Originally published on July 30, 2025 by the San Mateo Daily Journal and written by Holly Rusch
The threat of groundwater rise is posing increasing threats to coastal communities and infrastructure, U.S. Rep. Kevin Mullin, D-South San Francisco, warned at a press conference introducing legislation that would map, forecast and study the phenomenon and develop mitigation strategies.
“We know that 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,” he said at the press conference July 29. “There is groundwater under our feet, and as the ocean moves inland, it’s pushing more and more water up.”
Amidst Trump administration attacks on climate science and environmental agencies, Mullin is focused on making the bipartisan legislation — co-authored by Rep. Andrew Garbarino, R-N.Y.— as tangible and practical as possible.
“Climate change gets tossed into a partisan bucket, even though we all know that the science exists, but we’re talking about infrastructure. We’re talking about economic impacts, and clearly there are blue states and red states impacted by what we’re talking about here today,” he said.
Groundwater rise is a more subtle and relatively understudied aspect of climate change where water slowly infiltrates soil and ultimately rises to the surface.
As sea levels continue to rise and storms become more severe, millions of people and trillions of dollars in infrastructure and property are at risk from rising groundwater, which can worsen flooding, corrode sewer pipes and spread toxic chemicals, Mullin said.
Because the possibility of such risks need more study for communities to properly protect against them, Mullin’s legislation — dubbed the Groundwater Rise and Infrastructure Preparedness Act — would direct the U.S. Geological Survey to map future groundwater rise and its public health risks.
Areas like the Oyster Point Marina in South San Francisco, where the press conference was held, are vulnerable to the phenomenon, which could extend up to 3 miles inland, OneShoreline CEO Len Materman said.
“When we think about these issues of too much water coming over the Bay. It’s not just what’s coming over the shoreline … it actually is a bit more pernicious and subtle, because it goes farther inland, and we can’t, at this point yet, judge that,” he said. “That’s one of the reasons we need this bill.”
OneShoreline, a San Mateo County agency dedicated to addressing sea-level rise, could use the more detailed data generated by USGS to include groundwater threat preparedness in its planning, Materman said.
“Think of it like you’re planning a project to protect the foundation of your home,” he said. “Would you want to use countywide data on soil and aquifers, or data that is specific to your street?” he said. “We need more detailed information to design these remedies for groundwater rise.”
Many communities susceptible to groundwater risks aren’t even aware of the threat, said Sujata Srivastava, chief policy officer for SPUR, a Bay Area research and urban planning association. New research shows that East Palo Alto, for example, has more than 50 contaminated sites — 30 of which are within areas where groundwater is only 6 feet from the surface.
“These same vulnerabilities are common in many low-lying Bayshore communities,” she said. “A major problem is that many communities are unaware of their risk.”
The actionable plans for climate resilience that legislation like Mullin’s could facilitate is a necessity for Bayshore communities, including for South San Francisco, Mayor Eddie Flores said.
“It fills the knowledge gaps, directs the research and empowers local governments like South San Francisco to understand the threat and respond with precision and with purpose. We cannot protect what we don’t fully understand,” he said.