd
51 Jordan Pl
2230 Louis Rd
1405 Harker Ave
3832 Grove Ave
1950 Newell Rd
Emergency Water Supply Wells
Rinconada Well
Hale Creek Well
Peers Park Well
Matadero Well
Fernando Well
Eleanor Pardee Park Well
Library Community Gardens
Well
Map C: Dewatering_Map 2015 (Community center zoom)
Residential basement construction dewatering sites and emergency water supply well
locations
2015 Basement dewatering sites
2133 Webster St
2130 Byron St
713 Southampton Dr
897 Southampton Dr
736 Garland Dr
684 Wellsbury Way
804 Moreno Ave
1812 Bret Harte St
1210 Newell Rd
51 Jordan Pl
2230 Louis Rd
1405 Harker Ave
3832 Grove Ave
1950 Newell Rd
Emergency Water Supply Wells
Rinconada Well
Hale Creek Well
Peers Park Well
Matadero Well
Fernando Well
Eleanor Pardee Park Well
Library Community Gardens
Well
Attachment F
November 2, 2015
To: Palo Alto City Council
From: Keith Bennett
Save Palo Alto's Groundwater
Re: Petitions
Attached are petitions signed by 190 individuals specifically requesting a moratorium on new
dewatering permits for residential basement construction. The signatures were mostly collected during
a short 2 - 3 period in late summer by a handful of volunteers.
Name
Deborah Baldwin
Henry Heller
M Smith
City
Menlo Park
Palo Alto
Palo Alto
Postal Code Signed On
94025 8/6/2015
94303 8/7 /2015
94301 8/7 /2015
City of Palo Alto
GROUNDWATER SUPPLY
FEASIBILITY STUDY
FINAL
April 2003
2700 YGNACIO VALLEY ROAD, SUITE 300 • WALNUT CREEK, CALIFORNIA 94598 • (925) 932-1710 • FAX (925) 930-0208
H:\Final\PaloAlto_WCO\6589A00\Rpt\GWSupplyFeasibilityStdy-Final.doc
CITY OF PALO ALTO
GROUNDWATER SUPPLY FEASIBILITY STUDY
TABLE OF CONTENTS
Page
1.0 INTRODUCTION .......................................................................................................1
1.1 Background .....................................................................................................1
1.2 Well System Rehabilitation and Construction Plans........................................2
2.0 POTENTIAL GROUNDWATER USE IN PALO ALTO...............................................2
3.0 HISTORICAL GROUNDWATER LEVELS AND USE................................................4
4.0 ESTIMATION OF BASIN CAPACITY......................................................................11
4.1 1988 Drought Pumping Analysis ...................................................................12
4.2 Summary of Basin Capacity Estimation ........................................................13
5.0 POSSIBLE PALO ALTO GROUNDWATER SUPPLY SYSTEM.............................14
6.0 POTENTIAL IMPACTS OF GROUNDWATER EXTRACTIONS .............................15
6.1 Subsidence....................................................................................................16
6.2 Saltwater Intrusion.........................................................................................18
6.3 Contaminant Plume Migration .......................................................................19
7.0 SUMMARY...............................................................................................................20
LIST OF TABLES
Table 1 Water Level Response ..................................................................................13
LIST OF FIGURES
Figure 1 Existing and Proposed City Wells...................................................................3
Figure 2 Hale Well.........................................................................................................5
Figure 3 Matadero Well.................................................................................................6
Figure 4 Fernando Well.................................................................................................7
Figure 5 Peers Park Well ..............................................................................................8
Figure 6 Rinconada Well...............................................................................................9
Figure 7 Meadows Well...............................................................................................10
Figure 8 Historical Data on Water Use, Supply, and Subsidence in San Jose, CA....17
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City of Palo Alto
GROUNDWATER SUPPLY FEASIBILITY STUDY
1.0 INTRODUCTION
The Palo Alto Utilities Department (Utilities) is presently examining the issues relating to the
use of groundwater. Examining all water supply options, including local sources such as
groundwater supply, is a part of good planning practices for the water utility. Utilities has
engaged Carollo Engineers, P.C. (Carollo) to prepare a “Groundwater Supply Feasibility
Study” (Study) to:
“Evaluate whether operating one or two of the City’s water wells as active supplies
would cause a significant decrease in groundwater levels or deterioration in
groundwater quality.”
This Study estimates the groundwater basin capacity in Palo Alto vicinity, identifies a
possible well supply system given the basin capacity constraints, and examines whether
there is a safe way to use groundwater as a supply source either in drought periods or on
an ongoing basis. We have examined the capability of Palo Alto’s groundwater supply and
some of the more significant potential impacts of pumping. The three potential impacts that
this Study specifically addresses are:
• The risk of land surface subsidence;
• The risk of groundwater contamination through saltwater intrusion; and
• The risk of groundwater contamination through the travel of pollution plumes to the
drinking water aquifer.
Palo Alto Utilities staff and Carollo have worked closely with staff of the Santa Clara Valley
Water District (SCVWD) to ensure that SCVWD staff are fully informed of the analysis
methods and findings. At the present time, the City of Palo Alto is NOT planning to use
any of the wells for long-term supply. Any change from the planned emergency-only
use of the wells would happen only after further detailed analysis, environmental
review, extensive discussion with the public, and approvals by both the Utilities
Advisory Commission and the City Council. Staff is merely examining the issues
related to the groundwater basin and the possible use of the wells in severe
droughts or as a supplemental supply in the future.
1.1 Background
The City of Palo Alto obtained its well system in 1896. The entire water supply for the City
was derived from groundwater until 1938 when it began receiving supplemental supplies
from the City and County of San Francisco. In 1962, the wells ceased operating on a
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continuous basis and San Francisco water became the City’s primary source of supply with
the wells maintained as an emergency water supply. The wells were last used in 1988 and
1991 to provide supplemental supplies during a serious drought. At this time, the City
maintains five wells as emergency (standby) water sources, but they are in need of
rehabilitation.
1.2 Well System Rehabilitation and Construction Plans
The City is presently implementing plans to rehabilitate the five existing wells and build
three new wells. These improvements are part of a larger Water System Capital
Improvement Plan, which was developed as a result of extensive study completed in 1999
(1999 Study). The primary purpose of the well rehabilitation and construction plans is to
provide necessary emergency water supplies in the event of a complete cutoff from the
SFPUC water supplies.
The overall water CIP has been reviewed and approved by both the Utilities Advisory
Commission and the Palo Alto City Council. Funds for the improvements are included in the
five-year Water Capital Improvement Program Budget.
2.0 POTENTIAL GROUNDWATER USE IN PALO ALTO
The imported water purchased from the SFPUC has been a reliable supply for 40 years.
There is growing concern, however, that this supply may be jeopardized either partially or
completely by a number of factors. For example, the SFPUC supply was rendered
unavailable once in 1995 and again in 1998 due to water quality concerns.1 In addition,
recent studies conducted by the SFPUC have identified a number of system vulnerabilities
that could cut off the water supply for up to 60 days in the event of a serious emergency.2 In
regards to long-term reliability, the SFPUC supply is insufficient to meet the current and
forecasted needs of the users of the regional system it operates. Droughts in 1976-77 and
1987-1992 that resulted in the rationing of supplies clearly illustrates this fact. The SFPUC’s
Water Supply Master Plan (WSMP) recognized that on a long-term basis, its supplies are
inadequate. The WSMP identified the system’s yield as 239 mgd while current demand is
greater than 260 mgd and the demand estimate for 2030 is 303 mgd, or a shortfall in
supplies of 64 mgd. Thus, it is prudent for the City to evaluate its options for improving the
reliability of its water supply.
The location of the City’s wells is shown in Figure 1. These wells may have potential uses
beyond supplying water during SFPUC outages. If the City Council decided, the wells could
also help supplement water supplies during drought periods and perhaps even as active
1 “Water Wells, Regional Storage, and Distribution System Study,” page 4-1, prepared for the City of
Palo Alto by Carollo Engineers, P.C. dated December 1999. 2 SFPUC fact sheet dated August 5, 2002.
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LEGEND
Pa303f1-6589.cdr
Figure 1
EXISTING AND PROPOSED CITY WELLS
GROUNDWATER SUPPLY FEASIBILITY STUDY
CITY OF PALO ALTO
SFPUC Turnout
Existing Well Sites
Proposed Well Sites
No Scale
Matadero
Well
P ers Pa k e r
Wlel
Rinconada
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Library/
Community
Gardens Well
El Camino
Park Well
Palo Alto
Medical Facility
Well (Roth Site)
Middlefield
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Park Well
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Well
tt
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California
Turnout
Lytton
Turnout
sources to be regularly used in conjunction with the SFPUC supply. These uses, however,
raise significant concerns related to lowering of the groundwater levels. Significantly,
depressed groundwater levels can potentially lead to environmental consequences such as
subsidence, saltwater intrusion, and contaminant migration. Though there may be other as
yet unidentified impacts, these impacts are discussed in this Study as they are considered
to be the most significant potential impacts.
Currently, the wells are designated standby sources meaning that they can only be used
15 days a year and no more than 5 days consecutively.3 The “standby” designation is made
with the California Department of Health Services (DHS) in part because the well water
quality exceeds some secondary (aesthetic) drinking water standards. According to the
1999 study, the well water quality exceeds secondary standards for TDS, iron, and
manganese.
For the purposes of this Study, it is assumed that the water would be used for potable uses.
As such, changing the well status with the DHS from “standby” to “active” would require the
well water to be treated such that it met all drinking water regulations. Alternatively, the
regulations allow the City to distribute water that meets primary drinking water quality
standards but exceeds some secondary drinking water quality standards. Proceeding in this
manner would require the City to first complete a study acceptable to the California
Department of Health Services (DHS) showing consumer acceptance of water not meeting
secondary drinking water standards (see California Code of Regulations Title 22, Division 4,
Chapter 15, Article 16, Section 64449 for specific details).
Customer acceptability, however, may require the City to install sufficient treatment at the
wells to be used for drought or active supply such that the water quality is increased
significantly or made comparable to the SFPUC water. This issue was covered in the City’s
“Long-Term Water Supply Study” dated May 2000 (May 2000 Study).
3.0 HISTORICAL GROUNDWATER LEVELS AND USE
The best way to evaluate the effect that pumping has on groundwater levels is to review
historical data that show the basin’s response to pumping. Groundwater pumping and water
level data from 1950 through 2000 are presented in Figures 2 through 7. All of the water
level graphs show a characteristic rise following the switch to SFPUC water in the early
1960s.
In general, the graphs show smooth trends in response to recharge, pumping, and drought
conditions. There are occasional spikes in the graphs that appear to be outlying, erroneous
3 According to the California Code of Regulations, Title 22, Section 64449, (e) (I), standby wells may
be used as active sources without additional water treatment if the City were to conduct a study
establishing the customers’ willingness to accept water that doesn’t meet secondary water quality
standards.
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Pa303f2-6589.cdr
Figure 2
HALE WELL
GROUNDWATER SUPPLY FEASIBILITY STUDY
CITY OF PALO ALTO
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CITY OF PALO ALTO
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CITY OF PALO ALTO
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data. We believe that the occasional spikes in the data are more likely due to equipment
error than due to the actual water level. The information presented in the graphs is used in
the following section to estimate the groundwater basin capacity in the Palo Alto area.
4.0 ESTIMATION OF BASIN CAPACITY
Groundwater resources of the Palo Alto area occur within a much larger aquifer system -
the Santa Clara Valley Groundwater Basin. This basin extends as far south as Coyote
Narrows and extends north of Palo Alto far into San Mateo County. The system is bounded
by uplifted bedrock to the west. To the east, the shallow portion of the aquifer system is
bounded by San Francisco Bay. At depth, the aquifer systems of the west side of the valley
interfinger under the bay with those of the east.
In a large groundwater basin, estimation of the capacity of a smaller area within a basin is
difficult because the smaller area is, by definition, unbounded. Groundwater moves freely
between basin areas in response to hydraulic head. Therefore, pumping or recharge in one
area of the basin has effects on the basin as a whole. Indeed, the impacts of seasonal
variations in recharge and in extractions by one or more of Palo Alto’s neighbors are
evident in the seasonal rise and fall of the water levels at the Hale Well.
Estimating the capacity of the Santa Clara Valley Groundwater Basin in the Palo Alto area
requires the definition of an arbitrary area for purposes of evaluating changes in
groundwater storage that have occurred. For the purpose of estimating the storage capacity
of the groundwater basin in the Palo Alto area, an arbitrary area was defined. This area is
bounded on the west by the Hanover Fault zone that is approximately 2,000 feet west of
El Camino Real with a similar trend. The Bay was adopted as the eastern boundary. The
Hanover Fault zone separates the alluvium of the basin from the bedrock to the west and is
a hydrogeologic boundary. For the upper portion of the aquifer system that is in hydraulic
communication with the Bay, the Bay is a hydrogeologic boundary. For the deeper portions
of the aquifer system, the Bay is not a hydrogeologic boundary but for purposes of definition
in this Study, it was adopted as a boundary. The adopted north and south bounds are San
Francisquito Creek and San Antonio Road, respectively. The area described by these
boundaries is approximately 9,500 acres.
Given this defined area, there are several approaches to understanding the capacity or
yield. Three methods were evaluated in a previous report to the City entitled “Estimation of
Groundwater Basin Capacity” dated December 2002 (December 2002 Report). Those three
methods are: 1) Use of the SCVWD calibrated groundwater model; 2) Analysis of basin
recovery to cessation of pumpage; and 3) Analysis of basin response to 1988 drought
pumping.
Once the December 2002 report was completed, the City and Carollo met with
representatives of the SCVWD to discuss their questions and concerns regarding the
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report. One of the outcomes of that meeting was that the first two methods of calculating
the groundwater basin capacity were controversial for the following reasons:
• The SCVWD groundwater model does not accurately reflect the hydrogeologic
conditions at Palo Alto. One of the most important deviations is that the model does
not account for any recharge from San Francisquito Creek. In fact, the model has a
boundary condition that sets the contribution at zero. As such, using the model to
calculate the Palo Alto groundwater basin capacity would likely result in a volume that
is erroneously low unless the contribution from San Francisquito Creek is accounted
for. Since this data is not available and obtaining it would not only require an
extensive hydrogeologic study but would also raise concerns regarding the amount of
water that must be left in the creek versus that which can be considered useful for
groundwater recharge and later extraction, this method will not be further developed.
• Using the groundwater level recovery history to calculate the basin storage capacity
yielded values that ranged over two orders of magnitude. SCVWD representatives
recommended that the City should perform multiple aquifer tests to improve the
accuracy of this data. However, the existing condition of the City’s wells is not readily
conducive to performing this type of test. In addition, an aquifer test could readily be
performed once the City has completed upgrading its wells. For the present time, this
method of estimating the basin capacity will not be pursued.
The third method presented in the December 2002 Report for estimating the groundwater
basin capacity (i.e. analyzing the water level data gathered during and after pumping in
1988) will be used for the remainder of this Study.
4.1 1988 Drought Pumping Analysis
The pumping performed by the City of Palo Alto during the drought provides data to directly
estimate the response of the basin to extractions. When the 1987-1992 drought occurred,
the City’s wells had been essentially idle since 1962. During this period, water levels in the
basin had risen, on average, more than 150 feet. Approximately 90 percent of that recovery
took place in the first 10 years following cessation of pumping. The City operated the wells
for an approximately 5-month period in 1988 and extracted approximately 1,505 acre-feet.
The water level response is shown on Figures 1 through 6. The extraction volume and the
observed water level response are summarized in Table 1.
Averaging the observed water level declines results in an average decline of approximately
24 feet. This water level decline reflects Palo Alto’s pumpage while also reflecting the
simultaneous pumpage from neighboring utilities. Utilizing the observed 24 feet of decline
across the assumed 9,500-acre area results in an observed coefficient of storage of
approximately 0.007 (dimensionless). This value is quite appropriate for a semi-confined
aquifer system, such as the Palo Alto area.
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Table 1 Water Level Response
Groundwater Supply Feasibility Study
City of Palo Alto
Well
1988 Extractions
(acre-feet)
Observed Water Level Decline During the
1988 Pumping Period (feet)
Matadero 0 18
Hale 398 15
Fernando 0 25
Rinconda 627 25
Middlefield(1) 0 37
Meadows(2) 123 Data Not Available
Peers Park(3) 357 Data Not Available
Total 1,505 Average = 24
Notes:
(1) Middlefield well water level decline likely reflects proximity (about 0.5 mile) to the
operating Rinconda well. Similar effects are revealed for the Matadero and Fernando
wells indicating that they are in the same basin as the operating wells.
(2) The Meadows well was not highly productive and was destroyed following its use in
1988. No water level data was collected after 1988.
(3) Water level data for the Peers Park well were not collected between the years 1988
and 1994. Subsequent data shows water level variation similar to the Hale well.
Though some groundwater was pumped in 1991, the City ceased significant extractions in
December 1988. Of interest is the rapid recovery of the basin after drought conditions, with
water levels recovering to pre-pumping levels within 18 months of the extraction period.
This also is reflective of the semi-confined nature of the basin and the active recharge
efforts of SCVWD.
4.2 Summary of Basin Capacity Estimation
From the drought pumping analysis presented above, the following conclusions are drawn
regarding the groundwater basin capacity:
• Water levels in the Palo Alto area have returned to almost predevelopment levels.
Essentially, the groundwater basin in the Palo Alto area is full.
• Data from 1988 pumping provides a good example from which to appraise
groundwater extraction concepts. 1,500 acre-feet were extracted with limited impact.
Water level impacts were short-lived and water levels returned to pre-pumping levels
within 18 months. If pumping were performed during a non-drought period, the
drawdown would likely be less. Initial drawdown may also be affected by the condition
of the existing casings that may cause otherwise productive portions of the aquifer to
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contribute to the supply. An aquifer test should be conducted following the City’s well
construction and rehabilitation efforts to verify the basin’s response to pumping.
• Utilizing the data from the 1988 pumping, the extraction of 1,000 acre-feet from the
Palo Alto area will result in basin-wide water level declines on the order of 15 feet.
Historical experience suggests that the basin will recover to pre-pumping levels within
a couple years. It is expected that the water level would decline approximately 25 feet
if the City were to extract 1,500 acre-feet in one year.
• Occasional depletion of storage resulting from extractions in excess of annual
average recharge appears to have minimal adverse impacts.
• Seasonal fluctuations in water level record from Hale and Rinconada wells shows that
Palo Alto’s pumpage does not occur autonomously. Palo Alto’s water level appears to
be impacted by pumpers outside of SCVWD jurisdiction.
From the above analysis, it appears that the following groundwater pumping scenario may
be safely supported by the groundwater basin:
• During drought conditions, 1,500 acre-feet may be withdrawn in one year as long as
the aquifer is allowed to recover to pre-pumping levels before pumping is reinitiated.
• 500 acre-feet per year may be withdrawn on a year-to-year basis. This practice,
however, should be discontinued if the groundwater levels continued to drop to levels
that may induce negative environmental impacts (see discussion below on
subsidence, saltwater intrusion, and contaminant plume migration).
The balance of this study is presented assuming the wells are used to supply 1,500 acre-
feet per year (AFA) during droughts, or 500 AFA on a year-to-year or active basis.
5.0 POSSIBLE PALO ALTO GROUNDWATER SUPPLY SYSTEM
A well system that could provide this level of service would need a capacity of about
1,000 gallons per minute (gpm) assuming the well is operated continuously for the year
during the drought operation (1,500 AFA) or 2,000 gpm if the well is operated for only half
the year. In addition, the well site must be able to accommodate the treatment equipment
that may be required for this operation (as discussed above), and the environmental and
public involvement efforts must conclude that installing treatment is feasible at the site. The
May 2000 Study evaluated the existing and proposed well sites in terms of their relative
ability to be used as drought or active supplies. That study provided the following ranking of
the existing wells:
• Hale and Peers Park are the best sites since they are existing wells that are
high-capacity and have adequate adjacent space for treatment equipment.
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• Rinconada is another existing high-capacity well but it lacks the space needed for
treatment equipment (unless the equipment is constructed at the location of the
existing tennis courts).
• Fernando and Matadero do not have adequate capacity or space to be considered
feasible active or drought supply sources.
At the time the May 2000 Study was written, the City had not yet begun to implement the
proposed new well projects. As such, these wells were generally ranked lower than the
existing wells. The proposed well sites were ranked as follows:
• The El Camino Park site was ranked among the highest because of the size of the
site and its proximity to the SFPUC turnouts and the proposed reservoir, which would
facilitate blending the well water with SFPUC water before it is delivered to the
distribution system.
• The Eleanor Pardee Park, the Library/Community Gardens, and the Roth sites
(Old Palo Alto Medical Facility) were ranked high because of the size of each of these
sites.
• The Middlefield Road well site was ranked lowest because it is the most constrained
site.
It should be emphasized that none of the previous studies included performing either the
environmental, public involvement, or other studies that are needed before any of the above
sites can be considered truly feasible for well or water treatment facility construction. The
City’s current on-going efforts (the Phase I and Phase II Water Supply Capital Improvement
Projects) include performing these needed studies.
If treatment or blending are not required, any of the City’s wells could be used for drought or
active use assuming the required approvals (discussed above) are obtained. If, however,
water treatment facilities must be constructed, it would be best to focus on a single site
since only one well is needed to be within the identified capacity limits. In addition, focusing
the permitting and engineering requirements on a single site is the most cost-effective
approach for the City. For a drought supply with treatment, the best existing well sites are
Hale and Peers Park. The best proposed well site for a drought supply source with
treatment is El Camino, though the Roth site, the Library/Community Gardens, and Eleanor
Pardee Park all appear to be feasible sites at this time.
