Lawmakers Push to Map Groundwater Before It Swamps America’s Infrastructure

Updated 2:25 p.m. Tuesday

A Bay Area representative and other federal lawmakers mounted a push on Tuesday for action on groundwater rise, which they warned will worsen flooding across the United States in the decades to come, with the potential to damage critical infrastructure, harm freshwater supplies and spread toxic chemicals into communities.

Rising seas and extreme rainfall press the thin layer of water just below the ground up all along the country’s coasts. In Virginia, sewage stored in septic tanks has already overflowed into homes and spilled onto lawns. Flooding from below could affect the lives of around 7 million people in South Florida. California climate scientists warn that future groundwater rise could move dangerous contaminants into schoolyards.

“Drinking water systems are compromised, roadways are deteriorating and wastewater infrastructure is failing, leading to sewage spills and leaks polluting coastal waterways, posing danger to the public,” Emma Haydocy, senior manager with Surfrider Foundation, said in a statement.

U.S. Reps. Kevin Mullin, D-San Mateo, and Andrew Garbarino, R-N.Y., introduced legislation in June that would set aside $5 million over the next year for the United States Geological Survey to study and map groundwater rise nationally through 2100. The agency would also need to identify priority areas that are at increased risk of flooding.

They held a press conference on Tuesday in South San Francisco in San Mateo County — considered the most at-risk county to sea level rise in California — to push for Congress to advance the legislation, which they dubbed the Groundwater Rise and Infrastructure Preparedness Act of 2025.

“Climate change is going to cause water levels to rise, but there’s more to this challenge, and the truth is it’s mostly hidden from plain sight until it’s too late — there is groundwater under our feet,” Mullin said at Oyster Point Marina along the bay.

Passing the legislation is likely to be difficult, Mullin acknowledged, saying that the Trump administration is ignoring science and partly defunding agencies like the U.S. Environmental Protection Agency and the National Oceanic and Atmospheric Administration that play a pivotal role in tracking warming temperatures.

“We may have a more friendly Congress in a couple of years, but we’re going to keep moving this because we can’t afford to wait,” Mullin said.

Allison Chan, political director with Save the Bay, said the bill is a bold stand in taking the effects of climate change seriously when the federal government is deemphasizing science nationally.

“Flooding from groundwater rise does not have to be a climate impact that our communities suffer from,” Chan said. “Using the right data and resources, we can prevent damage to our homes, schools, and public spaces and prepare people who are at risk instead of spending precious funding on disaster recovery.”

Under the bill, the USGS would study how the phenomenon may affect infrastructure, such as roads, utilities and sewers.

Scientists use an uneven network of wells dug into a complex underground coastal geography to gauge the depth of the water table, which makes forecasting groundwater rise difficult. A mix of urban and rural coastal zones complicates that work.

The scientists would also need to assess public health risks, particularly those associated with the spread of underground pollutants and the contamination of drinking water. For example, in West Oakland, a KQED investigation identified more than 100 sites that could be disturbed by rising groundwater as the bay level rises in the 7-square-mile neighborhood.

USGS scientists would also need to recommend mitigation strategies for communities and create a public-facing website displaying their maps. Within three years, the agency would need to submit a report of its findings to Congress.

In San Mateo County, migrating groundwater already affects private property and public infrastructure, said Len Materman, CEO of the San Mateo County Flood and Sea Level Rise Resiliency District, or OneShoreline.

“To overcome these hurdles and build protection, we need the best tools at our disposal, and in regard to groundwater, we do not yet have this,” Materman said of areas in the county where groundwater is already close to the surface.

Last year, the San Francisco Bay Area Planning and Urban Research Association, or SPUR, partnered with local organizations to publish a study about East Palo Alto’s flood risk due to groundwater rise. They found that migrating water below ground could burst pipes and flood basements and mobilize contaminants from toxic sites.

Since the 1880s, the Pacific Ocean has risen by approximately 8 inches along the West Coast. However, state scientists predict more than a foot of bay rise by 2050 and over 6 feet by the end of the century in the worst-case scenario. But sea level rise won’t just mean water lapping over shorelines. As the bay rises, it will push up groundwater inland.

Groundwater levels during storms have already caused flooding in South San Francisco and are affecting underground infrastructure in the city’s biotech corridor and residential neighborhoods. But to fully understand the impacts, South San Francisco Mayor Eddie Flores said more study is needed.

“We cannot protect what we don’t fully understand,” Flores said. “This legislation ensures we no longer have to choose between preparedness and uncertainty. Climate resilience is not aspirational. It’s operational.”

According to a 2023 study by the San Francisco Estuary Institute, scientists expect rising groundwater levels to occur many years before they reach the surface in Alameda, Marin, San Francisco and San Mateo counties, based on current groundwater levels and global climate projections.

However, the effects of groundwater rise will be visible around the entire rim of the bay. Climate scientists have long warned that the region’s industrial past has resulted in more than 5,000 contaminated sites at risk of groundwater rise, which could spread pollutants into communities.

Industry left sites contaminated with everything from radioactive materials to petroleum, as well as toxic chemicals that can vaporize and enter pipes leading directly to homes — some sites date back to the 19th century.

“It’s like a graveyard,” said Kristina Hill, director of UC Berkeley’s Institute of Urban and Regional Development. “Everything we’ve done in the past is coming up with that groundwater to haunt us in the present.”