Despite its best efforts, the city will not be able to offer residents and businesses that suffer repeated flooding and sewer overflows a surefire solution. No matter how much money is spent, public utilities managers said at a meeting last night, a really big storm will still overwhelm the city’s sewer system.

“When it’s filled to capacity, no more water can be entered in to the system,” said San Francisco Public Utilities Commission General Manger Harlan Kelly. “Engineers would love to build a bigger system but we’re talking billions of dollars and tearing up the street…We have to work with the system that we have.”

San Francisco’s sewer system, most of which is about 100 years old, can process some 500 million gallons of water on a rainy day. Serious storms can bring down much more and in any big storm, 15th and Wawona streets, Cayuga Avenue at Glen Park, and 17th and Folsom streets are prone to flooding because the overflow works its way down from the city’s watershed to the bay and pool there as a result of the city’s topography, utilities staff explained.

“This issues is one of those that has been very humbling to me,” said Supervisor David Campos in his remarks at the meeting. “There are limitations in what a governing agency can do [against] nature.”

Nevertheless, utilities manager Stephanie Harrison did present three approaches to mitigating the problem. The first would be to construct a $260 million connecting tunnel from 17th and Folsom streets to a bigger, higher-capacity channel tunnel along the city’s eastern edge.  That would move more water away from affected areas, easing the bottleneck that forms in the city’s topographic basins. The catch? That bigger channel tunnel also doesn’t exist yet, and would cost some $800 million to build.

Another option, Harrison said, would be to simply widen an existing water pipeline under 17th and Folsom to a 17-foot diameter. Collection boxes and other associated underground infrastructure would also have to be expanded. Unlike a new tunnel, which would simply involve an entry point for tunneling equipment, expanding old infrastructure requires opening up streets,  which means traffic snarls, utility interruptions, and higher construction cost – a total of $200 million.

Finally, the city could ask parcel owners for permission to dig out storage tanks under parking lots and other empty spaces to catch some of the stormwater that would otherwise flood the surface. Though it’s the cheapest option in terms of installation, weighing in at just $110 million, staff warned that the tanks would need to be emptied and cleaned of debris after each rainfall.

Putting any of these solutions in place would take between five and nine years, with most timelines for completion ending in 2024. It would take until 2017 for the city to even reach a final decision about which approach to take.

“If we’re going to spend a lot of money, I want to solve a problem” said Harlan Kelly, general manager of the Public Utilities Commission. He and others also cited extensive planning and review processes in place to assure transparency in the use of taxpayer money.

Residents weren’t impressed. 

“We are not asking you to protect us from flooding [at the surface],” said one resident. “We are asking you to fix your sewer system so it doesn’t overflow.” He said the pipes under 17th and Folsom, toward the end of the system, simply need to be made proportional to the combined capacity of upstream pipes.

“It’s a little more complicated than that,” said Kelly.

“I don’t think so,” the resident shot back.

“What a joke,” said Blane Bachelor, a Cayuga Avenue resident. “There’s a section of residents in three districts bearing the brunt of the city’s crap.”

Bachelor is one of the core members of Solutions not Sandbags, a group whose mission is to push the Public Utilities Commission toward major sewer improvements rather than short-term fixes.

The latter are in ample supply – the city encourages residents to elevate their buildings, clean their drains, and purchase flood insurance (though residents objected that flood insurance rarely covers sewage back flow, which has damaged several homes). It also offers a program for reimbursing residents who install back flow preventers, flood barriers and other devices.

At Thursday’s meeting, they announced plans to test interlocking modular flood walls around the southwest corner of 17th and Folsom streets, to keep water from flooding off the streets and into the below-grade yards of Hans Art auto shop and Stable Cafe.  

“Is that the best they could come up with, the barriers?” asked Lisa Dunseth, who has not fallen victim to flooding but is also growing impatient with the city’s lack of major sewer improvements. She arrived at the meeting with a binder full of documents detailing plans to improve the sewer system under 17tha and Folsom streets – from in 1964.

“In 1964, plans were made to fix the system. Now it’s 2015 and we have sewer flooding and now we’re going to have it streaming down our sidewalks instead,” she said.

Malcolm Davis, who owns the building that houses Stable Cafe and works upstairs, said he had been told that a basin under the 17th and Folsom parking lot that is slated to become a city park had been taken off the table. At Thursday’s meeting, it was brought up again.

“Really, if they lowered that piece of land by four feet, it could stop flooding in the area,” Davis said. “It feels like turning a huge ship.”