6.0 POTENTIAL IMPACTS OF GROUNDWATER EXTRACTIONS
The potential impacts from groundwater extractions derive from changes in groundwater
flow directions that result from changes in water levels caused by extractions (pumping). As
a preface to the following sections, a brief summary of the history of groundwater levels in
the Palo Alto area and the Santa Clara Valley is presented.
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Groundwater development in the Santa Clara Valley began around 1900. At that time most
groundwater wells in the lower elevations of the Santa Clara Valley were artesian – that is,
flowing at ground surface. As aggregate extractions increased, water levels fell
progressively, subject to climatic variations, reaching depths of as much as 200 feet below
ground surface by the early 1960s. With the importation of water to the Santa Clara Valley
water levels began to recover. In Palo Alto, water levels are currently at elevations
comparable to the 1910s. In wet winters, wells in the Palo Alto area now, if not controlled,
flow at ground surface.
6.1 Subsidence
One of the potential impacts of groundwater extractions is a decrease in the elevation of the
ground surface known as land subsidence. Some of the negative effects of the subsidence
are an increased risk of flooding, and damage to infrastructure. Subsidence has been
associated to areas with significant groundwater pumping, natural gas production, or oil
production. Groundwater is pumped from porous layers with higher hydraulic capacities,
i.e., sand and gravel aquifers. As the pumping occurs, water from the confining layers of the
aquifers is drawn into the porous aquifer. The aquifers consisting of sand and gravel tend to
be incompressible, however, the confining layers may be compressible materials, such as
clay. When the groundwater is pumped from these compressible layers the soils compress
and the surface elevation starts to drop. This decline in elevation is the result of the physical
properties of clay. Clay is comprised of platy minerals that are commonly oriented randomly
within the clay deposit. With the removal of fluid and overburden pressure, the clay particles
rotate such that they orient parallel with the ground surface. This rotation results in a
decrease in vertical thickness of the deposit. The thickness loss is irreversible and the
resulting elevation loss is permanent. However, land subsidence can be arrested with
increased groundwater levels.
In Santa Clara Valley, extractions since the turn of the century resulted in lowering of
groundwater levels as much as 200 feet (-160 below sea-level). This lowering of water level
resulted in as much as up to 12 feet of subsidence in some locations of the Santa Clara
Valley. Subsidence in the Palo Alto area was between 2 and 4 feet. The amount of
subsidence in a given area was a function of the amount of water level decline and the local
geologic conditions. Areas with shallow bedrock experienced less subsidence than those
areas underlain by sediments of substantial thickness.
The relationship between water levels, pumpage, imported water supply, and subsidence
(as measured in San Jose, CA) is shown on Figure 8. As can be seen in this figure,
subsidence generally correlates with periods of falling water levels. Currently, land
subsidence has essentially stopped in the Santa Clara Valley as a result of the increased
groundwater levels resulting from the use of alternative water supplies and basin
management.
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Pa303f8-6589.cdr
Figure 8
HISTORICAL DATA ON WATER USE,
SUPPLY, AND SUBSIDENCE IN SAN JOSE, CA
GROUNDWATER SUPPLY FEASIBILITY STUDY
CITY OF PALO ALTO
As discussed above, the loss of elevation associated with subsidence is the result of the
reorientation of clay minerals within clay deposits. The compaction of these deposits is
essentially irreversible in that when water levels subsequently rise, the clay minerals do not
return to their original orientation. However, since these materials are now compacted, the
lowering of water levels does not result in significant further compaction. If the City’s wells
were used at the capacity limits considered herein, the result would be a transient lowering
of water levels to levels less than 25 percent of the historical lows. As such, use of the wells
should not result in renewed subsidence.
There was no data collection focused on subsidence in the Palo Alto area during the last
use of the wells (in 1988 and in 1991). The closest subsidence measurement station
maintained by the SCVWD is approximately 10 miles to the south of Palo Alto. However,
there are no known anecdotal reports of property damage from renewed subsidence in the
Palo Alto area during this period of well use.
6.2 Saltwater Intrusion
The movement of saltwater into freshwater aquifers is called saltwater intrusion. Under
natural conditions, groundwater flows from areas of recharge on the land to areas of
discharge; in coastal areas these are commonly the ocean or the bay. If groundwater
extractions result in on-land water level elevations below sea-level, groundwater flow
directions reverse and seawater moves from the ocean into coastal aquifers. Although the
most common mechanism of seawater intrusion is the lateral movement of seawater
through the offshore exposure of the aquifer, seawater intrusion can also occur vertically
where depressed water levels in underlying aquifers induce flow from overlying water
bodies into the aquifer. If the overlying water body is saline this also results in a type of
seawater intrusion. This vertical movement of seawater is often distinguished from lateral
movement of seawater by the designation of seawater infiltration.
The coastal portion of the Santa Clara Valley aquifer system has historically been impacted
by both seawater intrusion and seawater infiltration. Groundwater extractions in the Santa
Clara Valley from the turn of the last century until the 1970s resulted in the maintenance of
groundwater elevations that were chronically and increasingly below sea-level. As
previously mentioned water surface elevations in the Palo Alto dropped at as much as
140 feet below sea-level. This resulted in the on-land movement of seawater from the Bay
and in many areas the vertical movement of seawater from Bayland ponds used for salt
harvesting and aquaculture. The rate of intrusion/infiltration is governed by the magnitude of
the gradient: the steeper the gradient, the more rapid the movement of water through the
aquifer. Seawater intrusion and infiltration has been arrested as the result of reduced
groundwater extractions, water importation and basin management efforts.
While currently arrested, seawater intrusion could be reactivated if water levels were again
chronically below sea-level. However, because groundwater moves very slowly, the short-
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term occurrence of below sea-level water levels, while briefly reversing the flow direction,
results in little actual transport of saline groundwater. What transfer does occur, is reversed
when flow directions return to normal. This would be the case for either the emergency
supply operation for which the wells are currently permitted, or the possible drought supply
that is discussed herein.
6.3 Contaminant Plume Migration
Groundwater extraction modifies its natural flow direction. In the vicinity of an extraction
well, groundwater flow directions are altered both vertically and horizontally resulting in the
production of water from the well. Water produced from the well derives from a recharge
area surrounding the well, the size and shape of this recharge area being a function of the
hydrogeology and well design. This recharge area is commonly referred to as a capture
zone of the well.
If there are sources of contamination within the capture zone of a well, the well can become
contaminated. Within an urbanized setting, the potential sources of groundwater
contamination are limited to contamination associated with industrial and commercial land
uses. Predominantly this is in the form of leaky underground storage tanks. This would
include gas stations, industrial solvents from manufacturing or research, and dry cleaners.
As part of the 1999 Study, all sources of contamination known by regulatory agencies were
reviewed to determine the risk to City’s existing wells and proposed new well sites. This
review revealed very few contamination sites in the areas surrounding the existing and
proposed well sites. Most of the existing contamination is in the more industrial portions of
the City – those portions west and south of the downtown area. Fortuitously, these areas
are not the areas of the City with the most favorable hydrogeologic characteristics for water
supply wells.
The only identified contaminated sources in the area near the existing or proposed wells
were the Shell gas station on Alma Street and the City of Palo Alto Fire Station. These
locations are proximate to the proposed El Camino Well, and they both had leaky
underground gasoline storage tanks. Both sites have been cleaned up and closed by the
Regional Water Quality Control Board.
The use of the wells at the capacity limits considered herein will temporarily modify
groundwater flow patterns in the vicinity of the wells creating the potential for capture of
contaminate plumes. However, based on available records there are no known contaminate
plumes within the capture zones of the City’s existing or proposed wells.
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7.0 SUMMARY
Once refurbished, the City’s five existing wells and the three proposed new wells will
provide an excellent standby water source to be used during water supply emergencies
such as a shutdown of the SFPUC system. If the Palo Alto City Council decided to use the
wells during droughts or as supplemental sources to be used in conjunction with the
SFPUC supply, the wells could also provide added benefits in terms of enhancing the
reliability and redundancy of the City’s water supply. Any regular use considered in the
future, however, should not exceed the reliable capacity of the groundwater basin to avoid
such negative environmental consequences such as subsidence, saltwater intrusion, and
contaminant migration.
Groundwater pumping and water level data for the last 50 years were analyzed to help
evaluate the basin’s response to pumping. It should be noted that the data collection and
analysis is too limited to draw firm conclusions regarding the reliable basin capacity or
sustainable yield that the City may be able to pump on an active basis. In addition, these
values could only be derived after analyzing and accounting for natural recharge patterns
and the pumping plans of the City’s neighboring utilities. To provide an initial analysis on
issues related to other-than-emergency use of the wells, however, the following may be
inferred from the data analysis presented herein:
• Water levels in the Palo Alto area have returned to almost predevelopment levels.
Essentially, the groundwater basin in the Palo Alto area is full.
• Depending on the method, estimates of average annual recharge to the basin are
between 38 and 3,800 acre-feet. A conservative year-to-year value is likely on the
order of 500 AFA.
• Data from 1988 pumping provides an example from which to appraise groundwater
extraction concepts. 1,500 acre-feet were extracted with limited impact. Water level
impacts were short-lived and water levels returned to pre-pumping levels within
18 months. If pumping were performed during a non-drought period, the drawdown
would likely be less. These values should be revisited through an aquifer test
performed following the City’s well construction and rehabilitation efforts.
• Utilizing the data from the 1988 pumping, the extraction of 1,000 acre-feet from the
Palo Alto area will result in basin-wide water level declines on the order of 15 feet.
Historical experience suggests that depending on climatic conditions, the basin will
recover to pre-pumping levels within a year or so. It is expected that the water level
would decline approximately 25 feet if the City were to extract 1,500 acre-feet in one
year. This decline, however, is not likely to induce significant detrimental
environmental impacts since it is much less than the historical drawdown levels and is
transient in duration.
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• Occasional depletion of storage resulting from extractions in excess of annual
average recharge appears to have minimal adverse impacts.
• Seasonal fluctuations in water level record from Hale and Rinconada wells show that
Palo Alto’s pumpage does not occur autonomously. Palo Alto’s water level appears to
be impacted by pumpers outside of SCVWD jurisdiction, possibly Menlo Park and
East Palo Alto. Under drought conditions, impacts of all local pumpers will be
superimposed on water level conditions.
The limited analysis suggests that sustained year-to-year extractions of approximately
500 AFA may be possible with negligible water level decline. The actual extraction value
would be dependent on the location and depth of the well, how many wells were being
operated, and the extent at which neighboring utilities were operating their wells and
climatic conditions. If extractions were periodic, as in response to drought or delivery
reductions, extractions of 1,500 AFA are possible provided this use is short-lived (one year
every three or so years) and the basin is allowed to recover after this use.
These estimates were based on the best available data and on general knowledge of
groundwater basin behavior. However, the data was limited, as the basin has not been
actively pumped since 1963. When more information becomes available both from
developing the City’s wells for emergency use and from data collected from the SCVWD’s
monitoring well, these estimates will be re-examined.
The level of well use described above is not expected to result in reinitiation of subsidence
or seawater intrusion or the movement of contaminate plumes for the following reasons:
• Reinitiation of significant subsidence would require the dewatering of sediments not
dewatered as part of the water level declines of the last century. This would require
water level declines of more than 140 feet. As proposed the operation of the wells
would result in short term water level declines of between 20 and 30 feet, and
dewatering of previously dewatered and compacted sediments.
• The year-to-year 500 AFA extraction is intended to not lower groundwater levels
substantially, which would preserve the natural groundwater flow direction and
prevent saltwater intrusion. The periodic 1,500 AFA well use described above would
result in transient occurrence of water levels below sea-level. While water level below
sea-level will reverse the seaward gradient, the slow travel time of groundwater
provides a buffer from seawater intrusion for transient use.
• Operation of the wells would result in temporary disruption of natural flow directions
and could effect movement of contaminate plumes. However, no known contaminate
plumes exist proximate to the existing or proposed wells sites.
December 1, 2015
Save Palo Alto’s Groundwater requests the Policy and Services Committee to recommend the following for Council approval:
Institute an immediate moratorium on the issuing of dewatering permits for residential basements
until:
1.State mandated drought restrictions are lifted and
2. The City prioritizes engaging a consultant, preferably with knowledge of the local
aquifers to create a Groundwater Management Plan for Palo Alto
3.This Groundwater Management Plan should be incorporated Palo Alto’s Urban WaterManagement Plan, the next update which is due in July, 2016, and if practical,
coordinated with efforts in San Mateo County as the San Francisquito Creek Sub-basin is
shared between counties.
Specific concerns to be addressed in the Groundwater Plan: a. Create and implement a sustainable groundwater budget for Palo Alto taking into
account that this is a shared resource with neighboring cities and other entities.
b. Consider the prospect of climate change including possible periods of extended
drought and exceptional rains and that rising sea levels might led to greater possibility
of saltwater intrusion. c.Integrate groundwater management policies to Palo Alto's Sustainability goals.
d.Protection of water levels in both the deep and surface components of the aquifer
e.Integrate groundwater management policies to Palo Alto's Sustainability goals.
Additionally, the Groundwater Management Plan needs to be considered in the update to Palo Alto’s Comprehensive Plan, specifically N-18 and other applicable policies.
If under Palo Alto's Groundwater Management Plan the water budget allows for dewatering,
then:
1. Groundwater Pumping Allocations and Pricing
a.Priority for dewatering should be given to public projects, e.g. the Public Safety
Buildings
b. Normal water rates should be charged for this water, and the water should be priced at
or above replacement costs to the Cityc. Meter water to ensure accurate charges and to provide reliable data for the water
budget
d. Limit the issuance of dewatering permits to ensure that cumulative dewatering is
within the groundwater budget
2.Best practices and zero-waste policies
Adopt best practices and zero-waste policies for groundwater
Attachment B: Correspondence
a.The City will institute appropriate actions and policies to preserve a healthy
groundwater level and flows with costs paid by the developing party, including
i. requiring building practices and techniques that minimize dewatering, such as
shallower pumping depths, shorter pumping periods, or methods that do notrequire dewatering
ii.re-use of pumped water for (neighborhood) irrigation replacing use of potable
water for irrigation
iii.re-injection of the groundwater to the aquifer, preferably nearby
iv.Explicit consideration should be given to the cumulative effects ofdewatering at multiple sites in the same geographical area and require site-specific dewatering plans that minimizes the cumulative impacts on the
nearby properties, including requiring coordinated dewatering of such sites
when appropriate.
b.The City will create enforceable City policies and collect meaningful penalties whenpolicies are violatedc. Establish a roadmap to achieve “Zero Dewatering” waste within 5 years.
3. Zoning
Update zoning for basement construction by applying existing policy concepts to allunderground construction:a.individual review,
b.revised underground set back restrictions, including excavation,
c.depth and volume restrictions,
d. approved drainage requirements, specifically enhanced storm water collection andmitigation of the local impacts of a basement on groundwater flows,e.include basements, lightwells and below-grade construction and walls in FAR and
SAR regulations.
4.Local Impacts of DewateringThe City will require a determination of impacts of groundwater pumping on nearbybuildings, infrastructure and trees or landscaping
a.Applicants would determine and monitor the approximate extent of the temporary
groundwater zone of depression caused by pumping
b.Data will be readily available to the public online and of suitable quality to provide abasis for both understanding the aquifer and soils and to provide documentation in theevent of property damages
5. Storm Water Handling and Aquifer Recharge
Applicants will minimize and mitigate the impacts and costs of basements on the City’sstorm water handling and maximize local aquifer recharge capabilities.
6. Avoidance of multi-year adverse impacts
An qualified consulting firm will review Palo Alto's Water Budget every 2 years. Other than
for emergency purposes, whenever water outflows exceed inflows an immediate moratoriumon issuing dewatering permits will occur.
1
MEMORANDUM
TO: UTILITIES ADVISORY COMMISSION
FROM: UTILITIES DEPARTMENT
DATE: FEBRUARY 13, 2013
SUBJECT: Utilities Advisory Commission Review and Discussion of the 2013 Preliminary
Assessment of Water Resource Alternatives
RECOMMENDATION
Staff requests that the Utilities Advisory Commission discuss the Preliminary Assessment of
Water Resources Alternatives and the proposed next steps in the update of the Water
Integrated Resource Plan (WIRP). No action is required.
EXECUTIVE SUMMARY
An Integrated Resource Plan provides a detailed evaluation of current and potential resources
and policies and provides a blueprint to guide resource procurement and optimization for the
future. The City completed its first Water Integrated Resource Plan (WIRP) in 1993, and
updated the WIRP in 2003. Almost ten years have passed since the last WIRP, and it is time for
an update to ensure policies and guidelines are consistent with community preferences and the
changes that have occurred to the City of Palo Alto Water Utility. The WIRP update will include
several phases, starting with the attached Preliminary Assessment of Water Resource
Alternatives. The Preliminary Assessment describes each potential water resource alternative
available to the City using information currently available. The next phase will be a more
detailed analysis of various supply portfolio alternatives.
Staff is seeking feedback from the UAC on the proposed alternatives identified for further
review in the next phase.
BACKGROUND
The City prepared its first Water Integrated Resource Plan (WIRP) in 1993 when the City was
faced with a decision to participate in a regional recycled water expansion program. The 1993
WIRP assessed the costs and benefits of the recycled water project compared to other supply
alternatives, and ultimately concluded that recycled water was not cost effective relative to
existing supply.
In 2003, the City updated the WIRP. The 2003 WIRP indicated that supplies from the San
Francisco Public Utilities Commission (SFPUC) were adequate during normal years, but
Submitted at Committee meeting by Peter Drekmeier
additional supplies were needed in dry years to avoid shortages. The key conclusions from the
2003 WIRP analysis were:
The City’s existing contractual entitlement with the SFPUC provides adequate supplies;
The cost to connect to the Santa Clara Valley Water District (SCVWD) treated water
pipeline was prohibitive;
Continuous use of groundwater is not recommended;
The City should continue to evaluate recycled water; and
Continue the current Demand Side Measure programs and explore additional measures.
In December 2003, Council adopted WIRP Guidelines (Attachment A) for the development of
new water resources and the preservation of existing supplies, which are summarized below:
1. Preserve and enhance SFPUC supplies
2. Continue to advocate for an interconnection between SFPUC and SCVWD
3. Participate on the development of cost effective regional recycled water programs
4. Scope water conservation programs to comply with Best Management Practices (BMPs)
5. Maintain emergency water conservation measures to be activated in case of droughts
6. Retain groundwater supply options in case of changed future conditions
7. Survey community to determine its preferences regarding the best water resource
portfolio
2003 WIRP Guideline Summary Review
A summary of the current situation with respect to each of the 2003 WIRP Guidelines is
provided below.
Guideline #1 - Preserve and enhance SFPUC Supplies. This guideline had objectives including
that: a) the SFPUC regional water system be rebuilt; b) the cost of improvements is fairly
allocated; c) future water needs can be met; d) there are adequate supplies during drought; e)
the community prepare for potential water outages; f) the City implement cost effective water
conservation activities; g) water received must meet drinking water standards; h) the Master
Contract is properly implemented and a new contract is in place prior to 2009; and i) there is
ongoing support of efforts to protect health, safety and economic well-being of the water
customers and community.
The guideline was critical when the 2003 WIRP was completed since the SFPUC had not yet
adopted its Water System Improvement Program (WSIP) and the City’s contract with SFPUC
would expire in June 2009. In May 2008, the SFPUC adopted the WSIP and since then has been
earnestly implementing the rebuild of the regional system. In June 2009, a new Water Supply
Agreement was executed with San Francisco that resolved such issues as fair cost allocation,
drought supply allocation, and water quality assurances. In addition, the City Council adopted
the 2010 Urban Water Management Plan (UWMP) that establishes goals for water efficiency
resources (Staff Report #1688).
Guideline #2 - Advocate for an interconnection between the SFPUC and the SCVWD. In 2003
the SCVWD evaluated extending its treated water pipeline to serve Palo Alto and other north
county water retailers. During SCVWD’s preparation of the Water Supply and Infrastructure
Master Plan in 2012, staff again requested the SCVWD analyze a pipeline extension and
reliability interconnection with the SFPUC system. The SCVWD declined to evaluate an
extension in the plan, but indicated it may be considered in a future infrastructure reliability
master plan.
Guideline #3 – Actively participate in development of cost effective regional recycled water
plans: In 2006, the City completed a Recycled Water market Survey Report to determine
potential customers within the City, evaluate potential pipeline alignments, and provide
preliminary cost estimates. In 2008, the City completed a Recycled Water Facility Plan, which
identified a preferred pipeline alignment and prepared costs estimates for the preferred
project. In 2010, the City of Mountain View and the Regional Water Quality Control Plant
(RWQCP) completed a new recycled water pipeline to serve customers in the Mountain View
area. Since 2010, the City has developed a Mandatory Use Ordinance, a Salinity Reduction
Policy (CMR 121:10), is preparing environmental documents for the Palo Alto project, and has
been actively pursuing grant and low interest loan opportunities. Most recently, the RWQCP
completed a Long Range Facilities Plan (Staff Report #2914), which includes an assessment of
the current and future recycled water program and identifies program needs.
Guideline #4 – Focus Water DSM Programs to comply with BMPs: The City is a signatory to the
California Urban Water Conservation Council’s Memorandum of Understanding (MOU)
regarding urban water conservation. The City strives to implement programs that meet or
exceed the current BMPs as directed in the MOU and the City’s 2010 UWMP contains
aggressive water efficiency goals.
Guideline #5 - Maintain Emergency Conservation Measures to be activated in case of
droughts: The 2010 UWMP contains the actions and measures that will be implemented in
response to a drought.
