By Thomas K. Pendergast
Perhaps a dozen or so neighborhoods in the western and southern parts of San Francisco could burn to the ground after a 7.8 magnitude or larger earthquake, because water for firefighting might not be available.
The combination of ruptured water and gas lines, along with potential ignition sources, makes a repeat of the 1906 earthquake disaster possible because much of the damage from that disaster was due to firestorms that swept through the city’s wood-framed buildings, possibly immolating thousands in the process.
One San Francisco supervisor, the Richmond District’s Sandra Lee Fewer, asked the SF Public Utilities Commission (SFPUC) to come up with a study of options for addressing this issue after it offered a previous solution that the SF Fire Depart ment (SFFD) deemed unworkable.
In January, the SFPUC released new recommendations, although they focused mostly on the Richmond and to a lesser extent the Sunset District, for creating an emergency water system that could control a massive conflagration, and for dealing with a potential disaster. Not included in the report, however, was information addressing the fire dangers in the Bayview Heights, Crocker Amazon, Excelsior, Ingleside, Little Hollywood, Mission Terrace, Outer Mission, Sea Cliff, Stonestown and Sunnyside neighborhoods.
Fewer has called for a hearing about the issue at the SF Board of Supervisors’ Government and Oversight Committee on Wednesday, Feb. 7, at 10 a.m., at City Hall, Room 250.
The death toll from the 1906 earthquake is now estimated at about 3,000 people, killed after the city’s water system pipelines sustained more than 300 breaks on water mains and 23,000 breaks on service connections.
The SFFD lost water pressure at the same time that busted gas lines became vulnerable to multiple conflagrations from collapsed buildings and those dynamited to form fire breaks, which ultimately devastated much of the City in a blazing inferno. Only U.S. Navy ships running hoses full of seawater and pumping along Van Ness Avenue and the Embarcadero prevented the fire from spreading even further.
Immediately following the earthquake, city leaders designed and ordered built the Auxiliary Water Supply System (AWSS), a network of pipelines made to withstand a large earthquake and meant exclusively for firefighting, while completely separated from the regular water supply pipelines. This system of extra-robust pipelines would be able to use both fresh water from the city’s reservoirs and tanks, plus an unlimited supply of saltwater as well, to fight fires.
The fresh water supply relies on gravity to send water downhill from the Twin Peaks Reservoir, so it does not need pumping nor is it dependent on PG&E. Two large pumps with independent power sources are used to push saltwater into the AWSS as needed. The pumps can supply up to 330 pounds-per-square-inch (p.s.i.) of pressure and the system was designed to provide high-pressure water for firefighting within 30 minutes of a major earthquake.
In 1986, voters passed a $48 million bond measure to upgrade two saltwater pumps and for several AWSS extensions, including along Portola Drive, Ocean Avenue and Mission Street to create a large loop. The AWSS was also extended along Seventh Avenue, Taraval Street and 19th Avenue. A smaller “loop” goes around the Bay View, in the area of Oakdale, Third and Revere streets, but is deemed a “dead end loop” because of water pressure issues.
According to the new study released by the SFPUC, which focuses on the Richmond District but notes some options for the Sunset District, there are two basic options, with multiple variations of each.
The first option extends the AWSS, which is fed by the Twin Peaks Reservoir and Ashbury and Jones storage tanks, with emergency water available from two saltwater pump stations and two SFFD fireboats.
The AWSS pipeline standards have changed from the original heavy wall cast iron pipe with lead joints, to take advantage of current earthquake resistant pipeline standards, says the SFPUC report, and the SFPUC is in the process of formally adopting new standards, which include material, design and testing requirements, for the AWSS’ pipe, valves, hydrants and other system elements.
Recent AWSS installations have used Earthquake Resistant Ductile Iron Pipe (ERDIP), which is manufactured by Kubota and has been deployed in Japan since 1974. There have been no documented failures in subsequent seismic events, including the 1995 Kobe and 2011 Great East Japan earthquakes.
The second option for an emergency firefighting water supply is the Potable Co-benefits system, which would use the Sunset Reservoir as its primary water provider.
The potable approach utilizes a dual purpose pipeline that is independent from the existing AWSS network. It would be used as a potable water transmission main in normal daily operations, but could be converted to provide a firefighting water supply for greater alarm fires in emergency situations.
Between the two main options, there are 12 variations that the SFPUC considered, with the first seven being variations of extending the AWSS lines:
• Option one includes the addition of an AWSS connection from the south, through a crossover from 19th Avenue in the Sunset District and the Twin Peaks zone;
• Option two includes an additional AWSS pipe in Laurel Heights and 10 connections with several different combinations of AWSS connections considered within and around Laurel Heights, since it is a major thoroughfare;
• Option three provides a similar similar expansion in hydraulic capacity through the Ashbury zone as option two, using a single connection under Geary Boulevard instead of multiple main connections. Though Geary is a major street, the new connection improves the conveyance with a straight alignment and less new pipe length;
• Option four includes the same AWSS layout as option two, but with the removal of a crossover feed from the south;
• Option five includes all elements of option three, except with the crossover pipeline from the south removed;
• Option six uses Lake Merced as a potential water source by installing an inline booster pump at the connection point between the Ingleside pipeline project and Park Merced’s AWSS network. The pump output at this location is modeled at 15,000 gallons per minute, at 250 p.s.i. At the same time, the division gate between the Ingleside Pipeline and Ocean Avenue AWSS is opened to allow a booster pump to deliver water into the Twin Peaks zone.
In order to take full advantage of the additional supply from Park Merced to the Twin Peaks zone, the division gates on both sides of the I-280 freeway should be closed, so that water from Lake Merced does not pass beyond the I-280 freeway. However, this option requires the construction of the Ingleside Project, Lake Merced Pump Station improvements and the Park Merced AWSS mains that are currently planned to be constructed and funded by the Park Merced developer over the next 20 to 30 years;
• Option seven connects the Sunset Reservoir to the AWSS with an inline booster pump. An “air gap” facility would need to be constructed to assure no AWSS water would be capable of entering the potable water system at the Sunset Reservoir.
The remaining five options are Potable Co-benefits plans.
• Options eight through 12 utilize the “potable” alternative to supply water to the Richmond District, with some benefit for the Sunset District.
The potable approach would be used as a water transmission line for normal daily operations, and provide a firefighting water supply under emergency conditions.
The dual purpose pipeline is to be designed to AWSS standards and have seismically actuated control valves on certain connections to the potable system, allowing it to be isolated following an earthquake. The isolated dual-purpose pipeline would be pressurized with the booster pump system to provide higher pressures for firefighting, similar to the AWSS.
The potable pipeline reliability is assumed to be very high since it will be constructed to current AWSS standards.
Because the “source-of-supply” and transmission pipes leading to Sunset Reservoir have been seismically upgraded, the supply reliability is also considered to be high, according to the SFPUC study.
Additional reliability factors could be applied to the other key system features of the potable system, such as pumps and motorized valves.
The SFPUC report assumes equal reliability for each of the potable options even though the options provide different area coverage. The options all include a booster pump station located at the Sunset Reservoir.
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