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Low-lying communities surrounding the San Francisco Bay have been impacted by flooding for years, however sea-level rise and the resulting groundwater rise will exacerbate the region’s flooding challenges.
Last month the nonprofit public policy organization, San Francisco Bay Area Planning and Urban Research Association (SPUR), put out a report in conjunction with Nuestra Casa, a community organization based in East Palo Alto, examining the major impacts that groundwater rise could have in East Palo Alto.
Research around the response of shallow groundwater to sea-level rise is relatively new, but it is clear that the impacts from rising groundwater compounded with sea-level rise and other environmental hazards will negatively impact the region. The report from SPUR, entitled “Look Out Below,” outlines how this previously unexamined risk is a dire and imminent threat to the Bay Area’s coastal municipalities.
Groundwater is the water that is stored in the soil. As rain water falls, it filters through permeable areas in the ground and moves down to the water table, which is the underground boundary between the saturated area where groundwater sits, and the soil surface. Shallow groundwater sits zero to six feet below the soil surface.
As the sea level rises due to climate change, the salty water from the San Francisco Bay will push the groundwater up through the soil. As sea levels rise, so will the levels of groundwater in the soil. According to data from the California Ocean Protection Council referenced in SPUR’s report, sea levels could rise between one foot and six and a half feet between now and 2100.
A map from SPUR’s “Look Out Below” report shows the current levels of groundwater throughout East Palo Alto. Courtesy SPUR, using data sourced from Pathways Climate Institute and San Francisco Estuary Institute. 
A map from SPUR’s “Look Out Below” report shows the projected levels of groundwater throughout East Palo Alto in a one-foot sea-level rise scenario. Courtesy SPUR, using data sourced from Pathways Climate Institute and San Francisco Estuary Institute. 
A map from SPUR’s “Look Out Below” report shows the projected levels of groundwater throughout East Palo Alto in a two-foot sea-level rise scenario. Courtesy SPUR, using data sourced from Pathways Climate Institute and San Francisco Estuary Institute.
For low-lying coastal communities, this means that inland areas could experience flooding from below as groundwater emerges from the ground before ever experiencing direct flooding from coastal floodwaters overtopping the shoreline.
Because East Palo Alto is situated directly next to the Bay, and is surrounded by wetlands, it is uniquely vulnerable to impacts from groundwater rise. The city already struggles with flooding during winter storms, as it is vulnerable to storm surge and urban stream flooding in the areas near the San Francisquito Creek.
“It’s (East Palo Alto) very low lying, it’s already vulnerable to a lot of climate impacts,” said Sarah Atkinson, the hazard resilience senior policy manager at SPUR, who authored the report. “East Palo Alto and East Palo Alto residents have been experiencing flooding during major storms over the last few years, so we already knew that that was a hazard that the city was paying attention to.”
Impacts of groundwater rise
Groundwater rise, when compounded with sea level rise and extreme storms, such as the ones that the region experienced in early 2023, will worsen flooding. The closer the groundwater sits to the surface of the soil, the less capacity the soil has to absorb rainwater during heavy storm events.
According to the report, “without intervention, rising groundwater levels will make flooding increasingly common in neighborhoods east of Pulgas Avenue. Flooding will make it difficult to move around the neighborhood and access basic needs and services.”
Flooding can affect health by leading to increased rates of growth for mold and fungi, which can negatively affect indoor air quality and contribute to respiratory infections.
One of the most concerning impacts of groundwater rise will be the movement of contaminants and hazardous materials at contaminated industrial sites along the Bay. There are more than 50 contaminated sites in East Palo Alto, mostly concentrated in the northern part of the city which is zoned for industrial uses.
These contaminated sites are known to contain hazardous materials such as lead, mercury, arsenic, pesticides, volatile organic compounds and more. When these contaminants interact with shallow groundwater, they can be dissolved into the water or moved to other locations by the water.
These mobilized contaminants can then enter underground sewage and stormwater systems, or move into creeks and impact nearby residents and wildlife. Low-income communities are often disproportionately exposed to contaminants and pollution, and groundwater rise may exacerbate this issue.
Because the science around groundwater rise impacts is relatively new and evolving rapidly, even hazardous waste sites that have technically been closed and remediated may still be at risk for contaminant mobilization from groundwater rise. According to SPUR’s report, many of the previously employed site remediation strategies “do not effectively address sea level rise” or groundwater rise.
Other impacts of groundwater rise include increased liquefaction risks, where saturated soil behaves like a liquid during earthquakes. Liquefaction during a seismic event can lead to increased damage to a city’s infrastructure, beyond normal earthquake damage. Strategies to mitigate liquefaction are often expensive to implement, and retrofits are often impractical.
Groundwater rise may also damage the city’s aging infrastructure, particularly underground infrastructure, on a more incremental basis.
Sewer, stormwater and drinking water systems are likely to be the infrastructure that is most impacted by groundwater rise, as water infrastructure tends to consist of pipes located underground. Shallow groundwater can degrade these underground pipes faster than expected and stress the infrastructure by destabilizing the soil around it, and due to the soil becoming saltier as the sea level rises.