Guideline #6 – Retain Groundwater Supply options in case of changed future conditions: The
City is currently developing the Emergency Water Supply and Storage Project. Although the
primary purpose of the project is to provide emergency water supplies during a catastrophic
interruption of SFPUC service, it includes the capability for further retrofits to some or all of the
new and refurbished wells for normal year use. However, the project’s Environmental Impact
Report (EIR) includes a mitigation measure limiting groundwater pumping to a maximum of
1500 AFY during a drought. The SCVWD, in its role as the groundwater steward for Santa Clara
County, recently completed an update to its Groundwater Management Plan. As part of the
process, staff requested additional analysis on the groundwater basin in the Palo Alto area.
This additional information may assist the City’s effort to modify the 1500 AFY limitation, if
there is an interest in doing so.
Guideline 7 – Survey Community to determine its preference regarding the best water
resource portfolio. In June 2004, staff presented the results of the community survey to the
UAC. The survey polled the community on the use of groundwater during a drought, and the
results indicated water quality issues were a primary concern. The report recommended the
City await the completion of the Emergency Water Supply and Storage project, and then
proceed with an evaluation of using groundwater as a supplemental source during a drought.
DISCUSSION
It has been almost a decade since completion of the last WIRP. Several key milestones have
occurred since then, and the water utility landscape continues to evolve in response to
legislation, the regulatory environment, and community preferences. The changes since the
2003 WIRP are driving the need to re-evaluate existing conditions to determine if adjustments
are needed.
2013 WIRP Update
The 2013 WIRP update will review and make necessary adjustments to the existing WIRP
guidelines so they are consistent with existing policies and reflect community preferences. The
completion of the Preliminary Assessment (Attachment B) is the first step in the development
of the 2013 WIRP.
The Preliminary Assessment provides a general evaluation of current resources and potential
future water resource alternatives based on the best available information. In some cases, the
evaluation of the resource option is based on consultant reports and analysis that was
performed over 10 years ago. Staff has refreshed the analysis to provide a current
representation as best as possible.
The potential water resources described in the Preliminary Assessment include:
1. Water from the SFPUC
2. Groundwater
3. Treated Water from the SCVWD
4. Recycled Water
5. Demand-Side Management
6. Sale of the City’s Individual Supply Guarantee
Water resources that were evaluated in the 2003 WIRP process, but are not included in this
Preliminary Assessment, include desalination, small scale groundwater wells for irrigation, and
treated contaminated groundwater.
One of the major changes since the 2003 WIRP is that the cost of SFPUC water has increased
significantly and has become much more expensive than water from the SCVWD as shown in
Figure 1 below.
Figure 1: Actual and Forecast Cost* of SFPUC and SCVWD Water Supplies
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
$/
A
c
r
e
-Fo
o
t
Fiscal Year
SFPUC vs. SCVWD
SCVWD - Groundwater Rate
SCVWD Treated Water rate
SFPUC Treated Water Rate
ForecastActual
* The bars for the SCVWD costs show a higher cost scenario that includes higher CIP spending.
Given the current and projected costs of water from the SFPUC and SCVWD, a rough estimate
of the total annual costs can be calculated if all of the City’s potable water supplies came from
either the SFPUC, SCVWD treated water, or groundwater. Table 1 below shows the estimated
annual cost in 2013, 2015, and 2020 for those three sources.
Table 1: Estimated Cost of Water Supply Alternatives
FY 2013 FY 2015 FY 2020
Water needs (AF/year) 13,500 14,243 14,971
Unit Cost ($/AF)
SFPUC supplies $1,259 $1,594 $2,134
SCVWD treated water $725-905 $850-1180 $1185-1695
Groundwater $625-805 $750-1080 $1085-1595
Annual Cost ($million) with:
100% SFPUC supplies $17.00 $22.70 $31.95
100% SCVWD treated
water $9.7-12.21 $12.1-16.8 $17.74-25.3
100% Groundwater (1) $9.7-12.21 $12.1-16.8 $17.74-25.3
(1) Cost includes O&M cost of $100/AF for operating the City’s wells
As shown in Table 1, there are potentially significant cost savings if the City discontinued using
water from the SFPUC and replaced it with groundwater or SCVWD treated water. However,
there are also water quality impacts that the community will need to determine are acceptable.
In addition, since the groundwater may not meet secondary drinking water quality standards,
there may be additional costs for treatment that are not included in these cost estimates.
Issues with Current Water Supplies
Besides the increasing cost of supplies from the SFPUC, the City’s current water supply is
vulnerable to water supply shortages in dry years. The current plans for dealing with these
shortages are to request, and provide incentives for, customers to reduce water usage. In
addition, groundwater is available as a supplemental supply in droughts. The new well planned
at El Camino Park can be blended with SFPUC supplies in the new reservoir prior to introduction
to the City’s distribution system to ensure that the water meets all water quality standards.
Presently, the City can use 1,500 acre-feet/year (AFY), or about 12% of the City’s current annual
usage, of groundwater.
Water Supply Options to Further Evaluate
Based on the Preliminary Assessment, staff has identified several water supply portfolio options
that merit further evaluation. This evaluation may involve additional analysis and/or consultant
assistance to provide more meaningful data for the various supply options to be properly
characterized and evaluated. Before a recommendation can be developed, several issues
require additional study and evaluation. These relate to the use of groundwater, SCVWD
treated water, recycled water, and the sale of the City’s unused ISG to SFPUC supplies. The
issues for each of these resource options that need more in-depth evaluation are described
below.
1. Groundwater – The 1,500 AFY mitigation measure limitation on the use of groundwater
reduces the City’s flexibility for using groundwater in droughts and in normal years. Staff
plans to pursue modification of that restriction. This may require additional groundwater
modeling and possibly an updated environmental review process. Depending on the
amount of groundwater the City would seek to use, the supporting analysis could require
intensive groundwater modeling and coordination with SCVWD, neighboring agencies and
other stakeholders.
2. SCVWD treated water – Since the City has no current connection to SCVWD’s treated water
system, using treated water would require an extension of the SCVWD’s West Pipeline to an
interconnection point at Page Mill Road. An evaluation of this option may require an
updated West Pipeline extension study similar to the one done in 2003. The study would
evaluate the costs and cost allocation scenarios for the interconnection. Implementation of
this alternative would require the City to execute several new contracts and revise the
existing contract with the SFPUC. Staff anticipates the SCVWD will perform the necessary
environmental reviews for a West Pipeline extension.
3. Recycled water – Recycled water is a unique, non-potable supply source that would
augment the portfolio with a locally controlled, diverse supply capable of providing dual
benefits from a water and wastewater perspective. As discussed in the Preliminary
Assessment, the evaluation of a recycled water extension to serve the Stanford Research
Park is underway and a recommendation on a future recycled water project depends on
securing an outside funding source. Following completion of the environmental document,
staff will prepare a financial feasibility report and make recommendations on an expansion
of the recycled water distribution system.
4. Sale of the City’s unused Individual Supply Guarantee (ISG) to SFPUC supplies – Water
transfers can be complicated and require time to structure. Considering recent events that
have provided indicative pricing for a potential transaction, staff recommends the City begin
the evaluation of a transfer of the City’s ISG. While potential revenues are a major factor in
the recommendation to move forward, staff has been monitoring the differential between
water consumption and the City’s ISG for some time. In light of the historical and projected
ISG surplus, a sale of a small portion of the City’s ISG may be in the best interest of the
community. Proceeds from a sale could reduce water rates or provide funds for increased
conservation programs or the recycled water project.
The evaluation of recycled water and a sale of some of the City’s ISG are proceeding
independently. Examples of water supply portfolios that staff proposes to evaluate in more
detail are shown in Table 2.
Table 2: Water Supply Portfolios to Evaluate
Portfolio SFPUC supplies SCVWD Treated
Water Supplies
Groundwater
Status Quo 100% of normal
year needs
None Up to 1,500 AFY for supplemental
supply in droughts
Increased
Groundwater
50% of normal
year needs
None 50% of normal year needs
Treated Water
Usage
50% of normal
year needs
50% of normal
year needs
Up to 1,500 AFY for supplemental
supply in droughts
Only Treated Water
and Groundwater
None 50% of normal
year needs
50% of normal year needs
NEXT STEPS
Preparation of the 2013 WIRP will proceed through FY 2013, and will likely extend into FY 2014
depending on the level of additional studies and outside consultant assistance that is
appropriate. Staff will return to the UAC with more detailed information and supporting
analysis for the different water supply portfolio options. Staff will also evaluate a potential ISG
sale and return to the UAC with a recommendation on moving forward with a transaction.
Finally, staff will continue ongoing efforts to complete an extension of the recycled water
system to serve customers in the Stanford Research Park and return to the UAC with a financing
plan once there is a reasonable expectation that supplemental outside funding can be secured.
Following selection of preferred options based on the additional evaluations in the next phase,
staff will prepare a Draft Water Integrated Resource Plan and propose modifications to the
WIRP Guidelines.
ENVIRONMENTAL REVIEW
The UAC's review and discussion of the Preliminary Assessment of Water Resource Alternatives
does not meet the California Environmental Quality Act's definition of a "project" under Public
Resources Code Section 21065, thus no environmental review is required.
ATTACHMENTS
A. 2003 Water Integrated Resource Plan Guidelines
B. 2013 Preliminary Assessment of Water Resource Alternatives
PREPARED BY:
REVIEWED BY:
DEPARTMENT HEAD:
NICOLAS PROCOS, Senior Resource Planner~ lf E RATOIYE, ,.,;~'°' o;cocto<, "''°"'~ Mooo,omoo'
VALERI~
WIRP Guidelines Adopted by Resolution by the City Council on December 8, 2003 [CMR:547:03]
Guideline 1 – Preserve and enhance SFPUC supplies: With respect to the City of Palo Alto
Utilities’ (CPAU’s) primary water supply source, the San Francisco Public Utilities Commission
(SFPUC), continue to actively participate in the Bay Area Water Supply and Conservation
Agency (BAWSCA) to assist in achieving BAWSCA’s stated goal: “A reliable supply of water, with high quality, and at a fair price.” Objectives in support of that overall goal include:
A. That the regional water system gets rebuilt cost-effectively and that BAWSCA
monitor implementation of AB 1823 – San Francisco should safeguard the water
system against damage from earthquakes and other foreseeable hazards. BAWSCA
will monitor progress on the system repairs and on completing the requirements of the legislation that the BAWSCA agencies supported to oblige San Francisco to
repair and rebuild the regional system.
B. That the cost of improvements is fairly allocated – San Francisco should commit to
maintaining cost-based pricing, with the costs of the wholesale water system shared
between the City and its wholesale customers based on their proportionate share. C. That future water needs can be met – San Francisco must evaluate the ability of the
regional system to meet future supply and capacity requirements and must use the
BAWSCA agencies’ long-term water demand forecasts as the basis for regional water
demand projections.
D. That there are adequate supplies during droughts – San Francisco should arrange back-up supplies for dry years and should “drought proof” the entire service area, not
just San Francisco itself. If rationing becomes necessary, San Francisco should use a
system that allocates available water between San Francisco and wholesale customers
in a way that (1) is fair and (2) avoids penalizing long-term conservation efforts
and/or development of alternative supplies, such as recycled water. E. That communities prepare for potential water outages – San Francisco should
coordinate with the BAWSCA agencies to develop a crisis management plan.
F. That agencies implement cost-effective water conservation activities – San Francisco
should provide agencies enough information so that they can prepare for possible
outages, including the provision of conservation programs for their communities. BAWSCA can act as coordinator for these programs to improve the cost-
effectiveness of agencies offering such programs.
G. That water received must meet drinking water standards – San Francisco should
continue to protect the purity of Hetch Hetchy water and commit to provide its
wholesale customers with water that meets EPA and California drinking water standards.
H. That the Master Contract is properly implemented and a new Master Contract is in
place prior to 2009 – San Francisco should commit to maintaining cost-based pricing,
with the costs of the wholesale water system shared between the City and its
wholesale customers based on their proportionate share. I. That there is ongoing support of efforts to protect health, safety and economic well
being of the water customers and communities – BAWSCA should maintain the
support of the many allies who supported the legislative effort to ensure San
Francisco repairs, rebuilds, and maintains the regional system.
Guideline 2 – Advocate for an interconnection between SFPUC and the District: Work with
the Santa Clara Valley Water District (District) and the SFPUC to pursue the extension of the
District’s West Pipeline to an interconnection with the SFPUC Bay Division Pipelines 3&4.
Continue to re-evaluate the attractiveness of a connection to an extension of the District’s West Pipeline.
Guideline 3 – Actively participate in development of cost-effective regional recycled water plans: Re-initiate discussions with the owners of the Palo Alto Regional Water Quality Control
Plant (PARWQCP) on recycled water development. In concert with the PARWQCP owners, conduct a new feasibility study for recycled water development. Since the feasibility of a recycled water system depends upon sufficient end-user interest, determine how much water
Stanford and the Stanford Research Park would take.
Guideline 4 – Focus water DSM programs to comply with BMPs: Continue implementation of water efficiency programs with the primary focus to achieve compliance with the Best Management Practices (BMPs) promoted by the California Urban Water Conservation Coalition.
Guideline 5 – Maintain emergency water conservation measures to be activated in case of droughts: Review, retain, and prioritize CPAU’s emergency water conservation measures that would be put into place in a drought time emergency. Guideline 6 – Retain groundwater supply options in case of changed future conditions:
Using groundwater on a continuous basis does not appear to be attractive at this time due to the
availability of adequate, high quality supplies from the SFPUC in normal years. However, SFPUC supplies are not adequate in drought years and circumstances could change in the future such that groundwater supplies could become an attractive, cost-effective option. Examples of
changing circumstances could be that the amount of water available to CPAU from the SFPUC
for the long-term is reduced. This could occur if regulations or legislation require additional
water to be made available to the Tuolumne River fisheries. In addition, in the future allocations or entitlements to SFPUC water may be developed. If those allocations are based on the dry-
year yield of the system, allocations to all the users of the system, including CPAU, could be
well below their current and projected future needs. CPAU should retain the option of using
groundwater in amounts that would not result in land surface subsidence, saltwater intrusion, or
migration of contaminated plumes.
Guideline 7 – Survey community to determine its preferences regarding the best water resource portfolio: Seek feedback from all classes of water customers on the question of
whether to use groundwater during drought to improve drought year supply reliability. At the
same time, seek feedback on the appropriate level of water treatment for groundwater if it were to be used in droughts. Survey all classes of water customers to determine their preferences as to
the appropriate balance between cost, quality, reliability, and environmental impact.
PRELIMINARY ASSESSMENT
OF WATER RESOURCE
ALTERNATIVES
February 2013
i
2013 Preliminary Assessment
Table of Contents
List of Figures ___________________________________________________________ iii
List of Tables ___________________________________________________________ iii
List of Acronyms _________________________________________________________ iii
I. Introduction __________________________________________________________ 1
II. Background __________________________________________________________ 2
III. Water Supply History __________________________________________________ 3
IV. Water Use Projections _______________________________________________ 6
Urban Water Management Plan (UWMP) _________________________________________ 6
Water Conservation Bill of 2009 _________________________________________________ 7
Summary Water Resource Mix __________________________________________________ 7
V. Attributes Evaluated and Water Resource Alternatives Examined ______________ 8
Attributes Evaluated for each Water Resource Alternative ___________________________ 8
Water Resource Alternatives Examined __________________________________________ 9
VI. Water from the SFPUC ______________________________________________ 10
Availability _________________________________________________________________ 10
Cost ______________________________________________________________________ 12
Water Quality ______________________________________________________________ 13
Long Term Reliability ________________________________________________________ 13
Emergency Robustness _______________________________________________________ 15
Environmental impacts _______________________________________________________ 16
Sensitivity to Regulations _____________________________________________________ 16
VII. Groundwater _____________________________________________________ 17
Availability _________________________________________________________________ 18
Cost ______________________________________________________________________ 20
Water Quality ______________________________________________________________ 21
Long Term Reliability ________________________________________________________ 24
Emergency Robustness _______________________________________________________ 24
Environmental impacts _______________________________________________________ 24
Sensitivity to Regulations _____________________________________________________ 24
VIII. SCVWD Treated Water ______________________________________________ 25
Availability _________________________________________________________________ 26
Cost ______________________________________________________________________ 26
Water Quality ______________________________________________________________ 28
Long Term Reliability ________________________________________________________ 28
Emergency Robustness _______________________________________________________ 28
Environmental Impacts _______________________________________________________ 30
ii
Sensitivity to Regulations _____________________________________________________ 30
IX. Recycled Water ______________________________________________________ 31
Availability _________________________________________________________________ 32
Cost ______________________________________________________________________ 35
Water Quality ______________________________________________________________ 36
Long Term Reliability ________________________________________________________ 37
Emergency Robustness _______________________________________________________ 37
Environmental Impacts _______________________________________________________ 37
Sensitivity to Regulations _____________________________________________________ 37
X. Demand‐Side Management ____________________________________________ 38
Availability _________________________________________________________________ 38
Cost ______________________________________________________________________ 40
Water Quality ______________________________________________________________ 40
Long Term Reliability ________________________________________________________ 41
Emergency Robustness _______________________________________________________ 41
Environmental Impacts _______________________________________________________ 41
Sensitivity to Regulations _____________________________________________________ 42
XI. Individual Supply Guarantee Sale ________________________________________ 42
Availability _________________________________________________________________ 42
Cost ______________________________________________________________________ 42
Water Quality ______________________________________________________________ 43
Long Term Reliability ________________________________________________________ 43
Emergency Robustness _______________________________________________________ 43
Environmental Impacts _______________________________________________________ 43
Sensitivity to Regulations _____________________________________________________ 44
iii
List of Figures
Figure 1: Historic Water Use ........................................................................................................... 5
Figure 2: 2005 and 2010 UWMP Demand Forecast Projection Comparison ................................. 6
Figure 3: 20% by 2020 Compliance Forecast .................................................................................. 7
Figure 4: Summary Water Resource Composition .......................................................................... 8
Figure 5: SFPUC Actual and Projected Cost of Water ................................................................... 12
Figure 6: Historic Water Shortages at Maximum Demand Level (265 MGD) ............................... 15
Figure 7: Map of SFPUC Regional Water System .......................................................................... 16
Figure 8: Projected SFPUC and SCVWD Water Rates ................................................................... 21
Figure 9: West Pipeline Extension Map ........................................................................................ 26
Figure 10: Proposed Recycled Water Project ............................................................................... 32
Figure 11: Palo Alto Existing Recycled Water Uses for FY 2004‐FY 2012 .................................... 34
Figure 12: Water Conservation Savings Goals .............................................................................. 39
List of Tables
Table 1: City Of Palo Alto Water Shortage Allocation .................................................................. 11
Table 2: Dry Year Shortfall under different demand scenarios .................................................... 14
Table 3: Projected Well Capacities ............................................................................................... 20
Table 4: Water Quality Parameters for Various Water Sources ................................................... 22
Table 5: Well Treatment Alternative Preliminary Cost Analysis ................................................... 23
Table 6: SCVWD Treated Water Connection Summary Costs ...................................................... 27
Table 7: Recycled Water Gross Cost Estimate .............................................................................. 35
Table 8: Water Savings vs. Goals .................................................................................................. 39
Table 9: Conservation Program Costs ........................................................................................... 40
List of Acronyms
AFY Acre Feet per Year
BAWSCA Bay Area Water Supply and Conservation Agency
BMP Best Management Practice
CDPH California Department of Public Health
CEQA California Environmental Quality Act
CUWCC California Urban Water Conservation Council
CVP Central Valley Project
DSM Demand Side Management
EIR Environmental Impact Report
ESA Endangered Species Act
FERC Federal Energy Regulatory Commission
iv
GWMP Groundwater Management Plan
ISA Interim Supply Allocation
ISG Individual Supply Guarantee
ISL Interim Supply Limitation
MGD Million gallons per day
MOU Memorandum of Understanding
NEPA National Environmental Policy Act
PEIR Program Environmental Impact Report
PPM Parts per Million
RWQCP Regional Water Quality Control Plant
SCVWD Santa Clara Valley Water District
SFPUC San Francisco Public Utilities Commission
SRF State Water Resources Control Board State Revolving Fund
SWP State Water Project
SWRCB State Water Resources Control Board
TDS Total Dissolved Solids
TRC Total Resource Cost
UAC Utilities Advisory Commission
UWMP Urban Water Management Plan
WIRP Water Integrated Resource Plan
WSA Water Supply Agreement
WSIP Water System Improvement Program
Page 1
I. Introduction
Preparation of a Preliminary Assessment of Water Resource Alternatives is the first step
towards development of a Water Integrated Resource Plan (WIRP). The Preliminary
Assessment collects the available information and data about all water resource alternatives
available to the City of Palo Alto. The following are a summary of the main drivers for updating
the WIRP at this time.
a) Cost Increases – The San Francisco Public Utilities Commission (SFPUC) is midway through
the $4.6 billion Water System Improvement Program (WISP), which includes an upgrade of
the regional water system. As a result of the WSIP, the cost of SFPUC water has risen
dramatically and will continue to do so. With the increase in costs, other alternatives are
increasingly competitive with SFPUC supplies.
b) SFPUC Wholesale Water Charge – The SFPUC currently collects the wholesale revenue
requirement primarily through a volumetric water rate. The SFPUC may propose changes
to the current wholesale rate structure that include a fixed charge based on the Individual
Supply Guarantee. Since the City has a relatively high Individual Supply Guarantee, this
could change the City’s cost dramatically and make other alternatives more cost‐effective.
c) Dry year need – The City has an Individual Supply Guarantee of 17.07 million gallons per
day (MGD) from the SFPUC system. The City has no foreseeable supply deficiency in
normal years, but SFPUC supplies are inadequate during dry years. A critical question to
address is the level of reliability the City will provide to residents and businesses and at
what cost.
d) Disposition of “Surplus” SFPUC Individual Supply Guarantee– The City currently uses
substantially less than its Individual Supply Guarantee. Considering long lead times to
execute water transfers, it may be the time for the City to proceed towards a sale of a
portion of the Individual Supply Guarantee. The sale could generate revenue for a variety
of options, including increased dry year reliability, conservation programs, a recycled water
project, or to reduce rates.
e) Alternative Supplies – The Santa Clara Valley Water District’s (SCVWD’s) groundwater and
treated water charges have historically been similar to the cost of SFPUC supplies. Over
the last few years, and for the foreseeable future, SCVWD water charges will be lower than
SFPUC charges, making groundwater or a connection to the SCVWD’s treated water system
potentially cost‐effective alternatives to SFPUC water.
f) Use of Palo Alto Groundwater System – The City has recently refurbished the five older
wells, developed two new wells and is completing another new well. One or more of the
Page 2
wells could be used to provide supplemental dry year supplies or as an alternative to
SFPUC supplies during normal years.
g) Legislative & Regulatory Risks – The City’s 2010 Urban Water Management Plan (UWMP)
incorporates recent and future legislative and regulatory requirements to provide a
comprehensive forward looking review of the water utility. A major new development is
Senate Bill 7x‐7 (2009), which requires a 20% reduction in per capita water use by 2020.
