Disaster: City Aims to Tap Lake Merced for Water

By Thomas K. Pendergast

Plans for San Francisco’s emergency firefighting water system have been expanded to include drafting water from Lake Merced, which could help the entire west side, especially since Sunset Reservoir water could be claimed by other peninsula water districts.

A seawater pump drawing water from off of Ocean Beach is also being considered. 

Generally known as the Auxiliary Water Supply System (AWSS) it is a pipeline network designed to withstand strong earthquakes and fight the conflagrations that are likely to occur after a 7.8 earthquake, which is roughly the estimated strength of the 1906 temblor. 

[Map source: SFMTA.]

AWSSmap2018 copy

That big shaker killed an estimated 3,000 people, many of them possibly incinerated while trapped in rubble because of 300 broken water mains and 23,000 breaks on service connections in the domestic water supply, and eliminated the water pressure needed to fight the ensuing conflagration.

In the years immediately following that seismic event, the City built the AWSS, a separate high-pressure water system composed of pipelines and seawater pumps designed to withstand a massive earthquake and deliver enough water pressure to fight large fires.

At the time, most of the City’s residents lived on the east side so the original system was only built out, with some expansions, as far west as 12th Avenue in the Richmond District and eventually 19th Avenue in the Sunset District.

In the decades that followed, the City expanded westward but the AWSS system did not follow, leaving about 15 neighborhoods in the western and southern areas vulnerable to a devastating firestorm.

After responsibility for the AWSS was transferred from the SF Fire Department to the SF Public Utilities Commission (SFPUC) by SF Mayor Gavin Newsom in 2010 to address a citywide budget deficit, the commission did explore the idea of fully expanding the AWSS to completely cover the western and southern areas of the City, but balked at its estimated $600 million cost. 

Two bonds have been passed to modernize the city’s water distribution system, but a great deal of the money went into refurbishing and strengthening the transmission pipelines coming from the Hetch Hetchy Reservoir, which cross three major earthquake faults and runs alongside the San Andreas Fault as they come north along the peninsula. Some of that money was used to upgrade and maintain the system here in the City.  

But, exploring AWSS expansion revealed that the current water sources for the system were not enough to supply adequate water pressure for an expanded system to cover the entire City. So, last year the SFPUC proposed constructing a “co-benefits” pipeline to carry water from the Sunset Reservoir and connect to both the domestic water pipelines and proposed high-pressure earthquake-resistant pipelines for use to fight fires after a disaster. This plan depends on a series of automated, mechanized valves to cut the pipelines off from domestic water pipelines, which will likely be broken and, like in 1906, unable to deliver an adequate supply for firefighting.

An expert on emergency water systems, Charles Scawthorn, was asked by SF Supervisor Sandra Lee Fewer during a Feb. 7 meeting of the supervisors’ Government Audit and Oversight Committee if the Sunset Reservoir water would be enough and he said that if the reservoir holds (which has been re-enforced for earthquakes on the northern basin but not the southern basin) then it should have an adequate supply. If it does not, then a redundant supply infrastructure like a pump station at Lake Merced and a seawater pump drawing from Ocean Beach, would make the system more reliable. 

He noted that the AWSS system now in place was designed with multiple sources and multiple layers to back-up the main water tanks and reservoirs. 

Expanding Emergency Response System

The plan has now been revised and includes a pump station at Lake Merced to feed into the system, and a report is being prepared to explore the possibility of adding a seawater pump near Ocean Beach. 

John Scarpulla of the SFPUC said the department is calling the current expansion plans the Potable Westside Emergency Firefighting Water System and, for the time being, it will be only focused on serving the Sunset and Richmond districts. It also will now include four sources of water: the Sunset Reservoir, the Hetch Hetchy transmission line serving that reservoir, Lake Merced and the Hetch Hetchy transmission line at Merced Manor. 

