HomeMy WebLinkAboutStaff Report 2310-2173Item No. 3. Page 1 of 4
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Utilities Advisory Commission
Staff Report
From: Dean Batchelor, Director Utilities
Lead Department: Utilities
Meeting Date: December 6, 2023
Staff Report: 2310-2173
TITLE
Staff Requests the Utilities Advisory Commission Recommend the City Council Approve the
Continuation of the Cross-Bore Verification Program
RECOMMENDATION
Staff recommends the Utilities Advisory Commission recommend the City Council approve the
continuation of the Cross-Bore Verification Program to complete the remaining 966 sewer
laterals over the next two years for an estimated $1,352,400
BACKGROUND
A “cross-bore” occurs when a pipe is installed by trenchless technology and inadvertently
penetrates a pre-existing pipe in its path. Cross-bores create an intersection of infrastructure
that compromises the integrity of one or both pipes involved, with potentially severe
consequences. In rare cases, if cross-bores have occurred between sewer laterals and gas lines,
a potentially hazardous situation can be created during sewer lateral cleaning or plumbing work
whereby the sewer cleaning breaks the gas line resulting in the unrestricted release of gas into
the sewer and home. Proactive investigation and prompt repair reduce risk of potentially
hazardous cross-bores.
During 2011, the City of Palo Alto Utilities (CPAU) Department launched a cross-bore verification
program for all active sanitary sewer laterals in the City. The main purpose of the cross-bore
verification program was to help ensure natural gas pipelines or other utilities were not
unintentionally installed through sewer laterals. The first phase of the program (Phase I Cross-
Bore Verification Program) concluded in 2013. During Phase I, the City’s contractor successfully
inspected a total of 7,192 City and private sewer laterals. A total of 26 natural gas cross-bores
were identified during Phase I of the program and CPAU Operations promptly repaired all
identified cross-bores.
During August 2019, the City started the second phase of the cross-bore verification program
(Phase II Cross-Bore Verification Program). Initially, 2,500 sewer laterals were scheduled for
inspection, but the parties terminated the contract during the COVID-19 pandemic because the
original bid price did not include the additional expenses to meet Santa Clara County’s COVID-
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19 safety requirements and the contractor would not execute a contract change order for the
additional expenses. As a result, the City’s contractor inspected 408 of the highest priority City
and private sewer laterals, and no natural gas cross-bores were identified during Phase II of the
program.
The Phase III Cross-Bore Verification Program began during April 2021. Phase III of the program
was completed during September 2022 and the City’s contractor inspected a total of 1,480 City
and private sewer laterals. Only one natural gas cross-bore was observed during Phase III and
CPAU Operations repaired the cross-bore on the same day it was identified.
ANALYSIS
The CPAU cross-bore verification program has been prioritized based on factors that contribute
to greater risk of a cross-bore occurring. For example, gas services installed close to sewer
laterals pose a greater cross-bore risk than those with a greater separation. CPAU staff reviewed
the existing utility asset database to create a list of sewer laterals that could potentially contain
a natural gas cross-bore. The criteria created are as follows.
•The property has a natural gas service that is 1” in diameter and the pipeline material is
polyethylene (PE). The presence of PE pipe is a risk factor because this type of pipe is
typically bored underground whereas other pipe materials were installed using open-
trench construction methods, which do not pose a cross-bore risk.
•The 1” PE gas service was installed by a trenchless operation or identified as “unknown”
installation method. If the PE gas service was installed by open-trench construction, it
does not pose a cross-bore risk.
•The installation date was prior to 2001, if it was installed by a city contractor, or prior to
2011, if it was installed by a city crew, as after these dates CPAU had a cross-bore
inspection program in place.
The above criteria will result in a total of 10,046 out of 17,830 sewer laterals (56%) that were
included in the CPAU cross-bore verification program (Phase I through Phase IV). The cross-bore
inspection was further prioritized to address the type of property served. Other evaluating
factors include the following.
•Whether the property is in a densely populated or “high-consequence” area.
•Whether the gas service has an emergency safety shut-off valve that automatically stops
the uncontrolled release of gas.
•Location of the gas meter: A gas meter at the house poses a greater risk as the gas service
was drilled onto private property and the potential to damage a private sewer lateral is
greater. A curb meter location poses a reduced risk as the gas service is not installed on
private property.
•The proximity of the gas service to the sewer lateral.
As CPAU continues to complete the higher-priority locations, staff expects the number of natural
gas cross-bores to continue to decrease. There are 966 remaining sewer laterals to be inspected
on Phase IV Cross-Bore Verification Program. CPAU has estimated it will take 2 years to complete
these inspections for a total of $1,352,400. The final Phase IV Cross-Bore Verification project has
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not yet been budgeted and staff is seeking concurrence from UAC to continue with the program
despite the reduction in identified natural gas cross-bores observed during Phase II and Phase III.