II. Background
The first WIRP was prepared largely because the City was faced with a decision to participate in
a regional recycled water program. This 1993 WIRP assessed the costs and benefits of a
recycled water project compared to other supply alternatives, and ultimately determined that
recycled water was not cost effective relative to existing supplies. In 1999, the City began
working on a new WIRP, and completed the effort with approval by the City Council of the
WIRP Guidelines in December 2003 (CMR 547:03). During the process to prepare the 2003
WIRP, several studies were conducted to inform the effort:
1. Water, Wells, Regional Storage, and Distribution System Study, 1999, Carollo Engineers –
This study identified system improvements to the distribution system to meet water
demands and fire flows following a catastrophic interruption of service on the SFPUC
system. Among the recommendations was to refurbish the 5 existing wells and construct
three new wells and a new water storage tank.
2. Long Term Water Supply Study, 2000, Carollo Engineers – The report examined the issues
and costs of using new or rehabilitated wells as active sources of supply. The alternatives
examined in the report included: (1) Using the wells for active supply either on a long term
basis or during droughts; (2) using groundwater for irrigation; and (3) connecting to the
SCVWD treated water pipeline.
3. Groundwater Supply Feasibility Study, 2002, Carollo Engineers – The report evaluated
whether operating one or two of the City’s water wells as active supplies would cause
significant decrease in groundwater levels or deterioration in groundwater quality”.
4. Santa Clara Valley Water District’s West Pipeline Extension Conceptual Evaluation Final
Report, 2003, SCVWD. – The report evaluated an extension of the existing SCVWD West
Pipeline to enable an interconnection of the Palo Alto and SCVWD systems at Page Mill
turnout.
The 2003 WIRP indicated that SFPUC supplies were adequate during normal years, but
additional supplies were needed in dry years to avoid shortages. Since SFPUC supplies were
adequate in normal years, the following conclusions were drawn:
Page 3
1. The City’s existing Individual Supply Guarantee provides adequate supplies;
2. The cost to connect to the SCVWD treated water pipeline was prohibitive;
3. Continuous use of groundwater is not recommended;
4. The City should continue to evaluate recycled water;
5. Continue the current Demand Side Management programs and explore additional
measures; and
6. Additional supplies are needed in a drought.
Following approval of the 2003 WIRP, staff surveyed residential customers to gain a sense of
community preferences on the use of groundwater during a drought. The survey asked
respondents to rank several options for water supply during a drought: (A) blend groundwater
with existing SFPUC supplies; (B) use no groundwater; and (C) treat groundwater at the well
location prior to introduction to the distribution system.
Survey respondents generally preferred Options B (no groundwater) and C (treat groundwater),
but Option A (blend groundwater) was not soundly rejected. The results of the survey were
presented to the UAC in June 2004. Based on the results staff made the following
recommendations:
1. Do not install advanced treatment systems for the groundwater at this time. This option
is expensive, both in terms of capital and operating costs.
2. Blending at an SFPUC turnout is the best way to use ground water as a supplemental
drought time supply while maintaining good water quality.
3. Staff should await the conclusion of the environmental review process before
proceeding with any site selections for wells to be used in dry years.
4. Actively participate in the development of long term supply plans with the Bay Area
Water Supply and Conservation Agency (BAWSCA) and/or SCVWD.
5. Continue efforts identified in the Council approved WIRP guidelines:
a. Evaluate a range of demand side management options to reduce long term
water demands.
b. Evaluate feasibility of expanding recycled water.
c. Maintain emergency water conservation measures to be activities in case of
droughts.
III. Water Supply History
The water utility was established on May 9, 1896, two years after the City was incorporated.
Local water companies were purchased at that time with a $40,000 bond approved by the
voters of the 750‐person community. These private water companies operated one or more
shallow wells to serve the nearby residents. The city grew and the well system expanded until
nine (9) wells were in operation by 1932.
Page 4
In December 1937, the City signed a 20‐year contract with the City and County of San Francisco
for water deliveries from the newly constructed pipeline bringing Hetch Hetchy water from
Yosemite to the Bay Area. Water deliveries from San Francisco commenced in 1938 and well
production declined to less than half of the total citywide water demand.
A 1950 engineering report noted, "The capricious alternation of well waters and the [San
Francisco] water...has made satisfactory service to the average consumer practically
impossible." Groundwater production increased in the 1950s leading to lower groundwater
tables and increasing water quality concerns.
In 1962, a survey of water softening costs to City customers determined that the City should
purchase 100% of its water supply needs from the San Francisco. A 20‐year contract was signed
with San Francisco and the City’s wells were placed in a standby condition. Since 1962 (except
for some very short periods) the City’s entire potable water has come from San Francisco’s
Hetch Hetchy regional water system administered by the SFPUC.
In 1974, several wholesale customers joined Palo Alto and filed a lawsuit against the San
Francisco in protest of an increase in water rates that was higher for wholesale customers than
it was for direct retail customers. In 1984, settlement negotiations resulted in the “Settlement
Agreement and Master Water Sales Contract between the City and County of San Francisco and
Certain Suburban Purchasers in San Mateo, Santa Clara and Alameda Counties”. The 25‐year
agreement was approved in 1984. The 1984 agreement included the creation of a “Supply
Assurance” equal to 184 million gallons of water per day (MGD) for the benefit of the wholesale
customers.1 The agreement included a mechanism to allocate the 184 Supply Assurance
between the wholesale agencies. The City’s allocation, or Individual Supply Guarantee (ISG), is
17.07 MGD. Each agency’s ISG is perpetual in nature and survives termination or expiration of
the water supply contract with San Francisco.
1 The Supply Assurance is expressed as an annual average and does not constitute an obligation on the part of the
SFPUC to meet daily or hourly peak demands.
Page 5
In 2009, a new 25‐year Water Supply Agreement (WSA) was executed between San Francisco
and the City. The City’s historical water use and supply sources are illustrated in Figure 1.
Figure 1: Historic Water Use
Page 6
IV. Water Use Projections
The City of Palo Alto Utilities (CPAU) regularly prepares water supply and demand forecasts to
prepare financial forecasts, to meet regulatory requirements, or as part of ongoing regional
planning efforts. Like many water agencies in California, the City has experienced a significant
drop in water use since 2006, which is largely attributable to weather, water conservation, and
the recent economic recession.
Urban Water Management Plan (UWMP)
The UWMP is submitted to the Department of Water Resources every five years, and City
Council approved the most recent 2010 UWMP in June 2011 (Staff Report 1688)2. Water
demands forecast for the 2010 UWMP are shown in Figure 2 below. For comparison purposes,
the forecast from the 2005 UWMP is also included in Figure 2. The water use projection results
are revealing in that the City, along with most water agencies in California, did not anticipate
the dramatic drop in water demand from 2007 to 2009. Potable water demands from 2009 to
the present appear to have leveled off and have begun to trend upwards again, albeit slowly,
and it remains to be seen if water demands will follow the increase forecasted in the 2010
UWMP.
Figure 2: 2005 and 2010 UWMP Demand Forecast Projection Comparison
0
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1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030
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Water from San Francisco
2010 UWMP Forecast
2005 UWMP Forecast
Individual Supply Guarantee
Actual Forecast
2 Typically, UWMPs are due December 31 of years ending in 0 and 5. However, a six‐month extension
was granted to allow suppliers to comply with new legislation (Senate Bill X7‐7).
Page 7
Water Conservation Bill of 2009
The City is subject to ongoing changes in the regulatory and legislative environment, though
few are as explicit as SB X7‐7, the Water Conservation Bill of 2009. SB X7‐7 was enacted in
November 2009 and requires water suppliers to reduce the average per capita daily water
consumption in their service territories 20% by 2020. To monitor the progress towards
achieving the 20% by 2020 target, the bill also requires urban water retail providers to reduce
per capita water consumption 10% by 2015. Figure 3 illustrates the projected 2015 and 2020
state‐mandated compliance targets and provides preliminary information on the City’s need for
future action to meet SB7x‐7 requirements.
Figure 3: 20% by 2020 Compliance Forecast
100
125
150
175
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2015 Target = 200.6
SB7 Baseline
2020 Target = 178.6
Figure 3 indicates that the City is on track to meet both the 2015 and 2020 state‐mandated
compliance targets.
Summary Water Resource Mix
The 2010 UWMP provided detailed information on baseline water resources through 2030.
SFPUC supplies were assumed to remain the primary potable supply for the foreseeable future,
Page 8
but were not forecasted to increase dramatically over the 20‐year planning horizon. Recycled
water consumption was projected to continue at current levels and no expansion was assumed
in the 2010 UWMP. Finally, demand side management and conservation program penetration
and savings were projected to increase dramatically from the 2005 UWMP. A representation
of the future water resource mix is provided in Figure 4.
Figure 4: Summary Water Resource Composition
V. Attributes Evaluated and Water Resource Alternatives Examined
Attributes Evaluated for each Water Resource Alternative
In this section, each potential water resource option is evaluated to allow each alternative to be
compared to each other. The purpose of this evaluation is to provide the best available
information on each water resource alternative and to identify data deficiencies that need to
be addressed. The attributes evaluated for each alternative are listed below:
1. Availability – The quantity, timing, peak flow or capacity, and any expected changes
over time.
2. Cost – The capital and O&M costs of the proposed action (including system upgrades,
project lifetime, energy costs, chemicals, technical innovation, customer costs, etc.), the
manner which the cost is incurred (pay‐as‐you‐go, debt finance, etc.).
Page 9
3. Water Quality – All options must meet water quality regulations, but options may differ
in their relative water qualities (i.e. taste, odor, color, hardness, mineral content, trace
levels of contaminants, etc.).
4. Long Term Reliability – What is the reliability of the source under different conditions?
What future conditions could affect water deliveries?
5. Emergency Robustness – Will the resource perform under various scenarios, including
an interruption of SFPUC supplies?
6. Environmental impacts – Are there anticipated environmental impacts and what level
of environmental review is required?
7. Sensitivity to Regulations – Is the resource vulnerable or does it have strength in view
of existing or impending federal, state, or local regulations?
Water Resource Alternatives Examined
The water resource alternatives evaluated in this report include:
1. Water from the SFPUC
2. Groundwater
3. Treated Water from the SCVWD
4. Recycled Water
5. Demand‐Side Management
6. Sale of the City’s Individual Supply Guarantee
Water resources that were evaluated in the 2003 WIRP process, but are not included in this
Preliminary Assessment, include:
1. Desalination – BAWSCA is evaluating several desalination alternatives as part of recent
long range supply studies. When this effort is complete, this alternative can be
evaluated.
2. Small scale irrigation wells – The City is focusing its efforts on the capital program to
improve the municipal well system to meet the dual purpose of providing emergency
and supplemental potable supplies. Currently, individuals may drill their own wells
without City review or permits, but are subject to rules and restrictions of the Santa
Clara Valley Water District (SCVWD) and must obtain a permit from the SCVWD. The City
does have the option of using small wells for irrigation of large landscapes, such as for
City parks. However, the cost to maintain and operate small wells and locate a site for
such facilities is problematic.
3. Treated Contaminated Groundwater – There are several entities in the City that treat
contaminated groundwater and discharge the groundwater to the storm drain system
and, to a lesser extent, the sanitary sewer system. The primary purpose of these
facilities is to remediate contaminated groundwater with finite operations. The Santa
Clara County Oregon Expressway dewatering pumps are the exception, and they
discharge significant amounts of nuisance groundwater to the storm drain system to
Page 10
keep the underpass dry. The City evaluated the capture and conveyance of the Oregon
Expressway groundwater for irrigation purposes and determined the effort would
require significant conveyance and storage infrastructure investments that are not cost
effective.
VI. Water from the SFPUC
The City currently purchases 100% of its potable supplies from the SFPUC under the 2009
Water Supply Agreement (WSA). The WSA is administered for the City by the Bay Area Water
Supply and Conservation Agency (BAWSCA). BAWSCA represents the interests of 24 cities and
water districts and two private utilities that purchase wholesale water from the San Francisco
regional water system. These entities provide water to 1.7 million people, businesses and
community organizations in Alameda, Santa Clara and San Mateo counties. The City of Palo
Alto is a member of BAWSCA and has a City Council appointed representative on the BAWSCA
Board of Directors.
Availability
The City’s right to water from the SFPUC system is embodied in the 2009 WSA. The City’s
Individual Supply Guarantee (ISG) of 17.07 MGD is a perpetual right, but the delivery of water is
subject to interruption for reason of water shortage, drought, or emergency.
Normal Year SFPUC Supplies
While the City’s ISG is 17.07 MGD, the City’s water needs are currently only about 11.5 MGD.
The WSA includes an interim water delivery limitation3 from the SFPUC system of 265 MGD
until its expiration in 2018. The City’s share of the interim limitation, or its Interim Supply
Allocation (ISA), is 14.70 MGD. Based on the water demand forecast from the 2010 UWMP,
there is no foreseeable need for additional supply beyond the City’s Individual Supply
Guarantee, or the ISA.
Dry Year SFPUC Supplies
SFPUC’s WSIP includes a goal of no greater than a 20% system‐wide supply reduction on the
SFPUC system during a drought. The 2009 WSA includes a water shortage allocation plan to
share water from the regional system between the SFPUC retail and wholesale customers
during a shortage of up to 20% (Tier I plan). The wholesale customers further divided the
wholesale allocation based on a formula adopted by all the wholesale customers (Tier II plan).
The detail of the allocation methodology is included in the City’s 2010 UWMP (Section 7 –
Water Shortage Contingency Plan) and was approved by City Council in February 2011 (Staff
Report 1308). The Tier II formula expires in 2018, unless extended by mutual agreement of the
BAWSCA members. Table 1 summarizes the effect of the water shortage allocation formula on
3 This limitation applies to all users of the San Francisco regional water supply system, the City of San Francisco and
all the BAWSCA member agencies.
Page 11
Palo Alto during a 20% SFPUC system‐wide reduction under low demand and high demand
scenarios.4
Table 1: City Of Palo Alto Water Shortage Allocation
Palo Alto Allocation
(low demand)
Palo Alto Allocation
(High demand)
(a) Baseline Demand (MGD) 11.63 13.33
(b) Drought Allocation (MGD) 8.94 10.011
(c) Reduction from Baseline Demand (b‐a)
(MGD) ‐2.69 ‐3.32
(d) Percentage reduction from Baseline
Demand (c/a) ‐23.12% ‐24.90%
The results in Table 1 indicate that the City will experience a water supply deficit of 23‐25% in
the event of a 20% system‐wide water shortage on the SFPUC system.
4 In general, changes in Palo Alto demand patterns track many of the other BAWSCA members. However, the
ultimate allocation to each BAWSCA agency depends on many factors, including the water use of each agency
relative to each other. For these reasons, staff can only provide an approximation of the potential cutback.
Page 12
Cost
The City purchases 100% of its potable water supply from the SFPUC, with the current cost
structure composed of a volumetric charge and a small fixed monthly meter charge. With the
$4.6 billion WSIP well underway, the cost of SFPUC water has increased sharply. Recent region‐
wide water consumption declines have intensified the problem since the cost is spread over
fewer sales units. The historic and projected cost of SFPUC water is illustrated in Figure 5.
Figure 5: SFPUC Actual and Projected Cost of Water
0
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While the SFPUC charges wholesale customers based on how much water is used, the costs of
the SFPUC system are almost entirely fixed costs – in other words, even if usage drops the cost
to operate the system (O&M, debt service, etc.) remains essentially the same5.
The SFPUC water cost projections in Figure 5 assume that the current rate structure remains in
place. However, the WSA provides some flexibility for the SFPUC to adjust rate structures and
the SFPUC recently signaled an interest in exploring alternative rate structures6 including
increasing the fixed charge component and allocating charges based on the ISG, rather than
actual water usage. The City’s share of the costs paid by the BAWSCA agencies (the “Wholesale
Revenue Requirement”), steadily decreased from 8% in 1998 to 7.2% in 2010 as the City’s
proportional share of water purchases dropped relative to the other BAWSCA agencies. In
5 The SFPUC system is largely gravity fed, so little variable O&M is required for water deliveries. 6 SFPUC Comments, July 2012 BAWSCA Board of Director’s meeting
Page 13
recent years the City’s share of the Wholesale Revenue Requirement has increased slightly,
probably as a result of several SFPUC customers making economic decisions to reduce SFPUC
purchases to minimum amounts in favor of other, less costly supplies. The City’s ISG of 17.07
MGD is approximately 9.23% of the total BAWSCA agencies’ Supply Assurance of 184 MGD. If
collection of the Wholesale Revenue Requirement were to be based on each agency’s ISG, the
City could pay 20‐30% more for water annually, with little apparent increase in benefit.
Water Quality
SFPUC supplies are extremely high quality. See Table 4 which lists key water quality parameters
for SFPUC water, SCVWD treated water and groundwater. Water provided by the SFPUC is a
mix of Hetch Hetchy water and water from the East Bay and Peninsula reservoirs. In an average
year, Hetch Hetchy water makes up 85% of the mix. Due to maintenance requirements, the
SFPUC typically will shut down the Hetch Hetchy supply for a period during the low demand
winter months and draw from the local reservoirs. It is not unusual to experience temporary
water quality changes due to these events, though the water still meets all drinking water
quality standards.
Since completion of the 2003 WIRP, there were two noteworthy operational changes on the
SFPUC system that related to water quality: In 2004, the SFPUC starting using chloramine
instead of chlorine as the primary drinking water disinfectant. In 2005, San Francisco began
adding fluoride to the water supply. Up until then, the City introduced fluoride at the SFPUC
turnouts, but ceased to do so once the SFPUC began providing fluoridation from a centralized
facility7.
Long Term Reliability
Recent demand projections do not forecast a normal year supply deficiency, given the
perpetual nature of the City’s Individual Supply Guarantee. However there is one situation
where the City’s Individual Supply Guarantee could be reduced. Under the terms of the 1962
contract between it and San Francisco, the City of Hayward’s contractual entitlement from the
SFPUC system essentially equals its water demand. In theory, since the collective Supply
Assurance of the wholesale customers cannot exceed 184 MGD, if Hayward’s water usage
increases substantially, the other wholesale agencies could experience a proportional ISG
reduction to ensure the 184 MGD limit is not exceeded. The most recent water use projection
shows this will not be an issue until at least 2030, and it will proceed gradually in any event.
SFPUC’s level of service goal is to meet dry year delivery needs while limiting rationing to a
maximum 20% system wide reduction in water service during extended droughts. However,
7 In 1957 the voters in Palo Alto adopted a measure that requires fluoride be added to the City’s water supply (Palo
Alto Municipal Code Section 12.24.010).
Page 14
recent events have called into question the SFPUC’s ability to maintain a level of service of no
greater than 20% reduction8.
BAWSCA and its member agencies are developing the Long Term Reliable Water Supply
Strategy to quantify when, where, and how much additional supply reliability and new water
supplies are needed throughout the BAWSCA agencies’ service area through 2035. The report
revealed that several agencies have normal year needs in excess of their ISG and all agencies
have varying dry year deficiencies. The report also identified several potential resource
alternatives to address these shortfalls, including desalinization, recycled water, and water
transfers.
The BAWSCA report (Section 3.2 of the Phase IIA report) includes a representation of potential
dry year cutbacks based on historic hydrologic conditions for the period from 1920 through
2002. The analysis used the SFPUC hydrologic system’s operational model to evaluate the
frequency and magnitude of droughts on the system over the 83 years with all WSIP related
projects complete. The results, as shown in Table 2, indicate there is little supply cutback risk
under low demand scenarios, but the risk rises as demands increase.
Table 2: Dry Year Shortfall under different demand scenarios
Demand Scenario
Number of Years of Projected Supply Cutbacks to the Wholesale
Customers Over 83‐year history
18% Average Wholesale
Customer Supply Cutback
(10% System‐wide shortfall)
29% Wholesale Customer
Supply Cutback
(20% System‐wide Shortfall)
Minimum Demand
Scenario (224 MGD) 0 0
Intermediate Demand
Scenario (252 MGD) 7 1
Maximum Demand
Scenario (265 MGD) 6 2
8 Environmental flow requirements at Crystal Springs and Calaveras Dam were greater than anticipated. A 2 MGD
water transfer between the Modesto Irrigation District and SFPUC was also rejected recently by the MID Board.