“It’s also being designed with the ability to take in future water sources and extend pieces of pipe … to be adaptable,” Scarpulla said. “It’s being designed with four sources of water now. Additionally we are going to study, in the future, adding a seawater pump station, which could feed into that system. If we go that route, that system would convert from a potable AWSS to a conventional AWSS. So, there’s nothing that doesn’t allow the system to be converted to a conventional AWSS in the future.”

Before the pump station at Lake Merced was included, the initial cost was estimated at $109 million. It is unclear at this time how much more the pump station would add to that cost. 

“Between the Lake Merced pump station, the Sunset pump station and the two transmission mains that will feed in there’s plenty of water to serve both the Sunset and the Richmond,” he said. “We can definitely get enough water to both.” 

Frank Blackburn is a retired SF Fire Department (SFFD) assistant fire chief and he was the project manager of the AWSS extension that brought it as far west as 19th Avenue and to the Outer Mission District in 1986. 

“The mission of the AWSS system and the reason for its construction is for it to survive an earthquake. It has multiple sources of water supply including the Pacific Ocean and San Francisco Bay, which is an inexhaustible amount,” Blackburn said. “(The SFPUC) wants to call it ‘co-benefit.’ It should be a single use, firefighting only, because as you say ‘co-benefit’ then what does that mean? You always compromise the performance and the design, no matter what it is, as soon as you try to do two things, two completely separate operations and they both need all the water available.”

With the current AWSS system, there are no connections to the domestic water supply system. If a break occurs in the AWSS high-pressure lines, the compromised segment can be isolated through the use of automated and mechanized gate valves. Plans being developed for the west side do connect the system to the domestic water pipeline system, however, the SFPUC is counting on the same kind of valves to isolate the high-pressure system from the domestic water supply if needed during an emergency. 

“We engineered this system to assume that there are going to be multiple uses,” Scarpulla said. “There are redundancies on the valves. These are seismically reliant valves, so they are purposefully supposed to function after an earthquake. If they don’t automatically close, you can crank them closed. There’s battery power. There’s all these ways to make sure they work. We’ve designed the system to continue to function in that occurrence.”

Yet Blackburn is not convinced.

“The more complicated you make that system, the chance of it not functioning after a major earthquake is very, very high,” Blackburn said. “Because of the motorized gate valves, every one of those has to be closed off.”

The issue with the seawater pump station is where to locate it along Ocean Beach. The southern part of the beach at Sloat Boulevard and Fort Funston is eroding significantly; however, the northern section adjacent to the Richmond is actually adding sand over time. That is where Blackburn thinks it should go. 

“It would be between Balboa Street and Fulton Street,” he said. “The pump station would be underground. They’ll have a six-foot (wide) concrete tunnel that would go out and the inlet would be beyond the surf line at Ocean Beach, about 120 yards out if it’s deep enough.”

Who Has Water Rights?

Yet another issue has come to light recently. According to both California State Law and the 2009 Water Supply Agreement between the SFPUC and the 27 other water districts fed by the Hetch Hetchy system, this water must be distributed “on an equitable basis throughout the Regional Water System service area following a regional Emergency.” This would include water in the “terminal” reservoirs of the system: Sunset, Merced Manor and University Mound. 

Even if the south basin of the Sunset Reservoir is not compromised by an earthquake, at most San Francisco has about four to five days of drinking water. Nevertheless, SFPUC officials say that is not a problem because reinforced Hetch Hetchy transmission lines would replenish the reservoir within 24 hours. 

But the water transmission lines cross three major earthquake faults and run north along the peninsula right beside the San Andreas Fault. So, there is no guarantee that the system will not fail at some point. Meanwhile, the three terminal reservoirs in San Francisco can “backflow” to various cities along the peninsula and south bay for emergency use. 

It is unknown if this course of action would be required. Most of the cities along the Peninsula that buy water from the SFPUC have their own reservoirs or groundwater wells, and many now receive or if need be they can get water from the Crystal Springs or San Andreas reservoirs. The former has a total of 22.5 billion gallons of water, while the latter has another 6.2 billion gallons of water, far more than the 177 million gallons stored in the Sunset Reservoir. a

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