HomeMy WebLinkAbout2003-02-03 City Council (3)TO:
FROM:
DATE:
SUBJECT:
HONORABLE CITY COUNCIL
CITY MANAGER
FEBRUARY 3, 2003
DEPARTMENT: UTILITIES
CMR:122:03
PALO ALTO WATER MAIN DISTRIBUTION SYSTEM FLUSHING
PROGRAM - STATUS REPORT
This is an information report and no Council action is required.
BACKGROUND
Historically, the City of Palo Alto and approximately 85 percent of water utilities in the
United States use main flushing to improve water quality for water customers. Water
utilities may flush distribution mains for a variety of reasons: corrosion control, sediment
removal, taste and odor control, control of color, high turbidity, low chlorine residuals,
bacterio!ogical ~-owths, or as a response to customer complaints. The main objectives of
Palo Alto’s flushing prod’am are to improve water quality, control bacterial ~owth and
remove built-up sediment.
Between calendar years 1990 and 1993, the Palo Alto Water Utility did not perfo~xn an
annual main flushing program because of the drought. During this period, customer
water consumption was also reduced, thereby accelerating sediment build-up in the
mains. During 1992, numerous calls were received complaining about water quality. At
that time, staff took water samples in response to these calls and found that the reduced
water quality was due to the build-up of sediment in the mains. Also, City Fire
Department personnel found more sediment in their equipment from the City’s water
system during 1992. Water Utility Operations staff has flushed mains every year since
1993. Since 1993, staff has not received water qualitycomplaints due to sediment build-
~p in the dist-ribution mains because of the success of the annual water distribution
system flushing program.
9 "Pagelof3CMR:12_:0.~
DISCUSSION
Begimaing March 10, 2003 and continuing tl~rough March 16, 2003, the City’s Water
Utility Operations will open fire hydrants to flush out sediment that has collected in the
mains during the past year.
The water system main flushing map and schedule will be mailed to the City’s water
customers through utility billings and displayed in the Palo Alto Weekly, Palo Alto
Daily, City Internet Home Page, and on the AT & T Broad Band Selwices conm~unity
access channel.
After the main flushing proN-am this year, the Water Utility will change the citywide
flushing pro~am to an on-going unidirectional main flushing prodam. Unidirectional
flushing consists of closing appropriate water system valves to create one-way flow in a
neighborhood water pipe loop and then opening hydrants in a set sequential manner.
This increases the speed of the water flow in the pipes to six feet per second or higher.
These high velocities produce a scouring action in the pipes, removing even the most
stubborn deposits. Unidirectional flushing uses up to 40% less water than conventional
flushing and allows for a better response to localized water quality complaints. Because
of better sediment removal, the effects of unidirectional flushing last much longer.
Additionally, unidirectional flushing will test almost all of the water system valves and
hydrants, identifying those in need of repair or replacement. The Water Utility will use
the new unidirectional flushing prod’am to keep the water mains sediment free year-
round.
The main flushing pro~am change is necessary to prepare the water distribution system
for the San Francisco Public Utility Commission (SFPUC) Hetch Hetchy system
disinfectant change from chlorine to chloramine in December 2003. The use of
chloramines as a disinfectant will reduce the formation of disinfection by-prod~cts in the
distribution system. Sediments that normally accumulate in system pipes could provide a
place for bacteria grow when a chloramine is used as a system disinfectant. A
unidirectional flushing prodam will help to minimize this type of water quality event.
ATTACHMENTS
~00~ Water System Flushing Schedule and Map
CMR:122:03 Page 2 of 3
PREPARED BY: An Le, Romel Antonio, Roger Cwiak, and Scott Bradshaw
DEPARTMENT HEAD:
of Utiliti~
CITY MANAGER APPROVAL:
HARRISON
Assistant City Manager
CMR: 122:03 Page 3 of 3
M
10:00 pm
Sunday
March 16
Friday
March 14
Jesday
11
CI ~-~’ OF PALO ALTO
UTILITIES
The City of Palo Alto Utilities will begin flushing
the water distribution system Monday, March
10, 2003 and will continue through Sunday,
March 16, 2003.
Utilities Operations will open fire hydrants to
flush out sediment that has collected in the
mains during the past year.
Flushing of the mains may cause some slight,
but temporary, reduction in water pressure
and possible water discoloration. Your water
remains absolutely safe for drinking.
We suggest that you refrain from doing laundry
while the water lines are being flushed in your
area. If you live near any area border, please
refrain from doing laundry while the water
lines are being flushed in your area and the
adjacent area.
The amount of water released during the
system flushing does not pose a threat of
flooding. However, if athreat of flooding due to
inclement weather should occur during the
flushing schedule, the flushing operations will
be suspended until further notice.