Page 15
Figure 6 provides a representation of the supply cutbacks that would have been experienced
under the maximum demand scenario using historic hydrologic data with all WSIP projects
complete. The results provide an illustration of the frequency and magnitude of droughts in
the past under the high demand scenario, and are helpful in framing future dry year risks. As
shown, over the 83 year hydrologic period, there would have been 8 years with water
shortages – 6 years with a 10% system‐wide reduction and 2 years with a 20% system‐wide
reduction.
Figure 6: Historic Water Shortages at Maximum Demand Level (265 MGD)
Clearly there is a potential deficiency in SFPUC supplies during dry years, though the overall
impact and frequency will depend on decisions related to dry year contingency plans and future
portfolio adjustments that could be made to remedy the supply deficiency. As identified in the
2010 UWMP, the City has developed a Water Shortage Contingency Plan for implementation
during a drought. The Water Shortage Contingency Plan identifies several stages of drought
response, depending on the degree of supply reduction required. Responses range from
informational outreach to severe water use restrictions and modified rate structures. The City
also has the option of pumping groundwater as supplemental supply in water shortage
situations. This option is discussed in more detail in the section on groundwater.
Emergency Robustness
Since the SFPUC is the City’s only potable supply source, the City is vulnerable to service
interruptions on the SFPUC system. One of the major drivers behind the WSIP was to address
reliability deficiencies, which under some circumstances could have resulted in an interruption
of SFPUC service for up to 60 days following a catastrophic event such as an earthquake. The
Page 16
WSIP level of service objective for seismic reliability is to deliver basic service9 within 24 hours
after a major earthquake. The performance objective is to provide delivery to at least 70 per
cent of the turnouts in each region, and full restoration to meet average day demand within 30
days after a major earthquake. Palo Alto may be better situated than other agencies in having
two distinct connection points to the SFPUC system: three SFPUC connections are served by the
Palo Alto Pipeline connection to Bay Division Pipelines 1 and 2, and two SFPUC connections are
served by Bay Division Pipelines 3 and 4. Figure 7 below is a map of the SFPUC regional water
system.
Figure 7: Map of SFPUC Regional Water System
The City is currently completing the Emergency Water Supply and Storage project. The primary
goal of the project is to maintain basic water service and fire‐flows in all pressure zones in the
City following a catastrophic interruption of SFPUC service. The project allows the City to
maintain water supply in the event that the SFPUC supplies are disrupted.
Environmental impacts
The SFPUC supply is the current baseline supply source for the City of Palo Alto. Subsequent
sections analyze several alternatives to the current and projected supply mix, and the resulting
potential environmental impacts. Increased water use within an agency’s ISG does not require
any action by an agency’s governing body, and therefore does not trigger any California
Environmental Quality Act (CEQA) review obligation.
Sensitivity to Regulations
For many water systems in California, the availability of water supplies depends on many
factors, including legislative and regulatory changes that may impact future supply conditions.
9 Basic service is defined as average winter month usage.
Page 17
The SFPUC system is no different, and has several future regulatory risks that could impact
water supply reliability and/or cost10:
1. Federal Energy Regulatory Commission (FERC) relicensing of the Don Pedro Project
a. State Water Resources Control Board (SWRCB) 401 Certification of FERC
relicense
b. Endangered Species Act (ESA) Section 7 consultation for FERC relicense
2. Central Valley Total Maximum Daily Load regulations
3. Bay‐ Delta proceedings (SWRCB, Legislative actions)
4. ESA Habitat Conservation Plans for SFPUC local watersheds
The SFPUC manages these risks, with support from BAWSCA and the wholesale customers.
VII. Groundwater
The Santa Clara Valley Water District (SCVWD) manages an integrated water resources system
that includes the management of groundwater, supply of potable water, flood protection and
stewardship of streams on behalf of Santa Clara County's 1.8 million residents. The SCVWD
manages ten (10) dams and surface water reservoirs, three (3) water treatment plants, nearly
400 acres of groundwater recharge ponds and more than 275 miles of streams. The SCVWD
provides wholesale water and groundwater management services to municipalities, private
water retailers, and individual property owners operating groundwater wells in Santa Clara
County.
Although the City currently purchases all of its potable water from the SFPUC system, the City
maintains close involvement with the SCVWD as it is an important water wholesaler and the
steward of groundwater resources in Santa Clara County. The city also partners with the
SCVWD on conservation activities. The community is represented on the SCVWD Board of
Directors by the District 7 Director. The City’s mayor also appoints a representative to
represent the City on the SCVWD Commission, an advisory body to the SCVWD Board of
Directors.
The SCVWD’s 2012 Water Supply and Infrastructure Master Plan describes how the SCVWD will
support future water supply needs and reliability. The adopted strategy identifies conservation,
increased recycled water use, indirect potable reuse, additional groundwater recharge ponds,
grey water, imported water reoperations, and dry year options as important components of the
plan.
The City of Palo Alto has several policies embodied in the Comprehensive Plan that relate to
groundwater and water supplies. The policies don’t provide a preference for the use of
10 Source: SFPUC’s 2010 UWMP
Page 18
groundwater, but indicate preservation of groundwater conditions is of critical importance to
the City. The relevant policies are listed below, with program elements, if applicable:
1. POLICY N‐51: Minimize exposure to geologic hazards, including slope stability,
subsidence, and expansive soils, and to seismic hazards including ground shaking, fault
rupture, liquefaction, and land sliding.
2. POLICY N‐18: Protect Palo Alto’s groundwater from the adverse impacts of urban uses.
a. PROGRAM N‐22: Work with the SCVWD to identify and map key Groundwater
recharge areas for use in land use planning and permitting and the protection of
groundwater resources.
3. POLICY N‐19: Secure a reliable, long‐term supply of water for Palo Alto.
Availability
As a city in Santa Clara County, Palo Alto has the ability to pump groundwater with the
understanding that SCVWD will appropriately manage the groundwater resources in the
county. Groundwater conditions throughout the county are generally very good11.
Groundwater elevations have generally recovered from overdraft conditions throughout the
basin since the 1987‐1992 drought, inelastic land subsidence has been curtailed, and
groundwater quality supports beneficial uses.
Background
The SCVWD last published a Groundwater Management Plan (GWMP) in 2001. Since that time,
SB 1938 and other legislation have amended the requirements for groundwater management
plans. The 2012 GWMP was prepared under existing groundwater management authority
granted by the District Act. The purpose of the 2012 GWMP is to characterize the SCVWD
groundwater activities in terms of basin management objectives, strategies, and outcome
measures.
General groundwater conditions in the area are detailed in the SCVWD 2012 GWMP. The City
of Palo Alto overlies the Santa Clara sub basin. The Santa Clara sub basin is divided into upper
and lower aquifers, which are separated by low permeability clays and silts. The SCVWD refers
to these as the shallow and principal aquifer, with the latter generally defined as 150 feet below
ground surface. The principal aquifer is the primary drinking water aquifer, and is the source
for the any increased reliance on groundwater to meet current or future demands. The upper,
or shallow, aquifer is of poorer quality and has limited uses beyond small to medium size
distributed irrigation systems. The SCVWD is responsible for managing the groundwater basin
to ensure there is adequate supply and overdraft conditions are minimized.
The SCVWD accomplishes this goal by maximizing conjunctive use, the coordinated
management of surface and groundwater supplies, to enhance supply reliability. Programs to
accomplish this goal include the managed recharge of imported and local supplies, in‐lieu
11 SCVWD 2012 Groundwater Management Plan
Page 19
groundwater recharge through the delivery of treated surface water12 and acquisition of
supplemental water supplies, and programs to protect, manage and sustain water resources.
Managed and in lieu recharge programs are in balance with withdrawals and the basin is not
currently in overdraft conditions. The groundwater conditions in the Santa Clara sub‐basin
vary, and groundwater pumping from different locations will have different effects depending
on location, elevation, recharge conditions, and pumping activity.
Emergency Water Supply and Storage Project
As part of the Emergency Water Supply and Storage project, the City has refurbished five older
wells, constructed two new wells, and is constructing another new well and a new 2.5 million
gallon storage reservoir and pump station. The primary goal of the project is to improve the
City’s emergency water supply capability. Together with the City’s existing water storage
system, the project will support a minimum of eight hours of normal water use at the maximum
day demand level and four hours of fire suppression at the design fire duration level and will be
capable of providing normal wintertime supply needs during extended shutdowns of the SFPUC
system. The proposed project would provide up to 11,000 gallons per minute (gpm) of reliable
well capacity and an additional 2.5 million gallons of water storage for emergency use. The
groundwater system may also be used to a limited extent during drought emergencies, but is
subject to the following mitigation measures, as stated in the Environmental Impact report (EIR)
completed for the project13:
1. An aquifer test shall be conducted following the City’s well construction and
rehabilitation efforts to verify the basin’s response to pumping; and
2. Emergency demand pumpage shall be limited to 1,500 acre‐feet (AF)14 in one year.
Following this level of pumpage, groundwater production shall be restricted until
groundwater levels recover to pre‐pumping levels.
All wells are currently permitted and designated by the California Department of Public Health
as “Standby” and, as such, can only be used for 5 consecutive days up to 15 days in a year15.
Once the project is complete, the wells may collectively supply up to 1,500 AF per year during a
drought, with restrictions on when the wells can resume pumping following that level of
groundwater extraction. It is important to note that the pumping restriction only applies to the
project as defined in the CEQA documents. This includes the 5 existing wells and 3 new wells.
Individual property owners can install their own wells and pump groundwater.
12 The SCVWD and the Santa Clara County SFPUC customers are partners in conjunctively managing the water
resources in the county. The SFPUC customers in the county have contracts with the SFPUC. The SCVWD has no
contractual relationship with the SFPUC. 13 Environmental Impact Report, Emergency Water Supply and Storage project, Mitigation Measure 3.5‐4(a) & 4(b) 14 1500 AF/Year is equal to 1.34 MGD, or approximately 12% of FY 2012 water consumption 15 California Code of Regulations, Title 22, Section 64414(c).
Page 20
The pumping restrictions for the well system are mitigation measures in the EIR prepared for
the Emergency Water Supply and Storage project. Any increase in the current restriction could
require new or supplemental environmental review. The SCVWD has indicated that the process
to increase the current limitation will require supporting information on the sustainable yield of
the groundwater basin in order to demonstrate increased pumping by the City will not have
significant impacts16.
The capacities of the City’s wells are listed in Table 3. As shown in the table, if all 8 wells were
used full time, they could produce 13.3 MGD, which is equivalent to almost 15,000 AF per year.
Table 3: Projected Well Capacities
Name Capacity (MGD)Status
Fernando 0.5544 Refurbished Well/Fully Operational
Hale 1.8432 Refurbished Well/Fully Operational
Matadero 0.864 Refurbished Well/Fully Operational
Peers 1.872 Refurbished Well/Fully Operational
Rinconada 4.464 Refurbished Well/Fully Operational
Eleanor Pardee 1.296 New Well/Fully Operational
Library 1.008 New Well/Fully Operational
El Camino Park 1.44 New Well/Under Construction
Total 13.3
During the drought in the late 1980’s, substantial pumping by pumpers in the county and
neighboring jurisdictions resulted in a dramatic drop in the groundwater levels in the area. It is
possible that this scenario could happen again during a drought of similar magnitude if
imported water supplies were reduced. The SCVWD adopted level of service goals as part of its
2012 Water Supply and Infrastructure Master Plan effort, including the development of water
supplies designed to meet at least 100% of average annual water demand identified in the
SCVWD 2010 UWMP during non‐drought years and at least 90 percent of average annual water
demand in drought years17. This goal is a countywide goal and includes Palo Alto demands.
Cost
The SCVWD levies a groundwater extraction fee, or “pump tax”, on each acre‐foot of water that
is pumped from the groundwater basin. The charge varies depending on a variety of factors,
including pumpage type (agriculture vs. municipal) and geographic location in the County.
Historically, the cost of groundwater (including the pump tax and the O&M cost of operating a
well) has been comparable to the cost of SFPUC supplies. However, due to the increasing cost
of SFPUC water due to the WSIP, the cost to pump groundwater is projected to be less than the
cost of SFPUC supplies (Figure 8). While the costs of SCVWD groundwater and treated water
16 In summer 2012, staff met with SCVWD representatives to discuss the current limitation and the process to
increase/remove the limitation. 17 SCVWD Board Agenda Item 4.2, June 12, 2012
Page 21
are also projected to rise over the next decade due to capital investment requirements, the
cost of SCVWD water is likely to be less than SFPUC supplies. The vertical lines above the
groundwater and treated water bars in Figure 8 represent the SCVWD high cost scenario, and
reveal that the cost differential between SFFPUC and SCVWD water remains significant even
under a SCVWD high cost scenario.
Figure 8: Projected SFPUC and SCVWD18 Water Rates
0
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$/
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SFPUC vs. SCVWD
SCVWD ‐ Groundwater Rate
SCVWD Treated Water rate
SFPUC Treated Water Rate
ForecastActual
Water Quality
The water quality of the groundwater is considered good, though historically the groundwater
in the area has had iron (Fe), manganese (Mn) and Total Dissolved Solids (TDS) levels that
exceed secondary19 drinking water quality standards.
All potable water scenarios must comply with water quality requirements. Staff currently
samples the wells based on the conditions outlined in the California Department of Public
Health (CDPH) permit(s). The City may be out of compliance with secondary standards on a
18 The SCVWD sets groundwater and treated water rates according to water pricing policies and SCVWD Board
direction. In general, treated water charges are slightly higher than groundwater charges to account for O&M
costs to pump groundwater. However, at times, the SCVWD may adjust rates to encourage use of groundwater
instead of treated water, or vice versa depending on the health of the underground water supplies. 19 Primary drinking water quality standards apply to contaminants that affect health while secondary standards
apply to those constituents that affect aesthetics, taste and odor.
Page 22
short term basis during emergencies, but for full‐time operation the City must be in compliance
with secondary standards or apply for a waiver20. The waiver requires justification and includes
a community survey to establish support for the provision of water that exceeds secondary
standards. The community survey must demonstrate a high degree of acceptance to justify the
waiver.
Key water quality parameters for groundwater, water from the SFPUC and treated water from
the SCVWD are compared in Table 4. All of these sources meet primary drinking water
standards. The table lists several secondary standards and a sampling of other parameters.
Table 4: Water Quality Parameters for Various Water Sources
Water Source Fe
(ppm)
Mn
(ppm)
TDS
(ppm)
Sodium
(ppm)
Hardness
(as CaCo3)
(ppm)
Turbidity
(NTU)
Drinking Water Quality Standard .300 .050 500 N/A N/A 5
SFPUC Water (1) ND ND 132 13.5 57 0.16
SCVWD Treated Water (2) ND ND 209 37 90 0.07
Groundwater (3) 0.25‐1.3 0.13‐0.31 440‐710 75‐170 ‐ 0.33‐7.7
(1) SFPUC values are average water quality values reported by the SFPUC in its 2011 Water Quality Report
(2) Average values from 2011 SCVWD Rinconada Water Treatment Plant Water Quality Data Summary
(3) Based on the City’s well water testing records
ND = non detect
Normal Year Groundwater Supplies
Several treatment and blending options for the wells were evaluated in 2000 in the “Long Term
Water Supply Study”:
1. Blend water with SFPUC water to meet water quality limits for manganese and iron. The
blended water will meet regulatory limits, but will have TDS levels 2‐3 times the current
level in the distribution system21.
2. Provide iron and manganese treatment at each well site. The water will likely not
exceed TDS limits, but it will be 5‐7 times the current levels in the distribution system.
3. Provide iron and manganese treatment at each well site and blend with SFPUC supplies
to reduce the well water TDS levels.
4. Provide iron, manganese and TDS treatment at each well site. The treated water at the
injection point will be comparable to SFPUC supplies.
The estimated present dollar cost of each option is provided in Table 5 for information
purposes. The treatment options focus on the costs to address the elevated iron, manganese
and TDS levels under several water quality scenarios.
20 Title 17 Code of Regulations, Chapter 64449.2 21 Upon completion of the Emergency Water Supply and Storage project, the El Camino Well water can be blended
with SFPUC water in the new 2.5 million gallon storage tank in El Camino Park in a similar manner to Option 1.
Page 23
Table 5: Well Treatment Alternative Preliminary Cost Analysis
Treatment Options22
1 (blend) 2 (treat for
Fe, Mn)
3 (treat for Fe,
Mn and blend)
4 (treat for Fe,
Mn and TDS)
Capital Cost23 (Total for 5 wells) $8.5‐10.8 M $8.5‐10.8 M $9.4 ‐ 11.8 M $37.4 ‐ 46.7 M
Well production
Acre feet per year 6300 12800 2500 12800
% of total Potable Demands 50% 100% 25% 100%
Water Quality24
TDS (500 ppm) 130‐300 440‐700 120 120
Manganese (<0.05 ppm) 0.04‐0.05 <0.05 <0.01 <0.05
Iron (<0.3 ppm) 0.08‐0.3 <0.3 0.05‐0.06 <0.3
The new and refurbished wells are being constructed with chlorine disinfection injection points
and the capability to accommodate fluoride and other needed chemical injection points. The
use of the wells on a regular basis will require a detailed operational plan and some or all of the
sites will need modifications to accommodate backup power, chemical storage, and any
equipment associated with the selected treatment option. Not all sites will have the space to
accommodate these additional requirements. These and other additional operating and capital
costs will need to be incorporated as part of a future detailed cost‐benefit analysis.
The various treatment options will generate waste streams with elevated levels of iron,
manganese, TDS, and chemical residuals used in the treatment process. It is unknown if this
can be discharged to the storm drain system. Options to address this issue include onsite
treatment facilities at each site or discharging the raw waste stream to the wastewater
collection system for delivery to the Palo Alto RWQCP25. In addition to these unknown costs,
there may be several challenges that may need to be addressed related to wastewater
constituent changes from the RWQCP.
Dry Year Groundwater Supplies
The City’s new well and reservoir at El Camino Park is currently being configured to blend with
SFPUC supplies so the El Camino Well can be relied upon to provide groundwater during a
drought up to the 1500 AFY limitation. As a result of blending, the water will meet all
secondary water quality standards, but will be of lesser quality when compared to SFPUC
supplies. To bring the water quality to a level comparable to SFPUC supplies, the City will need
to install Iron, Manganese and TDS filtration at the new El Camino well site.
22 Costs are only those costs incurred by Water Utility. Customer costs, including water softening or filtration
devices will be additional costs borne by individual customers 23 All costs were adjusted from the estimates in the 2000 study to provide a likely cost range in 2012 dollars. 24 Manganese and Iron have single consumer acceptance contaminant levels, while TDS is a consumer acceptance
contaminant level range (recommended = 500; short term= 1000 and upper limit = 1500) 25 Discharges to the wastewater collection system for treatment at the RWQCP have associated costs that are not
included in the preliminary cost estimates.
Page 24
Long Term Reliability
The wells are an important resource during a drought and could be an important resource to
serve a portion of the normal year potable needs in the City. With the current 1500 AFY dry
year groundwater extraction limitation, there is little risk any dry year pumping program could
result in significant impacts to the groundwater basin26.
Since SCVWD manages the groundwater in Santa Clara County, any plans to increase Palo Alto’s
groundwater pumping would need to be discussed with the SCVWD.
Emergency Robustness
The City’s wells are being maintained to provide emergency service during a catastrophic
interruption of SFPUC supplies. If the portfolio changes in the future such that groundwater
becomes part of the normal year supply, emergency preparedness will need to be evaluated
further to ensure the resource can perform under various scenarios. Such an increase could
result in the need for the SCVWD to construct recharge facilities to ensure that the county’s
groundwater supplies are properly maintained. If imported water supplies are required to be
delivered to the recharge facilities, those supplies need to be identified.
Environmental impacts
The use of the wells to meet dry year needs is currently permitted subject to a pumping
limitation of 1500 AF per year. A significant increase to this limitation could require
supplemental environmental review. Staff anticipates issues such as sustainable yield, dry year
availability, subsidence risk, saltwater intrusion, dewatering of local creeks and contaminated
plume migration, would be considered in such an environmental analysis.
Sensitivity to Regulations
An area of concern is future State and Federal water quality regulations for potable water.
Changes in regulations could make the groundwater supply less attractive and more expensive
due to additional treatment. This becomes less of an issue depending on the level of treatment
that is chosen.
26 The 1500 AFY limitation is a CEQA derived mitigation measure that has undergone the public review process.
Page 25
VIII. SCVWD Treated Water
Besides being the manager of groundwater in Santa Clara County, the SCVWD also produces
and delivers treated drinking water to water retail agencies in the county. Long‐term plans of
the SCVWD include extending the treated water pipeline from its current terminus at Foothill
Expressway and Miramonte Road to a Palo Alto connection point at Foothills Expressway and
Arastradero Road (a distance of about 4.5 miles). The SCVWD calls this extension the “West
Pipeline Extension”. However, the project would only be constructed if the City requested
water supply from the SCVWD and signed a treated water contract.
Background
In 1999, the City sent a letter to the SCVWD advising it that information was needed to analyze
the City’s option to connect to the SCVWD treated water West Pipeline. The SCVWD responded
with an estimated cost for the extension of the West Pipeline that would have to be fully borne
by Palo Alto. In February 2002, Palo Alto and four other county retailers requested that the
SCVWD conduct a feasibility study of a West Pipeline extension from both a supply perspective
and the additional reliability of having an additional interconnection with the SFPUC system.
The SCVWD prepared a report on extending the West Pipeline, entitled: “Santa Clara Valley
Water District’s West Pipeline Extension Conceptual Evaluation Final Report”27. The report
evaluated an extension of the existing SCVWD West Pipeline to enable an interconnection of
the Palo Alto and SCVWD systems at Page Mill turnout28. A map of the potential project is
provided in Figure 9.