Although cross-bore inspections in Phases I through III has greatly reduced the likelihood of
discovering a cross-bore within the remaining unverified sewer laterals, the risk has not been
eliminated. A single natural gas cross-bore could have a devastating effect if damaged by a
plumber while clearing a sewer blockage or cleaning a sewer pipe. While inspecting all 10,046
sewer laterals does not guarantee a natural gas cross-bore is not present within a sewer lateral,
the cross-bore verification program will capture and document the inspection of approximately
56% of the sewer laterals in the collection system that meet the criteria for the potential presence
of a natural gas cross-bore.
Staff will continue to assess the number of sewer laterals that meet the criteria for cross-bore
inspection and remove addresses of laterals being inspected internally as some of the gas services
may be replaced through Operations maintenance programs. Historical data, yearly inflation, and
COLA (cost-of-living adjustment) are used to prepare the engineering estimate for the multi-year
contract of the Phase IV Cross-Bore Verification Program. Staff will complete all remaining
inspections of sewer laterals identified as meeting the criteria for potential natural gas cross-
bores within this multi-year contract. Staff estimates there are 966 remaining laterals requiring
inspection.
FISCAL/RESOURCE IMPACT
Currently Phase IV of the cross-bore verification program is not budgeted. Staff estimates it will
require a total of $1,352,400 to complete the remaining higher-priority lateral inspections for all
gas services installed prior to the Department implementing a cross-bore lateral inspection
program. The estimated cost of inspection has increased by 40% due to the estimated cost
aggregated over a two year period and inflation and labor increases over a 4 year span between
bids from Phase III to Phase IV.
Phase
Contract
Duration
(months)
Total Final
Contract
Expenditure
Laterals
Inspected
Gas
Cross-bore
Discovered
Other
Cross-bore
Discovered
Inspections
Performed
per Cross-
bore Found
Cost per
Cross-bore
Avg. Cost
per
Inspection
I 29 $2,946,297 7,192 26 31 126 (0.8%)$51,689 $410
II 9 $245,743 408 0 1 408 (0.2%)$245,743 $512
III 18 $1,251,200 1,480 1 0 1480 (0.07%)$1,251,200 $845
Historical 56 $4,443,240 9,080 27 32 154 $75,309 $485
IV 24 $1,352,400 966 ----$1,400
With 966 sewer laterals to be inspected to complete all legacy gas service installations prior to
the in-line sewer inspection practice and the inherent risk of cross-bores and the devastating
affect a damaged gas pipeline in a sewer pipe can have, staff recommends the UAC recommend
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the City Council approve the continuation of the Cross-Bore Verification Program to complete
the remaining sewer laterals over the next two years, with a contractor, and to include the work
in the operating budget.
For discussion purposes, staff provided three options for completing the cross-bore program,
which are as follows:
•Option 1 – Continue the Cross-Bore Inspection Program and complete the remaining
966 higher-priority sewer laterals over the next 2 years.
•Option 2 – Scale back the Cross-Bore Inspection Program and complete the remaining
966 higher-priority sewer laterals over the next 10 years.
•Option 3 – Discontinue the 3rd-party Cross-Bore Inspection Program based on the
remaining expense and risk reduction achieved to date.
ATTACHMENTS
Attachment A: Presentation
APPROVED By:
Dean Batchelor, Director of Utilities
Staff: Aaron Perkins – Principal Engineer, Utilities
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CROSS-BORE UPDATE
December 06, 2023
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Cross-bore Background
Cross-bore
The unintentional drilling of a new pipeline through an existing
underground pipeline using trenchless drilling method. Cross-bore
between sewer laterals and gas lines are rare but could happen. This
poses a potential hazard during sewer line cleaning or plumbing work.
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3333333
Crossbore Intersection
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Crossbore Inspection
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Grouping of Laterals and Proximity
Group
Proximity Range Between Gas Service and Sewer Lateral
0 ≤ 5'6' ≤ 10'11' ≤ 15'16' ≤ 20'21' ≤Total
1 15 6 9 6 76 112
2 2 1 5 1 40 49
3 59 52 39 40 87 277
4 94 52 54 53 220 473
5 3 0 1 2 13 19
6 9 9 3 2 13 36
Phase IV Inspections
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Phase IV Inspection Data
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Staff Summary
•Staff recommends the UAC recommend the City Council approve the continuation of
the Cross-Bore Verification Program to complete the remaining 966 sewer laterals
over the next two years for an estimated $1,352,400
•Questions?
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Slide Title
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