OUR MISSION: To provide our customers with high-quality, efficient and reliable water, power and sewer services in a manner that values environmental and community interests and sustains the resources entrusted to our care.
525 Golden Gate Avenue, 13th Floor
San Francisco, CA 94102
T 415.554.3155
F 415.554.3161
TTY 415.554.3488
San Francisco Public Utilities Commission
Correspondence Log
October 2, 2023 through October 2, 2023
Date Received From Subject
October 2, 2023 Dave Warner Comparing Design Drought Risk to Sewage Overflow Risk
October 2, 2023
Re: Comparing Design Drought Risk to Sewage Overflow Risk
Dear Commissioners, General Manager Herrera and Assistant General Manager Ritchie,
My understanding is that San Francisco’s sewer system is currently designed with a recurrence interval for a raw sewage overflow event once every five years and that the goal is to increase the recurrence interval to once every 100 years. In an undated SFPUC memo to file regarding the SFPUC’s Long Term Vulnerability Assessment1, the design drought was found to have a recurrence interval of 25,293 years. While the memo pointed out that there was a large uncertainty related to extreme drought events, the lower bounds of the 95% confidence interval was still over 12,000 years.
If I were a San Francisco resident, I would gladly trade off reducing the design drought recurrence interval by an order of magnitude in exchange for lengthening the recurrence interval to 100 years or more for a raw sewage overflow. This trade off could easily be achieved by reducing the design drought by a year, thereby reducing the need for alternative water supplies by 20-25 mgd, which frees up funds for sewer system reliability improvements.
In other words, taking a wholistic view of risks across the SFPUC’s services, the design drought stands out as an excessively over-engineered system in the context of competing needs for SFPUC resources.
In the light of competing needs, please ask staff what an appropriate recurrence interval should be for a drought planning model and what such a model would look like.
Best regards,
Dave Warner
1 The title of the undated memo to file is “Issues that arose during the review of working draft final report and how we agreed to resolve them.” The working draft final report referred to is the Long Term Vulnerability Assessment. The recurrence interval of 25,293 years for the design drought can be found in the table under Issue 2.
OUR MISSION: To provide our customers with high-quality, efficient and reliable water, power and sewer services in a manner that values environmental and community interests and sustains the resources entrusted to our care.
525 Golden Gate Avenue, 13th Floor
San Francisco, CA 94102
T 415.554.3155
F 415.554.3161
TTY 415.554.3488
San Francisco Public Utilities Commission
Form Letter
Please Invest in Solutions to Prevent Harmful Algae Blooms & Fish Kills
Unidentified Senders
October 4, 2023 through October 17, 2023
Date Received City
October 4, 2023 San Francisco, CA
October 10, 2023 Pacifica, CA
October 17, 2023 Newbury Park, CA
From: [email protected] on behalf of [email protected] via San Francisco Baykeeper To: Commission
Subject: Please Invest in Solutions to Prevent Harmful Algae Blooms & Fish Kills Date: Wednesday, October 4, 2023 5:02:05 PM
CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
To: Mayor London Breed
CC: SFPUC General Manager Dennis Herrera, SFPUC Commission, and the San Francisco Board of Supervisors
Dear Mayor Breed,
I urge you to direct San Francisco’s Public Utilities Commission (SFPUC) to aggressively increase the city’s investment in water recycling today. If LA can do it, we can!
Last summer, a large harmful algal bloom has spread across the Bay, leaving unimaginable numbers of dead fish in its wake. We’re still learning about this particular bloom, but what we do know is that San Francisco’s sewage effluent contributes to excessive levels of nutrients in San Francisco Bay that make the Bay fertile territory for the spread of harmful algae blooms.
Water recycling and other wastewater management technologies can help by reducing the volume of polluted discharges into the Bay. In addition, by producing potable supplies, water recycling will reduce San Francisco’s reliance on water diverted from the Tuolumne River, increasing the city’s resilience to climate change effects on water supply.
Other cities have learned the lessons of California’s unpredictable climate and are quickly adopting water recycling to reduce their burden on the ecosystem, while increasing the reliability of their supply. Orange County gets more than 75 percent of its water through its water reuse program. Las Vegas recycles nearly all of its water used indoors. And Los Angeles is on the path to reusing 100 percent of its wastewater by 2035.
But, as San Francisco’s draft Urban Water Management Plan recently revealed, the city
currently has no plans to make recycled water widely
available in the next 25 years. Instead, the city is pursuing multiple expensive and misguided lawsuits so that it can continue to rely, almost exclusively, on the Tuolumne River—one of the state’s most overtapped rivers—for the next several decades. San Francisco and large agribusiness water districts divert four out of every five gallons of water that flow in the Tuolumne River during a typical year.
This overuse has caused the river’s once mighty Chinook Salmon populations to crash. Meanwhile, low freshwater flows contribute to deteriorating water quality—including harmful algae blooms—in the Delta and San Francisco Bay.
I agree with Supervisor Aaron Peskin that “it is time for San Francisco and our sister cities in the nine Bay Area counties to start looking at what kinds of infrastructure investments will need to be made as this becomes, sadly, the new normal.” It’s unacceptable for the city with the nation’s greenest reputation to shirk its responsibilities to conserve California’s precious and unpredictable water supply.
I support increasing river flows to protect San Francisco Bay’s fisheries, water quality, and recreation. The city should do its part to protect the Bay and its rivers—water recycling is a common-sense way to limit the city’s water use, increase the reliability of its supply, and protect the Bay from harmful wastewater treatment plant effluent.
Thank you,
SAN FRANCISCO, CA