27 The City of Palo Alto participated in the preparation of the 2012 Water Supply and Infrastructure Master Plan
(WSIMP). As part of that process, staff requested the SCVWD include the West Pipeline extension for project
consideration. The SCVWD noted in the Final 2012 WSIMP that the project is not recommended in the WSIMP
because it does not contribute to long‐term supply reliability. However, the SCVWD stated that it would be
considered during a planned Infrastructure Reliability Master Plan. 28 The SFPUC and the SCVWD have an emergency interconnection near Milpitas that could theoretically be used to
wheel water to Palo Alto. Staff does not anticipate it will be feasible to wheel normal year supplies via the intertie,
but the use of the intertie during dry years may be possible. However, in general the SCVWD system is more dry
year sensitive than the SFPUC system, so it is unclear whether supplies would be available to be wheeled to Palo
Alto via this mechanism.
Page 26
Figure 9: West Pipeline Extension Map
Availability
If the City requested that the SCVWD extend the West Pipeline to serve the City, the terms of
the treated water contract would determine the availability and amount of water that would be
delivered during normal years. The SCVWD has a diverse water supply portfolio, including State
Water Project, Central Valley Project, and local reservoirs. SCVWD’s 2010 UWMP and its 2012
WSIMP indicated the SCVWD anticipates having adequate supplies to meet future needs until
2030 when minor deficits begin to materialize. However, those projections do not assume any
treated water deliveries to Palo Alto. In addition, there is no guarantee that the water will be
available during dry years.
Cost
SCVWD’s West Pipeline Extension Report provided detailed cost estimates for several pipeline
configurations, which are summarized in Table 6. Both scenarios require a new parallel pipeline
from Rinconada Water Treatment plant to the current terminus of the West Pipeline at
Miramonte Road. From there, a new pipeline would be constructed to Page Mill Road. The
cost differential between the two scenarios is largely attributed to different pipe sizing
requirements and an intertie pump station.
Page 27
Table 6: SCVWD Treated Water Connection Summary Costs29
Alternative Assumptions Total Cost
of
Alternative
($million)
Cost to
SFPUC
($million)
Cost to
New
Retailers
($million)
Rate
Increase
to SCVWD
Retailers
($/AF)
Parallel
and
Extension
Existing treated water
contractors and new retailers
share cost of parallel pipe
New retailers pay for extension
94‐114 N/A Palo Alto:
44‐67
Purissima
Hills: 5‐9
$5‐8
Parallel,
Extension
and
Intertie
Existing treated water
contractors and new retailers
share cost of parallel pipe
SFPUC pays for half of
incremental cost of intertie
Existing and new retailers share
cost of extension and half of
incremental cost of intertie
127‐154 18‐22 Palo Alto:
23‐41
Purissima
Hills: 4‐10
Stanford
University:
4‐8
Pump Tax:
11‐14
Treated
Water: 15‐
22
The report concluded that the City and neighboring jurisdictions must pay for the costs of
constructing the extension via a “take or pay” contract, which is a common payment
mechanism for all agencies in the county that purchase SCVWD treated water. The amount of
the take or pay contract is determined by the amortized construction costs divided by the
annual treated water rate. For example, if Palo Alto’s obligation for a West Pipeline extension
was $30 million with an annual cost of $2 million (using an interest rate of 3%/year for a 20‐
year financing period), and the treated water rate was $634.60 per AF30, then Palo Alto would
be required to purchase about 3,150 AF/year, or about 25% of the City’s water usage in FY
2012.
During the term of the contract, the City would have limited ability to adjust its annual water
purchase from the SCVWD. There are several agencies in Santa Clara County that purchase
both SCVWD and SFPUC treated water, and they are subject to minimum “take or pay” contract
provisions by both providers. The City would receive similar treatment. The cost estimates in
Table 6 do not account for any distribution system improvements that may be required to
configure Palo Alto’s distribution system to receive SCVWD treated water.
Recently, the City conducted an evaluation of property tax collected by SCVWD from Palo Alto
property owners. It is not uncommon for water districts to rely wholly, or in part, on property
related taxes to build water systems or for surplus capacity for future users. The SCVWD has
historically relied on taxes to some degree to purchase imported water and fund local
29 Cost of additional supply is not included in project cost. Costs have been escalated 3‐5% from 2003 dollars to
provide a representation of potential costs ranges. 30 This is SCVWD’s treated water rate for FY 2013
Page 28
groundwater and treated water programs, and continues to do so. The results of the property
tax evaluation revealed Palo Alto taxpayers have contributed to the development of the SCVWD
water supply, distribution and treatment system, and will likely continue to do so in the future.
This information could be helpful in determining an equitable sharing of the capital costs of an
extension to serve areas of the county that have historically supported the SCVWD system.
Water Quality
See Table 4 in the groundwater section for a comparison of certain water quality parameters of
SCVWD’s treated water, SFPUC water, and groundwater.
Carollo Engineers evaluated the SCVWD treated water line in the Long Term Supply Study and
provided information on the issues of blending SCVWD supplies with SFPUC supplies. In
general, SFPUC supplies are of superior quality to SCVWD supplies, but there were several
specific issues that were identified in the previous study. If there is interest in moving forward
with an interconnection with the SCVWD system, additional analysis will need to be performed
to determine if the previous issues still remain, and what additional issues have arisen. On the
positive side, the SCVWD’s recent decision to include fluoridation at their treatment plants
removes the need to provide fluoridation at the interconnection points to ensure the water
supply complies with the municipal code. In a similar manner, the SFPUC has completed the
transition to chloramine from chlorine for residual disinfection. This removes some water
quality related issues associated with blending treated water from different sources that use
different disinfectants. However, there may be other issues related to water quality that could
require the two water supplies to be isolated in the distribution system. This would result in
water from difference sources being provided to customers depending on their location in the
distribution system.
Long Term Reliability
It is likely the SCVWD has little surplus imported water to allocate to Palo Alto, so the details of
a potential supply arrangement will need to be evaluated further. During the drought in the
late 1980’s, SCVWD supplies from both the state and federal sources were significantly
reduced. It is not clear what level of drought protection would be provided, though the recent
level of service commitment by the SCVWD indicates that there would be no greater than 10%
reduction in supplies during dry years.
Emergency Robustness
In 2003, the SCVWD initiated the Water Utility Infrastructure Reliability Project to determine
the current reliability of its water supply infrastructure (pipes, pump stations, treatment plants)
and to appropriately balance level of service with cost. The project measured the baseline
performance of critical SCVWD facilities in emergency events and identified system
vulnerabilities. The study concluded that the SCVWD water supply system could suffer up to a
60‐day outage if a major event, such as a 7.9 magnitude earthquake on the San Andreas Fault,
Page 29
were to occur. Less severe hazards, such as other earthquakes, flooding and regional power
outages had less of an impact on the SCVWD, with outage times ranging from one to 45 days.
The level of service goal identified for the Infrastructure Reliability Project was “Potable water
service at average winter flow rates available to a minimum of one turnout per retailer within
seven days, with periodic one day interruptions for repairs.” In order to meet this level of
service goal, the project identified a recommended portfolio to mitigate the risks. The SCVWD
has been implementing the recommended portfolio. The project is expected to reduce the
post‐earthquake outage period from 45‐60 days to 7‐14 days.
In 2007, the SCVWD created a stockpile of emergency pipeline repair materials including large
diameter spare pipe, internal pipeline joint seals, valves, and appurtenances. The stockpile
marks a significant increase in reliability of the SCVWD water supply system, as it helps to
reduce outage time following a large earthquake from approximately 60 to 30 days. The
SCVWD still needs to complete several other emergency planning projects to meet the goal of
reducing outage time to 30 days. These include developing a post‐disaster recovery plan,
developing mutual aid agreements or expanding participation in the California Water/
Wastewater Agency Response Network , setting up contractor, welder, and equipment rental
company retainer agreements, and setting up post‐earthquake pipeline inspection teams. The
addition of groundwater wells and line valves to the SCVWD system will further reduce outage
time following a large earthquake from 30 days to 14 days. The wells will allow the SCVWD to
convey supplies from the groundwater basin to the treated water pipelines following a hazard
event to meet the project’s level of service goal. The line valves will allow the SCVWD to isolate
damaged portions of pipelines.
If the West Pipeline was extended to provide potable water service to Palo Alto, the City would
have one connection to the SCVWD system31, compared to 5 connections to the SFPUC system.
It is unclear what level of reliability would be provided in the event of catastrophic event. The
SFPUC level of service goal following an earthquake is to provide for average wintertime
demands with delivery to 70% of the turnouts within 24 hours following a major earthquake.
The SCVWD level of service goal provides for service resumption to one turnout within 7 days of
a similar event, though the location of a Palo Alto interconnection at the end of the treated
water line may be a weak point, so it is unclear if there will be adequate supplies or system
pressures to provide meaningful service. In addition, the SCVWD plans on extracting
groundwater for raw water delivery to the treatment plants and on to the retailers during an
emergency. The Emergency Water Supply and Storage project will serve this purpose for Palo
Alto.
31 There may be additional connection options to a new SCVWD treated water pipeline, such as a new extension to
the existing Arastradero SFPUC turnout. However, the cost of additional connections was not included in the initial
cost estimate and would likely be borne by the City. Additional connections may allow increased use of and more
efficient distribution of SCVWD treated water, though they may not provide any additional reliability assurances.
Page 30
Environmental Impacts
A West Pipeline extension will require CEQA review. The SCVWD would be the lead agency for
the CEQA process.
Sensitivity to Regulations
The SCVWD imports water from both the State and Federal water projects, and is vulnerable to
actions that impact those sources. Since publication of the 2003 WIRP, federal and state water
deliveries have been reduced on several occasions due to Delta related issues. The Bay Delta
Conservation Plan is currently underway to address the co‐equal goals of water supply
reliability and environmental sustainability. The most likely water conveyance solution will be a
tunnel underneath the Delta from an intake on the Sacramento River to the South Delta
Diversion/Pumping facilities. Such a facility will take decades to build and the costs will likely be
borne by State and Federal water contractors, including the SCVWD.
Page 31
IX. Recycled Water
The City of Palo Alto operates the Regional Water Quality Control Plant (RWQCP), a wastewater
treatment plant, for the East Palo Alto Sanitary District, Los Altos, Los Altos Hills, Mountain
View, Palo Alto, and Stanford University. Approximately 220,000 people live in the RWQCP
service area. Of the total plant flow, about 60 per cent is estimated to come from residences,
10 per cent from industries, and 30 per cent from commercial businesses and institutions.
In 1992, the City and the other RWQCP partners completed a Water Reclamation Master Plan
(Master Plan). The Master Plan identified a three stage implementation for recycled water in in
the RWQCP service area.
In 1995, City Council certified the Final Program Environmental Impact Report (PEIR) for the
Master Plan projects. At the same time, Council decided not to pursue any of the
recommended expansion stages of a water recycling system as the cost could not be justified.
Council adopted a water recycling policy, which included continuation of the existing programs
and monitoring of conditions that would trigger an evaluation of the Master Plan. The Water
Recycling Policy described five conditions that would trigger evaluation of the Master Plan
projects:
1) Changes in the RWQCP discharge requirements
2) Increased mass loading to the RWQCP
3) Requests from partner agencies or other local agencies
4) Availability of federal or other funds
5) Water supply issues:
a. Water shortages
b. Legislative or Regulatory Initiatives
c. Advanced treatment for potable reuse.
Since the Master Plan, the City prepared a recycled water survey in 2006 and a Facility Plan in
2009 for a project to deliver recycled water to the Stanford Research Park. The Facility Plan had
four goals:
1) Define recycled water alternatives and identify a recommended project;
2) Develop a realistic funding strategy
3) Develop an implementation strategy ; and
4) Provide a basis for any future state and federal grant requests for the Project.
Since completion of the Facility Plan, the City initiated the environmental review process for the
project and is currently working on an Environmental Impact Report (EIR) for the project. The
City is also focusing on outside funding sources to improve the project economics.
The Facility Plan provided a comprehensive overview of the proposed recycled water project to
serve the Stanford Research Park. The project would connect to the recently completed
Page 32
recycled water transmission line serving the Mountain View area and extend through the City
to serve the target area. A schematic of the proposed project including water demands and
pipe sizes is provided in Figure 10.
Figure 10: Proposed Recycled Water Project
Availability
The average dry weather flow capacity of the RWQCP is 38 MGD. The average treated
wastewater discharge to the San Francisco Bay is approximately 22 MGD. In theory, all of this
could be captured for reuse. Several RWQCP partners, including Palo Alto, have a contractual
entitlement to the treated wastewater in proportion to the amount of wastewater that is sent
to the RWQCP32. Palo Alto’s FY 2011 flow share to the plant was approximately 39.2%, or 8.624
32 Personal communication with James Allen, RWQCP Plant Manager, November 2012
Page 33
MGD. However, operational constraints and plant configuration limit the recycled water
production capability from the RWQCP.
The RWQCP collaborates with the partners to ensure needed capital improvements for future
recycled water expansion goals are incorporated into long range plans. Considering the
RWQCP’s primary role to provide wastewater treatment services for the partners and to ensure
the RWQCP meets all associated regulatory and permit limitations, the necessary
improvements to accommodate a substantial increase in recycled water deliveries are not a
priority for the foreseeable future. In the meantime, the RWQCP can deliver up to 4.5 MGD of
recycled water via coagulation and filtration through a multi‐layered filter and disinfection
process. This additionally treated effluent meets California Department of Health Services Title
22 requirements for “unrestricted reuse”. The new ultraviolet (UV) disinfection banks can add
6 MGD of recycled water production (8 MGD with an extra bank). The RWQCP plans to use UV
as backup to the filtration/chlorination recycled water treatment train. Future plans include
consolidating the systems into a 10.5 MGD recycled water facility, but this would require some
modifications in plant piping and storage tanks to get bottlenecks out of the system.
In constructing the project to extend the recycled water distribution system to serve the City of
Mountain View, the CPAU Water Fund paid $1 million and committed to pay an additional $1
million connection fee in the event the project to serve the Stanford Research Park was built.
By virtue of this arrangement, the CPAU Water Fund has secured capacity on the pipeline for
future use. The RWQCP cannot currently meet projected recycled water demands under peak
conditions, and additional pumping capacity and possibly storage is needed to accommodate all
project users. Palo Alto’s recycled water project capital costs include the cost of retrofitting the
RWQCP pump station to accommodate incremental recycled water deliveries to serve the
Stanford Research Park.
Page 34
The RWQCP has had a robust recycled water program for many years, including a substantial
amount for RWQCP onsite needs and irrigation at Greer Park, the Duck Pond and the Palo Alto
Municipal Golf Course. As shown in Figure 11, the RWWCP uses about 0.5 MGD annually
(about 560 AFY) for irrigation around the plant as well as some cleaning and treatment
processes. Greer Park and the Duck Pond have each used about 0.04 MGD (45 AFY) on average
over the past five years while the Palo Alto Municipal Golf Course has used about 0.2 MGD (230
AFY) on average over the past five years.
The 2009 Facility Plan identified about 0.8 MGD of new recycled water usage for the project to
expand the recycled water distribution system. The project would primarily serve the Stanford
Research Park area and the bulk (90%) of the recycled water would be used for irrigation
purposes.
Figure 11: Palo Alto Existing Recycled Water Uses for FY 2004‐FY 2012
Page 35
Cost
The Facility Plan included a detailed cost plan to build the project (Table 7). The gross project
cost is approximately $33 million, though this does not include potential outside funding
sources that could lower the project cost.
Table 7: Recycled Water Gross Cost Estimate 1,2
The cost estimates in Table 7 were developed for 2009 Facility Plan using March 2008 dollars
and will need to be updated to reflect current capital and O&M costs. Based on the 2008 data,
the recycled water cost is approximately $2,700/AF, compared to an SFPUC cost of $1260/AF
(2013) to $2240/AF (2020). However, these cost estimates do not reflect several grant and low
interest funding programs that the City has been pursuing that will help lower the unit cost of
the recycled water to a more competitive level with SFPUC costs. These funding options are
listed below:
1. Title 16 ‐ The Bureau of Reclamation's water reclamation and reuse program is
authorized by the Reclamation Wastewater and Groundwater Study and Facilities Act of
1992 (Title XVI of Public Law 102‐575). The City of Palo Alto is a member of the Bay Area
Recycled Water Coalition, a group of regional recycled water projects that collaborate to
pursue federal funding for recycled water projects. In order to receive federal funding,
all projects must receive federal authorization. The City is currently seeking
authorization in the House of Representatives for a federal award of $8.25 million (H.R.
3910). Obtaining authorization is a first step and subsequent steps include submittal of
Page 36
appropriation requests until the full authorized amount is received. While authorization
provides a degree of certainty on a grant award, receipt of the full grant amount will
depend on annual appropriations and the federal political process.
2. Proposition 84 through IRWMP – The City is pursuing Proposition 84 grant funds
through the Bay Area Integrated Regional Water Management Plan. The BAIRWMP
project list was recently updated and the City will have the option to submit funding
requests during future funding rounds.
3. State Revolving Fund Low Interest Loan – The City can apply for low interest
construction loans through the State Water Resources Control Board State Revolving
Fund (SRF) program. The program provides 20 year loans with an interest rate equal to
half of the most recent General Obligation bond interest rate. The most recent SRF
interest rate is 1.7%, though the historical rate is typically in the 2‐2.5% range. SRF
loans have several attractive features, including a payment plan that commences 1 year
after construction and the avoidance of bond issuance costs.
The Title 16 and SRF loan programs represent the best State and Federal funding opportunities
for the project at this time. The City’s recycled water project is on the SRF project list, and staff
does not anticipate that obtaining an SRF loan will be problematic. However, obtaining Title 16
authorization for the project will be critical to making the project economically viable. An SRF
loan and an $8.25 million federal grant would improve project economics such that recycled
water would become competitive with SFPUC potable water within 4‐6 years.
The City’s recycled water project was identified in BAWSCA’s Long‐term Regional Water Supply
Strategy as a project with near term development potential to meet future water supply needs.
Inclusion in the BAWSCA report does not change the project, but it does position the project for
innovative funding opportunities with another BAWSCA agency in exchange for some
equivalent benefit. Such a partnership could be combined with State and Federal funding
sources to further improve project economics.
Water Quality
The recycled water from the RWQCP meets Title 22 requirements for unrestricted reuse. The
main purpose of the Palo Alto recycled water project is to offset the use of high quality
imported SFPUC water for irrigation and cooling purposes. A major challenge for the project is
acceptance by the landscape community of using recycled water for irrigation purposes.
Certain landscapes are particularly vulnerable to the higher salinity that is present in recycled
water, especially those areas with poor drainage and clay soils.
The RWQCP and the plant partners are undertaking efforts to address the elevated salinity
levels in the recycled water by establishing the Salinity Reduction Policy and evaluating the
wastewater collection system for areas where elevated salinity levels indicate Inflow and
Infiltration may be an issue. For example, the City of Mountain View is currently spending $3‐4
Page 37
million to line a sewer trunk line that has indications of saline water intrusion. This large
project may yield a significant salinity reduction when complete in February 2013.
Long Term Reliability
Recycled water is one of the most reliable new water supply sources. As previously mentioned,
CPAU has paid for a future connection to the pipeline that extends from the RWQCP to serve
Mountain View, which has a maximum capacity of 21 MGD. With the addition of the UV banks,
the recycled water production train could provide up to 10.5 MGD of recycled water. As it is
local, it is more reliable than imported supplies, which rely on lengthy networks of pipes, pumps
and storage facilities. In droughts or other water shortage situations, landscape water use is
normally targeted for the largest reductions, but recycled water use would not be subject to
such reductions.
Additional recycled water use will increase the City’s allocations of SFPUC water in drought
times. Since the drought allocation formula is based on both a seasonal component and overall
water use, increased use of recycled water would provide a double benefit since it lowers
potable water use and also reduces the City’s potable usage during the peak irrigation season.
While it is difficult to assess future drought allocations since much depends on the actions of
other agencies, staff estimates the Stanford Research Park recycled water project could reduce
the dry year cutback by 10‐20%.
Emergency Robustness
Recycled water will be used for irrigation purposes and, to a lesser extent, cooling. During a
catastrophic emergency, CPAU will focus on operation of the emergency wells and the potable
distribution system to ensure potable requirements and fire flows are maintained. The RWQCP
will also focus its efforts on returning the RWQCP to normal operations. Recycled water does
not provide additional emergency preparedness improvements over the current situation.
Environmental Impacts
The City has been preparing the requisite National Environmental Policy Act (NEPA) and CEQA
documents for the project. The environmental review process has taken longer than
anticipated, largely due to additional study of the use of recycled water on plants in areas of
poor drainage and clay soils.
Sensitivity to Regulations
The recycled water supply is sensitive to regulations, but these can have both positive and
negative impacts due to the unique nature of the recycled water supply. The RWQCP is subject
to numerous regulatory requirements related to treated wastewater discharges to San
Francisco Bay. The use of recycled water is recognized as one method to reduce discharges to
the Bay and assists the RWQCP in complying with these requirements. For example, in March
2012, the Regional Water Board issued a Water Code Section 13267 Technical Report Order to
Page 38
Bay Area wastewater dischargers, including the RWQCP, requiring submittal of information on
nutrients in wastewater discharges (nitrogen and phosphorus). This information will be
compiled over the next few years and will likely result in the development of future water
quality objectives for the San Francisco Bay estuary. An increase in recycled water use would
decrease the total nitrogen and phosphorus discharge to the Bay. As the regulatory
environment for wastewater treatment plants becomes stricter, recycled water will become an
increasingly useful tool to assist wastewater treatment plants in complying with these new
regulations.