Shallow groundwater can also infiltrate the systems through weak points and threaten human health. When groundwater enters a sewer system, it can cause something called a sanitary sewer overflow, which can lead to untreated or partially treated sewage flowing into the Bay. Leaks in tap water systems can threaten the availability of safe, clean drinking water in people’s homes.
Challenges posed by EPA utilities landscape
East Palo Alto in particular has a unique utilities landscape, as it is served by three different water providers. One larger system, Veolia, serves approximately 80% of residents, while the other 20% are served by two much smaller providers: Palo Alto Park Mutual Water Company and the O’Connor Tract Co-op Water Company.
According to the report, both of the smaller water providers have previously been cited for safe drinking water violations, and Palo Alto Park Mutual has been identified by the water board as having poorly maintained water infrastructure. Presently, both water systems meet minimum federal drinking water standards.
“That is a really interesting challenge,” said Atkinson. “Those water districts, because they’re so small, it’s harder for them to be able to fund the necessary maintenance that is going to be needed with sea-level and groundwater rise.”
This situation makes East Palo Alto an even more interesting case study for groundwater rise.
“The scientific research that has come out over the last few years has been a little broader and more regionally based,” said Atkinson. “But we really wanted to look at one location and understand what the infrastructure impacts were going to be and also how the politics in the space were going to change how a city should be considering groundwater rise.”
According to the report, local, regional and state planning documents that address sea-level rise and climate change have only recently begun to recognize the risk posed by groundwater rise. Some documents, such as the California State Hazard Mitigation Plan, still fail to include planning and guidance for this risk.
However, San Mateo County in particular has begun including groundwater rise in its hazard planning.
“San Mateo County has a sea level rise and flood resilience special district called OneShoreline,” said Atkinson. “That’s a really exciting governance structure that doesn’t really exist anywhere else. And they are definitely paying attention to groundwater rise.”
Addressing groundwater rise risks
SPUR’s report offers several policy suggestions for cities and policymakers that want to manage and reduce the risk of groundwater rise.
A number of cities along the Peninsula, including East Palo Alto, are in the process of updating their safety elements, which is the part of a city’s general plan that is focused on addressing potential threats such as climate change, seismic activity, extreme heat, flooding and more.
In its policy recommendations, the report’s authors advise that cities require all plans for infrastructure projects to assess the risks of groundwater rise, update guidance for remediation requirements for hazardous waste sites along the shoreline and pursue funding to support groundwater rise research and adaptation planning.
The report also advises cities to consider adopting shallow groundwater rise overlay districts in city plans, which specify design and retrofit requirements in high-hazard areas.
“We wanted to pick policy recommendations that we would be able to take action on as a group, and that we were particularly interested in,” said Atkinson. “We had a lot of conversations about, for example, the recommendation on funding opportunities. … We want to make sure that whatever funding opportunity moves forward doesn’t have a negative impact on the community in terms of higher utility fees or increasing insurance rates.”
She emphasized that SPUR’s policy recommendations were developed with the community in mind, and any future solutions that are implemented need to be developed through conversations with the community.
“Whatever solutions are developed, we really need to be thinking about what are the benefits of those solutions for the community,” she said. “What are potential negative impacts that those solutions could bring and how do you mitigate them?”
Atkinson also said that these policy recommendations are not specific to East Palo Alto.
“We would definitely like to see other jurisdictions take more action on groundwater rise,” she said. “For example, last year when Oakland updated their safety element, we provided public comment on the safety element and they included some of our groundwater rise recommendations in that update.”
Groundwater Rise Coalition
Throughout East Palo Alto, groundwater rise is entering the conversation around environmental justice, and community groups are responding.
Nuestra Casa has launched a community coalition to develop strategies to mitigate the local impacts of groundwater rise and to address concerns related to the contaminated sites throughout the city. The Groundwater Rise Coalition is made up of leaders from Nuestra Casa, Youth United for Community Action, Climate Resilient Communities, Belle Haven Empowered and the Belle Haven Community Development Fund.
Nuestra Casa, in conjunction with SPUR, has also developed groundwater “noticias,” a handout in Spanish and English informing the community of how groundwater may impact their city and their homes.
SPUR and Nuestra Casa plan to continue doing groundwater rise advocacy throughout the region.
“This report is the tip of the iceberg in terms of what we are working on and hoping to move forward on in the next year or two with groundwater rise,” said Atkinson.
Read the full report online at spur.org/publications/spur-report/2024-06-12/look-out-below.
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It would be a real service to the residents of EPA as well as others to publish information about how people can address the water issue In their homes. Examples are 1. install reverse osmosis filters 2. Boil all drinking water 3. Treat drinking water with substance that can kill germs and viruses. I’m sure there are better solutions than I can think up and if not, it’s a vital area for research. EPA is one of thousands of affected communities.