Bay Area Sewage Systems at Risk as Seas Rise

When sewage spewed out of a shower in a San Francisco home, climate change experts say it may be a sign of things to come as sea levels rise around the Bay. An NBC Bay Area investigation reveals how low-lying sewage treatment plants could fail in the coming years, four of those facilities are vulnerable to flooding within the next decade.

An NBC Bay Area investigation found 30 out of 39 sewage treatment plants located around San Francisco Bay Area are at risk of flooding as sea levels rise due to climate change. Four of those plants could flood with as little as 9.84 inches of sea level rise. That’s an amount that state analysts say is a possibility   by 2030.  If and when that happens, toilets won’t flush, and in some cases, sewage could back up into homes, whether residents live in the hills or along the coast. 

Sewage treatment plants in the San Francisco Bay Area were built on low lying areas along the bay so that wastewater from homes could flow downhill to the facilities using nature’s gravity rather than more expensive machine-driven pumping stations.

“There is a lot of vulnerability of these systems and we really need to start considering them and how we might adapt to future sea level rise,” said Dr. Michelle Hummel, lead author of a UC Berkeley study that analyzed the sewage plants.  “Even if your home itself is not flooding, you could lose access and wastewater service. So, there's a lot of potential impacts that we'll see as an entire region. And it won't just be restricted to folks who live right along the shoreline.”

“The goal of this study was to just highlight the magnitude of this potential threat. And most of us don't think about wastewater on a daily basis when we flush out toilets,” Dr. Hummel said.

NBC Bay Area’s Investigative Unit reviewed data from both the UC Berkeley study and from another independent study conducted by the Bay Area Clean Water Agencies. The combined data show that 30 out of 39 Bay Area sewage plants are at risk of failing as sea levels rise.  The map below shows the water level at which each plant is expected to flood.  

Sea Level Rise Risk at Bay Area Sewage Treatment Plants

Thirty Bay Area sewage treatment plants could be impacted by sea level rise, according to an analysis by NBC Bay Area's Investigative Unit. Together, those 30 facilities serve 6,132,646 people.

Source: Bay Area Clean Water Agencies and UC Berkeley
Map: Sean Myers/NBC Bay Area


“The level of the bay will rise,” said Zach Wasserman, Chairman of the Bay Conservation and Development Commission (BCDC).  “If we do not start acting, do not start figuring out very specifically the ways that we can adapt to this and how we’re going to pay for it,” said Wasserman, “then life in the Bay Area will look and feel very different that it does today. And even people in the hills who will not be directly affected by rising waters will be indirectly affected by it because their transportation systems will be disrupted and the level of groundwater will increase, which could easily make it difficult to flush their toilets.”  

Len Materman agrees.

Materman is C-E-O of “One Shoreline” in San Mateo, also known as the San Mateo County Flood and Sea Level Rise Resiliency District, an agency dedicated to combating rising waters across the Bay Area.

Materman says everyone living in this region, no matter their address, will be affected by rising sea levels.

“It’s (local water treatment plants and infrastructure) at risk. And it's at greater risk as time goes on with sea level rise,” Materman said. “Even if you live in the hills, I mean, if you're in Hillsboro or Woodside or whatnot, you depend on (the plant.) If you flush your toilet you depend on a functioning water treatment plant.”


For an example how that can affect daily life look no further than the story of Sara and Peter Glover.

During a heavy rainstorm, the Glovers suddenly found themselves knee deep in sewage. “The sewage was coming up out of this bathroom,” said Sarah Glover, pointing to a shower on the ground floor of her home in San Francisco’s West Portal neighborhood.   They lost the first floor of their home to the sewage backup, even though they live miles away from the water.  “We’ve lived here for twenty-five years and had no problems,” said Peter Glover, “then in the span of the last, you know, five years, it happened twice.  “Our garbage cans were in the garage. The water was so high they were floating,” said Peter, “I couldn't find my boots because they were underwater. So, the only thing I could grab to remotely even cover my feet with some safety were crocs. And, you know, that's basically walking barefoot through the sewage.”  Repairs to the home cost the Glovers $90-thousand dollars. Even though insurance covered the damage, they say they never recovered from the shock - and the stench. "The odor was horrific," said Sarah Glover. 


Dozens of other neighboring homes in West Portal flooded during that heavy rainstorm in December of 2019 because their sewer pipes aren’t wide enough to accommodate rain runoff and sewage, which share the same path to the Bay.  But as sea levels rise, experts say this same scenario could play out across the Bay Area. 

Without accounting for storms, King Tides and other weather events, the State of California predicts seas will likely rise about half a foot by 2030.  In what scientists say is an extreme scenario - sea level could increase by one foot by 2030.  By the middle of this century, the low figure is 1.1 feet, with an extreme high of nearly three feet. 

One reason for concern that experts point to is what happening to the waters in the Arctic.  “The temperatures in the Arctic are warming up three times faster than they’re warming up in the rest of the planet,” said Dr. Mayra Oyola, an atmospheric scientist for NASA.  In the past decade, NASA and the European Space Agency launched satellites to accurately measure sea levels.  Their data shows a potential for seas to rise as much as eight feet by the end of the century.  “Obviously this is of concern if we’re thinking about people living near the coast,” said Dr. Oyola.

Of the 30 sewage treatment plants at risk in the Bay Area, The Investigative Unit identified four plants, serving 390,736 people, that are most at risk:  Palo Alto, Paradise Cove in Tiburon, San Mateo and Benicia.  Because of their location and height data modeling shows those treatment plants could flood within a decade if scientist’s worst predictions come true.  If seas rise 20 inches, which some models say could happen by 2040, Silicon Valley Clean Water in Redwood City ad Alvarado Wastewater Treatment Plant in Union City are also at high risk.

“There needs to be some big picture thinking,” said Jim McGrath, Chair of the San Francisco Bay Regional Waterboard.  “You’re going to have to think about, okay, are we going to have to reconstruct some of these facilities as force managers, which means you pump them rather than go by gravity, which is more expensive to operate, certainly very expensive and disruptive.”  

Over the next 6 to 9 months, the Waterboard will ask all the sewage treatment plants in the Bay Area to submit their plans to protect their facilities from flooding.  The agency will review the answers they receive, prioritize the plants based on risk, and work with them on potential solutions.  

After sewage caused 90 thousand dollars’ worth of damage to her house, Sarah Glover worries about both her and her neighbors’ future.

“Until the city and the state and the country take climate change seriously,” Glover said, “and I'm hopeful as we move forward that they are (taking it seriously), we’re going to continually be in this position - and it’s a shame, especially in a country with all these resources.”

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