In February 2009, the State Water Resources Control Board adopted Resolution No. 2009‐0011,
which established a statewide Recycled Water Policy. This policy encourages increased use of
recycled water and local storm water. It also requires local water and wastewater entities,
together with local salt/nutrient contributing stakeholders to develop a Salt and Nutrient
Management Plan for each groundwater basin in California. The SCVWD is the lead agency for
this effort in Santa Clara County. Together with the benchmarks in the SCVWD 2012 GWMP,
recycled water impacts on the groundwater basin will likely be monitored and subject to
regulation in the event there are observed changes.
X. Demand‐Side Management
Demand‐side management measures and Best Management Practices (BMPs) are measures
that can be implemented to conserve water. The BMPs are included in the California Urban
Water Conservation Council (CUWCC) Memorandum of Understanding (MOU). Water agencies
that became signatories to the MOU pledged to implement the BMPs and to report progress
biannually to CUWCC.
Since becoming a signatory to the MOU in 1991, the City has saved an estimated 4,135 AF of
water through conservation program implementation. The 2010 UWMP contains the City’s
reports to the CUWCC, including compliance reports on the BMPs. The 2010 UWMP included
an increased conservation program commitment, in large part driven by the requirements of SB
X7‐7.
Availability
BAWSCA has assisted its members in assessing the potential for water efficiency measures. In
October 2008, as part of the adoption of the Water System Improvement Program (WSIP)
Program Environmental Impact Report, BAWSCA coordinated the completion of the Water
Conservation Implementation Plan, which provided a comprehensive analysis of cost effective
conservation measures to identify additional programs that could assist the BAWSCA agencies
in meeting future purchase limitations. Results from the Water Conservation Implementation
Plan were also used to prepare the City’s 2010 UWMP. Figure 12 shows the water conservation
goals Council adopted when it approved the 2010 UWMP. Figure 12 also compares the
Page 39
conservation program commitment in the 2005 UWMP to the new commitments in the 2010
UWMP.
Figure 12: Water Conservation Savings Goals
0
500
1000
1500
2000
2500
2005 2010 2015 2020 2025 2030
Cu
m
u
l
a
t
i
v
e
W
a
t
e
r
S
a
v
i
n
g
s
(
A
c
r
e
-
F
e
e
t
)
Fiscal Year
Actual Savings 2005-2010
Projected Savings from 2005 UWMP
Projected Savings from 2010 UWMP
13% of Water
Demand
4% of Water Demand
The annual report to City Council on efficiency goals and achievements includes a summary for
water demand side management goals and achievements as illustrated in Table 8.
Table 8: Water Savings vs. Goals
Note that the savings goal increased threefold starting in FY 2011. The increase is primarily a
result of legislative requirements (SB 7x‐7) that were captured in the 2010 UWMP. This
aggressive goal is consistent with the City’s longstanding policy of providing cost effective
conservation programs to the community. Staff will monitor conservation program
effectiveness and make necessary adjustments if it appears the current program is not meeting
established targets.
Page 40
Cost
It is the goal of the City to look for opportunities, innovative technologies, and cost effective
programs that best utilize the water conservation budget. In FY 2011, the City dramatically
increased conservation program savings goals to meet the requirements of SB7x‐7. The 2010
UWMP contains a detailed analysis of the current suite of conservation measures that are
offered by the City. For each program, the benefit/cost ratio from the Total Resource Cost
(TRC) perspective is shown. The TRC cost‐effectiveness test compares the total cost of
implementing a measure, regardless of who pays. The costs include the cost of the device, any
installation costs, and the implementation costs of the program (advertising, tracking,
performance monitoring, rebate processing, etc.). The benefits include the avoided costs of
water purchases. The Water Utility assesses each measure in terms of financial impact to the
utility, which includes rebate costs as well as any other administrative costs borne by the Water
Utility. The water savings summary through 2030 is provided in Table 9, including cost to the
utility.
Table 9: Conservation Program Costs33
2015 2020 2025 2030
Total Savings (Acre‐feet) 672 560 168 448
Total Wastewater Savings (Acre‐feet) 403 314 67 157
Total Outdoor Savings (Acre‐feet) 269 246 101 291
Utility Implementation Cost ($2010) $754,058 $370,843 $364,762 $387,604
Cost/Acre‐feet $1,122 $662 $2,171 $865
Table 9 illustrates that the aggregate conservation program is cost effective when compared to
SFPUC supply alternatives.
As the cost of SFPUC water increases, many conservation programs become more cost
effective, though the Water Utility adjusts conservation programs depending on several factors,
including program penetration, community preferences and the TRC. Despite the very
aggressive targets in the 2010 UWMP, it may be possible to further increase conservation
program utilization to achieve additional savings.
Water Quality
Demand side measures do not present any water quality issues.
33 The large increase in cost per acre foot in 2025 reflects regular captured savings less a drop off of savings from
those measures initiated in the 2012‐2020 time frame that begin to reach maturity. Water agencies offer rebates
to make it more attractive for customers to install more efficient, and potentially costlier, measures. At some
point in the future the measure reaches the end of its useful life and must be replaced. For some measures, the
models assume the consumer will only have the choice of the more efficient model in the future and therefore no
rebate is needed anymore. Absent a rebate, the Water Utility does not account for the savings anymore.
Page 41
Long Term Reliability
Staff forecasts and tracks DSM program effectiveness, but the ultimate effectiveness for
different programs varies substantially depending on many factors, including individual
behavioral patterns. Much research has gone into evaluating the reliability of DSM, and some
of that research could be useful to the City in future efforts to plan and evaluate program
effectiveness. Due to the large differential between water demand and the City’s Individual
Supply Guarantee, there is no pressing need to strictly monitor DSM program effectiveness like
there may be for an agency that is at risk of exceeding its Individual Supply Guarantee
Water efficiency during a drought is a more complicated issue. One issue is the concept of
“demand hardening”, which is the assumed loss of demand elasticity during a drought that
results from water conservation programs implemented before the drought. In other words,
the community may have little flexibility to reduce demand further if conservation programs
have been truly effective. At the same time, there are certain DSM measures that are not
suitable during normal years that can be implemented during dry years and achieve desired
savings (i.e ‐ steep rate increases, irrigation restrictions).
Emergency Robustness
The 2010 UWMP contains a summary of demand side options that can be implemented under
various scenarios (Section 7 – Water Shortage Contingency Plan). During a catastrophic
interruption of SFPUC supplies, the City will immediately initiate emergency supply options to
meet potable demands and fireflow requirements. At the same time, the City will begin
informational outreach programs to inform the community that emergency conditions are in
effect and water consumption behavioral changes are required (i.e no irrigation).
For dry year scenarios, the City will implement informational outreach programs, incentive
based demand‐side management programs, and water audits. In addition, rate schedules may
be modified, as appropriate, to reflect the water shortage conditions. Due to the
SFPUC/BAWSCA drought allocation formula, conservation programs provide a benefit in
reducing dry year cutback requirements. Conservation programs that specifically target
irrigation demands will provide an additional benefit because of the seasonal component of the
drought allocation formula.
Environmental Impacts
For the most part, demand side measures do not present any environmental issues. Measures
that specifically target landscape conversions or efficiency changes have occasionally been the
subject of concern by tree advocacy groups who are concerned about impacts on trees due to
decreased landscape watering. The City includes information on proper tree maintenance for
those customers converting to drought resistant landscapes.
Page 42
Sensitivity to Regulations
Demand side measures are not limited by any regulations. However, additional requirements
to implement measures may be proposed, or compliance with certain efficiency standards (e.g.
per capita water use) may be required, especially if seeking State or Federal grant or loan
assistance for a project such as the recycled water project.
XI. Individual Supply Guarantee Sale
Availability
The City currently purchases approximately 12 MGD of potable water from the SFPUC and has
an Individual Supply Guarantee (ISG), of 17.07 MGD. A sale of surplus ISG could generate
income for a variety of potential purposes. Over the past several years there has been
increased interest in an ISG transaction, but the mechanism and value of the ISG has been
difficult to establish, and this has hindered movement on this issue.
The City’s current water use is approximately 12 MGD, and the recent 2010 UWMP forecasted
the City’s water use would increase slightly in the next few years, and then remain flat around
13.6 MGD through 2030. In the event the City transferred 1‐2 MGD of its ISG to another party,
recent forecasts do not anticipate this will impact the City’s ability to meet normal year potable
demands.
The SFPUC/BAWSCA (Tier II) drought formula is based on the weighted average of two
components, the smaller of which is the ISG34. This is beneficial to the City since current
consumption is well below the City’s ISG. An ISG transfer would reduce that benefit and result
in an increased dry year reduction requirement by the City. At the same time, this aspect of the
role of the ISG in the drought formula would be viewed favorably by a purchasing entity as it
would be acquiring normal year supply and improving its dry year allocation.
There are several possible uses for the funds from an ISG transaction, including increasing dry
year supply reliability. Examples of potential projects that could reduce the dry year supply
deficiency include retrofitting the City’s wells to provide high quality groundwater, arranging a
dry year water transfer arrangement that could be wheeled via the SFPUC system, or providing
the funds necessary to complete the recycled water project, which is a “drought‐proof” water
supply resource.
Cost
In May 2010, the Purissima Hills Water District indicated an interest in purchasing 0.5 MGD of
the City’s ISG for a one‐time payment of $1 million. The City declined the offer, citing several
34 It is important to emphasize the Tier II formula expires in 2018, unless extended by mutual agreement of the
Wholesale customers. It is possible the successor agreement to the current Tier II formula could be quite
different, including a larger or smaller role for the ISG.
Page 43
policy issues that needed resolution prior to any action to initiate an ISG transaction. With
completion of the Tier II drought allocation process and the Interim Supply Limitation allocation
process, the major policy obstacles have been addressed.
In September 2012, the City of Brisbane executed a term sheet with the Oakdale Irrigation
District to transfer water to Brisbane. The transaction will require additional agreements with
the Modesto Irrigation District and the SFPUC as intermediate parties. As is the case with
PHWD, Brisbane’s water use is close to its ISG and it needs additional supplies to meet
anticipated needs. The term sheet is a preliminary step, but it provides a starting point to
establish a proxy value for an ISG transaction. The term sheet contemplates a sale of up to
2,400 AFY, with a price of $500/AF for any delivered water and a price of $100 for any water
not delivered (i.e, the difference between 2,400 AF and the delivered quantity). After five
years, Brisbane must notify Oakdale Irrigation District how much water will be taken during the
remainder of the agreement. All of that water is paid for at $500/AF, regardless of whether or
not it is actually taken. If the City were to execute an agreement similar to the
Brisbane/Oakdale transaction, a 2 MGD transfer might generate revenues of $224,000 to $1.1
million per year for the first five years, followed by up to $1.1 million per year for the duration
of the transaction. Of course, such a transfer would also reduce the City’s ISG from 17.07 MGD
to 15.07 MGD.
Water Quality
A water transfer does not present any water quality issues.
Long Term Reliability
A 2 MGD water transfer would reduce the City’s ISG from 17.07 MGD to 15.07 MGD. The City’s
current normal year water use is well below 15.07 MGD, and recent forecasts indicate that the
City’s usage will exceed 15.07 MGD for the foreseeable future. For dry years, a reduction in the
City’s ISG will result in an increased water reduction requirement. For dry years, the Tier II
drought allocation formula has an ISG component so a reduction in ISG will negatively impact
the City’s allocation during a drought. Staff estimates a 2 MGD sale would require an additional
5‐7% dry year cutback from the City or could increase reliance on groundwater. A thorough
evaluation of such a sale is necessary to provide a more detailed assessment.
Emergency Robustness
A nominal ISG transfer would not impact the City’s access to SFPUC supplies following a
catastrophic interruption of SFPUC supplies.
Environmental Impacts
Staff anticipates that the receiving party will initiate any required environmental review under
CEQA.
Page 44
Sensitivity to Regulations
An ISG transaction is subject to Section 3.04 of the WSA. The SFPUC review is limited to
determining if the proposed transfer complies with the Raker Act and whether the affected
facilities in the Regional Water System have sufficient capacity to accommodate delivery of the
increased amount of water to the proposed transferee. Section 3.04(a) of the WSA also
specifies the City may “transfer a portion….to one or more other Wholesale Customers...”, thus
indicating an ISG transaction will likely be limited to another Wholesale Customer, or a third
party that plans on receiving the water within the service territory of another Wholesale
Customer.
Attachment B
Draft Requirements for Submittal of a Determination of the effects of groundwater pumping on
nearby buildings, infrastructure, trees, or landscaping.
Required information to be submitted in a report prepared by a qualified professional, to include
following:
Describe alternative construction methods considered by the owner/applicant and explain why
dewatering is proposed for the project.
Submit the following information:
o Depth to groundwater, maximum depth of excavation (including utilities, pits, shafts,
etc.) and proposed maximum depth of dewatering wells/pumping.
o Description of dewatering technique, including: location of dewatering wells, size and
anticipated flow from each pump. Include a schematic diagram showing pipe and pump
sizes and locations and sizes of all tanks, fill station, pipe route to nearest storm drain
inlet (including flexible and rigid pipe locations), and all street and sidewalk impacts
including trenching, sawcuts, and asphalt patching between project site and storm drain
inlet.
o Anticipated dewatering flow rate and total dewatering duration.
o Controls to be utilized (e.g., settling tank, turbidity curtain, etc.)
o Location of anticipated discharge including final receiving water (Creek name or Bay)
o All wells and other dewatering sites within a 400 foot radius (roughly one City block) of
the property that may interact with dewatering activity, using information available
from the City. State or show the exact location of these dewatering sites.
o Determine the radius of influence (i.e. extent of cone of depression) from each
dewatering well as a function of time, based on local soil and groundwater conditions.
Prepare a map and cross sections of the cone(s) of depression. State whether it is
reasonably likely that the proposed dewatering will cause effects (including settlement
or movement) on off-site structures or infrastructure, including the right or way,
easements, and utilities within public utility easements. State whether it is reasonably
likely that the proposed dewatering will reduce the amount of water taken up by any
vegetation or trees to a level that will affect the health or viability of the vegetation or
trees. Utilize an Urban Forestry Sub Consultant (certified arborist) to verify any such
effects on trees.
To the extent that the qualified professional states that off-site effects are reasonably likely to
occur, identify and implement avoidance measures to minimize the type and severity of those
effects. Avoidance measures are also to be employed to the extent practical to minimize the
PUBLIC WORKS
P.O. Box 10250
Palo Alto, CA 94303
650.329.6951 January 2016
Attachment B
flow rate and duration of the pumping, even when off-site effects are not specifically identified.
Avoidance measures may include, for example: reducing well count, well depth, well location,
pumping rate, and/or duration of pumping; supplemental irrigation of trees or vegetation, soil
amendment, or other plant protection methods recommended by a certified arborist;
alternative dewatering or construction methods.
Develop a monitoring plan to assess any actual effects on vegetation, trees, structures and
infrastructure.
The geotechnical study and description and extent of the cone of depression must be stamped
by a California licensed Geotechnical Engineer and submitted to the City. This report will be
made available for public review.
Attachment C: Correspondence
fo ... "T M11~ '5~1\-o
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I would like to clarify that savepaloaltosgroundwater.org is NOT
against building residential basements. Basement construction presents
many potential problems but our focus remains on dewatering and the
treatment of community groundwater as a vital community resource;
not as construction waste.
1/ 4 /1(p
The Policy and Services Committee voted unanimously to send the issue
of dewatering to the full City Council for discussion.
The Department of Public Works will present a 3 tiered approach
including formulation of a site specific plan for any property issued a
dewatering permit.
We ask the City Council to direct Staff to include in their
recommendations the following:
1. All community groundwater removed during construction shall
be redirected and I or reused; the Site Specific Plan shall describe
how the pumped water will be used and/ or the method of replacement
into the aquifer. Directing ground water into the storm drain is no
longer acceptable.
2. All extracted groundwater shall be metered; this will provide, for
the first time, an accurate measurement of the amount of pumped
groundwater. Palo Alto can use this information to establish a
database of extracted groundwater which will be useful for many
purposes.
3. During dewatering, the amount of permitted groundwater
extraction shall not exceed a volume equivalent to water covering
the lot to a depth of 5 (five) feet. Installation of monitoring wells
near and further from the construction site, as well as making this
information easily available for public review should help monitor the
effects on the water table, and should remain in place for a period of
time long enough to estabHsh recovery of the water table following
pumping.
4. The dewatering process shall be limited to 1 month .. Best
construction praCtices, specifically having all contractors and
subcontractors sequentially scheduled, should reduce excessive
,,
dewatering. Significant daily fines, similar to those for sedimentation
discharge, should be assessed when dewatering exceeds allowed time.
This would help put in place incentives for using best construction
practices.
5. A basement design, which does not impede the flow of water
through the surrounding soils especially during normal or
exceptional rainfall, shall be part of all site specific plans. The
basement must not present a flood or subsidence danger to
surrounding homes.
In addition, we request the City Council apply the same Planning and
Review requirements to all basement construction requiring dewatering
as would apply to a 2 story home. Application of the FAR, and limiting
basement depth, as previously discussed, should be considered.
Members of Savepaloaltosgroundwater.org look forward to continuing
our work with the Council and Staff to address the issues we discussed
this evening.
Thank you,
Rita Vrhel
Draft guideline for the maximum permissible quantity of water to be removed by dewatering
(for residential basements)
Save Palo Alto’s Groundwater
Current Practice
For a typical 15 foot deep dewatering for a 2500 square ft. basement on an 8,000 square foot
lot, and assuming that 80% is dirt and the other 20% (0.2) extractable groundwater, the
maximum amount of water attributable to the lot to be pumped would be 8,000 ft2 x 15 ft x 0.2
= 24,000 ft3. The City estimates the typical amount of water pumped per basement to be 1.2
million ft3. Therefore, at most, 24,000 / 1,200,000 x 100% = 2% of the water is from the
property being dewatered. This corresponds to water 150 feet deep over the entire property!
Obviously, the remaining 98% is from surrounding properties. How is this fair to surrounding
homeowners and to the greater community at any time, and especially in a time of drought and
water restrictions?
Proposed Requirement
The guideline for limiting the amount of water removed during dewatering to five (5) feet per square
foot of lot, i.e. a maximum of 40,000 cubic feet (300,000 gallons) from a 8,000 square foot lot was
developed from two considerations:
1) Sustainability. The amount of rainfall on a lot is about 1.25 feet per year times the area of the lot.
Of this, Todd Engineers estimated that 5 – 10% (0.0625 – 0.125 feet times the area) enters the
shallow aquifer, and then potentially the deeper aquifer levels. The remainder either runs off,
evaporates or is taken up by plants. Therefore, 5 feet of water depth corresponds to 4 years of
(normal) rainfall or 40 to 80 years of absorption by the aquifer of rainfall from the specific
property. For 15 dewatering projects, the amount of water pumped would correspond to
groundwater accumulation from 600 – 1200 residences for an entire normal year.
2) Reducing groundwater withdrawn from surrounding properties. As noted above, the amount of
water under a property can be estimated by the product of the area of the property, the
distance that the water table is lowered and the effective porosity of the soils. The effective
soils provide an estimate of the amount of water that will flow out of soils under gravity. The
values range widely but for clays, the effective porosity of clay ranges from 0.01 – 0.18,
(http://web.ead.anl.gov/resrad/datacoll/porosity.htm).
For a basement that lowers the water table from 7 feet to 15 feet under the property, and 0.18
porosity (the high estimate), the amount of water from the property would be (15 – 7) x 0.18 ft
= 1.44 feet of water covering the entire property.
Permitting withdrawl of 5 feet of water per square foot means that at least (5-1.44)/5 = 71% of
the water would come from surrounding properties. . In cases where the water table is lowered
less, or the soils are less porous, a larger fraction of the water would come from surrounding
properties. For example, if the water table was lowered 2 feet, and the same amount of water
was pumped, then >90% of the water could come from surrounding properties.
0
CITY OF
PALO
ALTO
Overview
Guidelines for Dewatering During Basement
Or Below Ground Garage Construction
February 2016
On February 1, 2016, Palo Alto City Council strengthened requirements designed to minimize the pumping
and discharge of groundwater from basement (or below ground garage) dewatering during construction.
Pumping of groundwater after the completion of basement construction has not been permitted for over a
decade. In recent years, concerns that construction dewatering may be wasting water, potentially damaging
structures, trees and vegetation, and depleting or altering the flow of groundwater, have arisen. Therefore
Palo Alto has added new requirements.
Public Works only allows drawdown well dewatering of groundwater. Open pit dewatering of groundwater
is disallowed. Open pit dewatering is allowed for rainwater that may accumulate at the bottom of an
excavation, if water quality limits are met.
Groundwater dewatering is only allowed from April through October due to inadequate capacity in the
City's storm drain system. Open pit dewatering of rainwater is allowed throughout the year, but must meet
water quality requirements.
A geotechnical report must be submitted for the site (separate from the Geotechnical Study described
below), and must list the highest anticipated groundwater level. Public Works recommends a piezometer to
l ··;\
be installed in the soil boring. The contractor must determine the depth to groundwater immediately prior
to excavation by using the piezometer or by drilling an exploratory hole if the deepest excavation will be
within 3 feet of the highest anticipated groundwater level. If groundwater is found to be within 2 feet of the
deepest excavation, a drawdown well dewatering system must be installed, or, alternatively, the contractor
can excavate for the basement without a dewatering system in place and hope not to hit groundwater.
However, if groundwater is hit, the contractor must immediately stop all work and must meet all of the
following requirements prior to resuming work.
Public Works may require water to be tested for contaminants prior to initial discharge and at interval
during dewatering. If testing is required, the contractor must retain an independent testing firm to test the
discharge water for the contaminants Public Works specifies and submit the results to Public Works.
Below is a summary of the pre-existing requirements, with the recently adopted requirements included. The
overall goal is to minimize the discharge of groundwater from basement construction dewatering. The
requirements fall into four categories: 1) Fill stations are required so that others may fill water trucks or
connect garden hoses for irrigation; 2) Use plans are required to demonstrate that the applicant/builder is
arranging for use of as much of the pumped water as possible and minimizing storm drain discharge; 3) A
Geotechnical Study is required (unless the owner/builder received the Planning Conditions of Approval, or
submitted a Building Permit Application before January 14, 2016) to determine any potential effects and
needed avoidance measures; and 4) Street Work/Dewatering permits are required (and are issued after
requirements #1, #2 and #3 are completed).
1. Fill Station Requirements
Fill Station requirements are explained in the attached "Fill Station Requirements" and are summarized
in the check-list shown below:
a) Locate the fill station box outside the fence to allow 24-hour per day access;
I b) Provide 2 Yz" fire hose connection with a 25-foot ( minimum ) fire hose;
c) Provide at least two hose bibs outside the fill station box for standard hose connections;
d) Provide sufficient pressure to deliver 200 gallons per minute (gpm) in the fire hose and 10 gpm in
the garden hose;
e) Provide a "Water Filling Station" sign on the fill station box;
f) Provide a "Non-Potable Discharge" sign on the discharge point;
g) Supply log sheets, and a pen inside the box for truckers to show date and amount of filling;
h) Provide a fill station box combination lock and give City the combination (617-3103);
i) Provide sufficient flow meters and data loggers to determine both the water used through the fill
station and the total water pumped from the ground;
j) Protect against trip hazards with sidewalk bridges and appropriate signage as needed;
k) Once water is in the tank, call Watershed Protection ( 650-329-2430/2122) for water quality testing;
I) When Fill Station is ready, call Public Works Engineering Inspection (650-496-6929) for inspection;
(Note: When the City determines that the site is too close to an area of ground water
contamination, no fill station shall be provided.)
' ·.'
2. Use Plans
A brief groundwater use plan must be prepared to show how the groundwater will be used to the extent
practical. It shall be submitted with the Street Work/Dewatering Permit Application, and shall contain
the following minimum provisions:
a) Applicant distribution of City-provided door-hangers to advertise the availability of water; these are
to be collected if still apparent after 24 hours.
b) Applicant watering of on-site and neighboring vegetation, to the extent desired by owners;
c) Applicant piping water to any nearby parks and schools as requested by City;
d) Applicant trucking water one full-day per week to irrigation sites as directed by the City;
e) Applicant using water on-site for dust suppression and other construction needs.
3. Geotechnical Study I Determination of Effects and Associated Avoidance Measures
Conduct a Geotechnical Study to determine the radius of influence (i.e. extent of cone of depression)
from each dewatering well as a function of time, based on local soil and groundwater conditions. All
wells and other dewatering sites within a 400-foot radius (roughly one City block) of the property that
may interact with dewatering activity, using information available from the City, shall be included in the
City of Palo Alto (ID # 6700)
City Council Staff Report
Report Type: Informational Report Meeting Date: 4/11/2016
City of Palo Alto Page 1
Summary Title: Update on Recycled Water Planning Efforts and Groundwater
Studies
Title: Update on Recycled Water Planning Efforts and Groundwater Studies in
partnership with Santa Clara Valley Water District
From: City Manager
Lead Department: Public Works
Recommendation:
This report is provided for information only and requires no Council action.
Executive Summary
The purpose of this report is to provide Council an overview of the advances being
made to develop alternative water supplies, both regionally and in Palo Alto.
Alternative water supplies include:
Recycled Water from wastewater plants like Palo Alto’s;
Purified Water from reverse osmosis plants like San Jose’s;
Increased groundwater use coupled with groundwater recharge;
Local rainwater/storm drain system harvesting;
Sub-regional wastewater “scalping” plants for small communities/districts;
and
Individual building use of graywater and treated blackwater.
Palo Alto is working through a variety of groups and committees to conduct
planning for alternative water supplies. Key collaborators include Palo Alto’s five
Partners in its Regional Water Quality Control Plant (RWQCP), the other recipients
of San Francisco PUC (Hetch-Hetchy) water, and other agencies in Santa Clara and
San Mateo Counties. An important next step is the execution of several contracts
to explore the potential use of key alternative supplies.
City of Palo Alto Page 2
The first such contract is a feasibility study on the installation of an advanced
water purification system, such as reverse osmosis, at the RWQCP. The second
would update the 1992 Recycled Water Master Plan by studying groundwater
recharge potential for indirect potable reuse, further utilization of recycled water
by more RWQCP Partners, connections with the Sunnyvale distribution system,
and other potential recycled water activities. The Santa Clara Valley Water District
would provide much of the funding for this work and help manage the various
tasks.
Background
The RWQCP produces high quality recycled water which is a drought-proof, locally
controlled, non-potable water supply. Recycled water will help reduce Palo Alto’s
reliance on imported water supplies. The RWQCP currently produces recycled
water in excess of the current demand; therefore staff is working to expand the
recycled water demand and distribution system. As such, the City of Palo Alto
certified an Environmental Impact Report on September 28, 2015, to expand
recycled water through South Palo Alto to Stanford Research Park (CMR# 5962).
This proposed expansion project is phase III of the 1992 Recycled Water Master
Plan. Additionally, the Santa Clara Valley Water District is seeking alternative
water supplies from local wastewater treatment plants. There are three
wastewater treatment plants that discharge into San Francisco Bay within Santa
Clara County: (1) San Jose/Santa Clara Regional Wastewater Facility (San Jose
RWF), (2) City of Sunnyvale and (3) the RWQCP. The Water District already has
partner agreements with San Jose RWF and the City of Sunnyvale. Recently the
Water District approved a partner arrangement with the City of Palo Alto to fund
eighty percent of the Advanced Water Purification System Feasibility Study
Contract. The Feasibility Study will evaluate alternatives including treatment to
reduce improve recycled water quality.
As part of the effort to expand uses of recycled water, the City and Water District
are developing a further understanding of the northwest county groundwater
system to identify opportunities for enhanced groundwater recharge.
Discussion
For the past year staff have been working with the Santa Clara Valley Water
District and the RWQCP partner agencies to research expanding recycled water
use opportunities in Northwest Santa Clara County. The City is working on
City of Palo Alto Page 3
updating the Recycled Water Master Plan to produce a strategic plan that will
include the following information:
Advanced Water Purification System Feasibility Study
White paper on initial description of all water sources
White paper on satellite and onsite treatment and reuse of black water,
grey water, and stormwater
Ongoing Palo Alto Potable Water Supply Resource Planning
Mountain View Recycled Water Distribution Expansion and potential
Sunnyvale Tie-In
Palo Alto Recycled Water Phase III Expansion Project business plan
development, preliminary design, and securing of outside funding
Northwest Santa Clara County Groundwater Study for Indirect Potable
Reuse (IPR) Potential
Palo Alto RWQCP Partner Agencies Recycled Water Expansion
In addition to the upcoming Recycled Water Strategic Plan, staff has been working
on the following Recycled Water planning projects.
Advanced Water Purification System Feasibility Study (contract in process)
To expand the use of recycled water to include cooling towers and the irrigation
of salt-sensitive landscaping, staff is working to reduce the total dissolved solids
(TDS) concentration. Consequently, the City has partnered with the City of
Mountain View and the Santa Clara Valley Water District to jointly fund a
feasibility study for installation of an advanced water purification system (AWPS)
at the RWQCP (CMR #6458). The AWPS would produce virtually TDS-free water
which could be blended with the current recycled water to achieve a TDS
concentration of 450 ± 50 parts per million (ppm).
White Paper on Initial Description of all Water Sources
At the 2015 Council Meeting approving of the Environmental Impact Report (EIR)
for the Phase III Recycled Water Expansion, Council requested further information
on water sources as they pertain to the City of Palo Alto. Attached is an initial
description of all water sources (potable and non-potable) potentially available to
the City of Palo Alto (Attachment A). Potable water refers to water that meets
drinking water standards and is considered safe to drink; while non-potable water
refers to water that does not meet drinking water standards and is considered
City of Palo Alto Page 4
unsafe to drink.
White Paper on Satellite and Onsite Treatment and Reuse
City staff has been tracking satellite and onsite treatment systems and reuse.
Staff will be collecting information on similar efforts regionally and nationally,
including the development of standardized design criteria and regulations.
Currently, in the RWQCP service area, there are a few facilities that have reused
gray water and stormwater for irrigation purposes. Stanford is currently
researching an onsite treatment system.
Ongoing Palo Alto Potable Water Supply Resource Planning
City staff is currently working on the Water Integrated Resources Plan (WIRP) that
will discuss the variety of potable water supply resources and planning. The WIRP
will include an assessment of alternative potable water supplies including the
City’s current water supply source from the San Francisco Public Utilities
Commission’s Region Water Supply System, groundwater, and treated water from
the Santa Clara Valley Water District as well as demand-side management.
Recycled water will be assessed both as a tool to reduce potable water demand
and as a potential potable water supply through IPR and Direct Potable Reuse
(DPR). The results of the groundwater study discussed below will be an important
part of this analysis. All of these resources will be evaluated based on availability,
cost, water quality, environmental impact and robustness in water emergencies
and with respect to potential state regulations.
Mountain View Recycled Water Distribution Expansion and Sunnyvale Tie-in
Mountain View currently receives the majority of the recycled water produced at
the RWQCP. Mountain View has hired a consultant to research expanding the
recycled water distribution system within its city limits and is working with
Sunnyvale for a potential recycled water intertie. The City of Sunnyvale is
rebuilding their wastewater treatment plant and plans on treating the majority of
their flow to purified water for future IPR. Therefore, their existing recycled
water customers will need a new source of recycled water which will potentially
be provided by the RWQCP via the Mountain View—Sunnyvale intertie.
Palo Alto Recycled Water Phase III Expansion (RFP in process)
The City is seeking a consultant to develop a business plan, preliminary design,
and aid in securing funding for the Phase III Expansion project. This evaluation
City of Palo Alto Page 5
will help Council decide on pursuing Phase III Expansion of the recycled water
pipeline. The City has drafted interim Recycled Water Guidelines to help facilitate
new recycled water customers who are on the existing recycled water line near
the RWQCP.
Northwest Santa Clara County Groundwater Study for Potential Indirect Potable
Reuse (RFP in process)
The purpose of the groundwater study is to compile baseline information on the
current condition of aquifers in northwestern Santa Clara County and adjacent
areas, including sources and quantities of recharge, groundwater pumping, and
water quality. This information will be used to evaluate the feasibility of IPR of
advanced treated recycled water and identify opportunities for increased
groundwater utilization of recycled water. This study will also evaluate impacts to
groundwater resources from potential pumping or recharge projects to ensure
continued sustainable groundwater management.
Palo Alto RWQCP Partner Agencies Recycled Water Expansion (RFP in process)
City staff is seeking opportunities to expand recycled water within the RWQCP
service area: East Palo Alto, Los Altos, Los Altos Hills, Mountain View, Stanford,
and Palo Alto. The RWQCP’s NPDES permit requires the treatment plant to have a
recycled water program. Current recycled water demands and distribution
systems were identified in the Recycled Water Master Plan that was completed in
1992. Since 1992, prolonged drought and increased economic activity has
opened up new potential demand for recycled water in partner cities, including
potential groundwater recharge opportunities. Consequently, staff is pursuing a
consultant to re-evaluate the current and projected recycled water demand in the
RWQCP service area.
Timeline
Below is a tentative timeline for the recycled water projects:
Cost sharing agreements with the Santa Clara Valley Water District and City
of Mountain View for the Advanced Water Purification System Feasibility
Study – April 2016
Recycled waterpipeline expansion within East Palo Alto, Palo Alto and
Mountain View – Construction expected to begin in 2016
Advanced Water Purification System Feasibility Study expected to be
City of Palo Alto Page 6
completed by end of 2016
Recycled Water Strategic Planning and Groundwater Assessment contract
expected to be approved in summer 2016; the following deliverables will be
completed by December 2018:
o Phase III Recycled Water Expansion Business Plan, Preliminary Design
& Secured Funding Effort Report
o IPR Feasibility Evaluation
o Conceptual Groundwater Model
o Northwest Santa Clara County Groundwater Study for Potential IPR
Report
o Recycled Water Strategic Plan Report
o Funding Identification & Application(s)
o Public Outreach
Resource Impact
The current recycled water program consists of five hard-piped City facilities and
more than 60 permitted users of the recycled water truck fill station. The RWQCP
is the wholesaler of recycled water within its service area. The City is currently
negotiating private hard-piped recycled water customers along the existing
distribution line,expanding recycled water into East Palo Alto and in South Palo
Alto including Stanford Research Park.. City staff anticipate construction of the
East Palo Alto recycled water expansion to commence in 2016; therefore, staff is
needed to help manage future contractors. As mentioned previously the City is
planning on managing larger recycled water planning contracts to improve the
water quality, update recycled water strategic plan, and investigate the possibilty
of indirect potable reuse to recharge groundwater. The City is currently
negotiating with the Santa Clara Valley Water District that they will fund eighty
percent of the Advanced Water Feasibilty Contract and the City is still negotiating
how much the SCVWD will fund of the second contract that will update the
recycled water strategic plan. The City currently does not have a dedicated staff
person who works on recycled water. In order to expand the City’s Recycled
Water Program, a new Senior Engineer is required for future tasks including:
Initiate and manage recycled water and water re-use consultant contracts
Prepare a new Strategic Recycled Water Plan to complement the 1992
Recycled Water Master Plan
City of Palo Alto Page 7
Determine the need and timing for appropriate groundwater recharge and
storage of purified water, based on modelling of the San Francisquito Creek
cone
Determine best method of brine disposal and management to allow for the
addition of advanced recycled water treatment processes to the RWQCP’s
current treatment plant
Develop RWQCP regulations and guidelines for the use and management of
recycled water and purified water
Serve as the principal point-of-contact for Partner Agencies to secure new
or modified Recyled Water Service and determine amounts and timing of
needs
Serve as Public Health and Water Board Compliance Officer for water re-
use programs, including inspection programs and cross-connection
prevention programs
Develop and manage Infrastrucutre Management System (IMS) for the
Recycled Water wholesale water treatment and distribution system; track
and manage system repairs and upgrades
Develop Nutrient Credits and Offsets for Recycled Water Program
Coordinate expanded water use and water quality reporting and
monitoring with regulatory agencies, partner agencies, users, site
supervisors, and customers.
Manage expanded recycled water system maintenance and utility locating
services.The new Senior Engineer position would be funded partially by the
partner agences to the RWQCP, since it is a requirement in our discharge permit
to have a recycled water program. Therefore Palo Alto will only fund one third of
the Senior Engineer Position which costs approximately $220,000. The projects
that the Senior Engineer will manage will also be funded through cost-sharing
agreements with the SCVWD, grants and state revolving funds.
Policy Implications
Continuing the exploration of expanding recycled water is consistent with Council
policy. The Recycled Water Program is consistent with the Council-adopted Water
Integrated Resource Plan Guideline 3: “Actively participate in development of cost
effective regional recycled water plans.” The project is consistent with Council
direction to reduce imported water supplies and limit or reduce diversions from
the Tuolomne River.
City of Palo Alto Page 8
Council’s Sustainability Policy supports the development of recycled water,
specifically in the Policy’s statement to “reduce resource use and pollution in a
cost-effective manner while striving to protect and enhance the quality of the air,
water, land and other natural resources.”
The City’s Comprehensive Plan contains Natural Environment Goal N-4: Water
resources are prudently managed to sustain plant and animal life, support urban
activities and protect public health and safety. Specifically, Program N-26
addresses the use of recycled water: implement incentives for the use of drought-
tolerant landscaping and recycled water for landscape irrigation.
Environmental Review
Environmental Impact Report for Phase III of the recycled water pipeline project
was approved in September 2015. Future Environmental Review will be required
if the expanded recycled water pipeline is constructed.
City of Palo Alto | City Clerk's Office | 2/22/2017 11:56 AM
1
Brettle, Jessica
From:Daniel Garber <dan@fgy-arch.com>
Sent:Friday, February 17, 2017 6:42 PM
To:Council, City
Cc:Keith Bennett; Rita Vrhel; Esther Nigenda
Subject:Broad Area v Localized Dewatering
Attachments:170306 Broad Area v Localized Dewatering (6).pdf; Secant Wall .mp4
Dear Council Members-
Attached is a pdf showing the conceptual differences between Broad Area Dewatering and Localized Dewatering strategies that utilize cutoff walls.
Although there are several ways to create a cutoff wall, the mostly like one to be utilized in Palo Alto are cutoff walls made using the secant shoring technique. (Shoring is the term used to describe the holding back of the earth.) In this solution the cutoff wall is created by drilling a sequential series of holes to form a below grade wall. In this process, the earth isn’t removed in the drilling process, rather the earth is mixed with a weak cement or expansive clay to create the wall.
I've recently had conversations with American Drilling's subcontractor Daedalus Engineering who designs the secant walls they build. I have learned that the only data that they need to design a secant wall that allows the dewatering of a localized area, is the same analysis of the soil
borings that is contained in the standard geotech report that the City currently requires (not the "enhanced" geotech report the City is
considering requiring for projects that use broad area dewatering methods).
While the engineer is happy to receive as much information as they can get, they don't need, for example, additional CPTesting to design the
secant wall. This is good news in that it returns the cost for doing a Geotech Report to support a localized dewatering strategy to what it is today.
If monitoring the level of the groundwater is done, two additional costs are required. The first is for acquiring a permit from the County for a well (~400 $/well). The borings that the geotech does routinely do not require permits because they are capped right after the borings have been completed. The second cost is for measuring the level of the groundwater. This is done by hand (dropping a weighted measuring tape) or by sliding a piezometer into the well, either accomplishes the same thing.
I’m expecting to do two projects this year that will utilize a secant cutoff wall. And I’ll be measuring the groundwater level to establish how
effective localized dewatering strategies are in reducing groundwater extraction and what, if any, impacts cutoff walls have on groundwater
flow. Depending on the outcomes of these learnings, the need to monitor the groundwater of future projects that utilize cutoff walls may not
be necessary.
As I reported at the PSC Meeting in December, I’m expecting that the additional cost to build a secant wall to be about 25 to 35% more than utilizing Broad Area Dewatering solutions. However, utilizing a secant wall strategy reduces this added cost by 1) being built in approximately half the time that building the shoring for Broad Area Dewatering requires, 2) it requires fewer trades to be involved in the excavation and shoring compared to what Broad Area Dewatering requires, and although it doesn't directly relate to cost it allows the homeowner to build a basement anytime during the year. The homeowner isn't restricted to just the non-rainy season to build because the
City of Palo Alto | City Clerk's Office | 2/22/2017 11:56 AM
2
City's storm drain system isn't burdened by the large amounts of water that results from a project that utilizes Broad Area dewatering methods.
Thus, localized dewatering strategies adds flexibility to a homeowner’s construction schedule, adds only a very small percent to the overall cost of any new house and importantly avoids removing millions of gallons of water from our underground aquifer.
In addition to the attached pdf document, there is also a link to a small video of the actual soil mixing that is done to create a secant wall.
FYI, I have shared this information with Public Works, in addition to you.
best,
-dan
Daniel Garber, FAIA
Fergus Garber Young Architects
Conserving Palo Alto’s
Ground Water
Broad Area versus Localized Dewatering Strategies
March 6, 2017
Daniel Garber
Save Palo Alto’s Ground Water
February 17, 2017 v6
The Potential Amount of Water that can be kept
from going down the City Storm Drain System
No discharge may be needed with
percolation, trucking and other use
February 17, 2017 v6 Save Palo Alto’s Ground Water Page 4 of 6
Secant Cutoff Wall Concept
METHODOLOGY
1. Drill & Mix Concrete into Soil to Create Secant Wall in Place
2. Excavate to Water, Remove Water From Interior Only
3. Excavate to Basement & Scrape Secant Wall Flat
4. Pour Temp Slab & Waterproof
5.Pour Final Slab & Wall
February 17, 2017 v6 Save Palo Alto’s Ground Water Page 5 of 6
February 17, 2017 v6 Save Palo Alto’s Ground Water
Photos of Secant Cutoff Wall Construction
Page 6 of 6
City of Palo Alto | City Clerk's Office | 2/22/2017 8:20 AM
1
Brettle, Jessica
From:Rita Vrhel <ritavrhel@sbcglobal.net>
Sent:Saturday, February 18, 2017 8:32 AM
To:Keith Bennett; Daniel Garber; Council, City
Cc:Esther Nigenda
Subject:Re: Broad Area v Localized Dewatering
Hi All.... thank you Dan... yes Keith please send as we want everyone to read the document.
Rita C. Vrhel, RN, BSN, CCM
Medical Case Management
Phone: 650-325-2298
Fax: 650-326-9451
On Friday, February 17, 2017 8:26 PM, Keith Bennett <pagroundwater@luxsci.net> wrote:
Dan,
Thank you for this and sending it to Public Works as well.
Should I forward it to Council Members' "personal" e-mail addresses. I recall that at least some
Council members preferred using their personal addresses for "important" stuff.
Keith
On 2/17/2017 6:42 PM, Daniel Garber wrote:
Dear Council Members-
Attached is a pdf showing the conceptual differences between Broad Area Dewatering and Localized
Dewatering strategies that utilize cutoff walls.
Although there are several ways to create a cutoff wall, the mostly like one to be utilized in Palo Alto are cutoff
walls made using the secant shoring technique. (Shoring is the term used to describe the holding back of the earth.) In this solution the cutoff wall is created by drilling a sequential series of holes to form a below grade wall. In this process, the earth isn’t removed in the drilling process, rather the earth is mixed with a weak cement or expansive clay to create the wall.
--
Keith Bennett
http://savepaloaltosgroundwater.org