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MAP: More Than 5,000 Toxic Sites Along SF Bay Threatened by Rising Groundwater, New Study Finds

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A panoramic view of the North Bay shoreline near Rodeo. In the foreground are oil refinery terminals. Behind them are houses and hills.
Phillips 66's refinery in Rodeo, along the San Pablo Bay, near several open toxic sites that are vulnerable to groundwater rise. (Carlos Avila Gonzalez/The San Francisco Chronicle via Getty Images)

More than 5,200 toxic sites buried along the lip of San Francisco Bay could be impacted by rising groundwater levels over the next century, posing potentially severe risks to human and environmental health, according to a recently released study.

That’s more than 10 times as many potentially at-risk Bay Area sites as had been identified in previous reports. A disproportionate number are located in lower-income communities of color, including in low-lying areas of San Francisco, Richmond, West Oakland and East Palo Alto.

“The higher the social vulnerability, the higher the density of contaminated sites,” said Kristina Hill, director of UC Berkeley’s Institute of Urban and Regional Development, who co-authored the study.

Unlike much lower tallies from the federal and state agencies that oversee these sites, Hill’s study includes 1,480 open sites, which are in the process of being cleaned up or have not yet been cleaned up, as well as an additional 3,817 closed sites where some level of cleanup work may have been conducted, but that may still contain residual contaminants and be vulnerable to rising groundwater.

The map below shows the more than 5,000 open (orange circle) and closed (black square) contaminated sites in the Bay Area that UC Berkeley Institute of Urban and Regional Development researchers identified as being potentially at risk of inundation by rising groundwater over the next century. Open sites include areas where cleanup has yet to begin or is still in progress. Closed sites include areas where cleanup has been completed but may still contain harmful toxins. For more information on each toxic site and the agency overseeing its cleanup, visit either of these searchable databases: Envirostor (from California’s Department of Toxics Control) or GeoTracker (from the state Water Resources Control Board).

Map by Matthew Green/KQED


Sites are contaminated with everything from radioactive materials and small underground petroleum tanks to toxic chemicals that can vaporize into pipes leading directly to homes, Hill said. Some sites date to the 19th century.

“It’s like a graveyard,” Hill said. “Everything we’ve done in the past is coming up with that groundwater to haunt us in the present.”

While other studies have identified toxic sites at risk of coastal flooding due to climate change, this is the first to comprehensively pinpoint areas where rising groundwater is likely to come into contact with contaminants and potentially move them toward both the bay and people’s homes. Twice as much land in the Bay Area could be affected by groundwater rise compared to coastal flooding, according to the new study, which is currently in the process of peer review (a preprint and preliminary data are publicly available).

Hill found that in nearly all Bay Area counties, the impact from rising groundwater along the bay will be more severe than from the more than three feet of sea level that could take place by mid-century. She said additional research is needed to better understand the risks those contaminants pose to human health.

In the study, Hill found that in all but one Bay Area county (Santa Clara County), the impact from rising groundwater along the bay will be more severe than that from rising seas. She said additional research is needed to better understand the risks those contaminants pose to human health.

More on toxic sites

The risk of potential contamination from groundwater rise is notably higher in California as compared to most other states because of its vast coastline and sheer number of vulnerable sites, she noted.

Hill said that rising groundwater — potentially made worse during atmospheric river storms and rising tides — is “already moving contaminants” toward homes and businesses from toxic sites in places like Richmond.

The two state agencies in charge of enforcing cleanup of the sites, Hill said, need “to flip a switch” to the default goal of removing or neutralizing contaminants.

“It’s a solvable problem. But it requires us to dig up the graves,” she said, emphasizing the need to consider rising groundwater levels in future climate adaptation plans.

“The idea is not to run away from these places,” she added. “The idea is to make them safe and healthy again.”

Cleanup of toxic sites can range from digging up contaminants and trucking debris to contained locations, treating toxics directly on-site, or capping the pollutants in the ground with materials like cement to prevent them from leaking. That third option, Hill said, is likely not a good long-term solution because groundwater rise will generally circumvent barriers over time.

The new findings presented in the study are revelatory and underscore the urgency of the situation, said Todd Sax, deputy director of site mitigation and restoration with the California Department of Toxic Substances Control, or DTSC, one of the agencies tasked with holding polluters accountable for cleaning up at-risk contaminated areas.

Sax said his agency has identified about 300 particularly vulnerable toxic sites in the Bay Area and has set the goal of shoring them up to withstand 3.5 feet of sea level rise by 2050 and 6 feet by 2100. On a rolling basis, the agency is beginning to require known polluters to assess the risks posed by sea-level and groundwater rise at those sites and perform the necessary cleanups.

“The bottom line is the polluter will pay for the vulnerability assessment unless the site does not have a responsible party,” Sax said.

But he noted that a site cleanup doesn’t always mean polluters will be required to remove all contamination, even after a vulnerability assessment. He said that sometimes trucking contaminants out of a community can be more harmful to human health and the bay than leaving them in the ground.

“There aren’t any magic bullets to help solve the environmental contamination problem,” he said. “The best we can do is remove or treat the contamination where we can and then to engineer robust solutions that protect public health and the environment into the future.”

Meanwhile, the San Francisco Bay Regional Water Quality Control Board, which oversees cleanup operations in some 1,000 vulnerable toxic sites in the region, has only begun enforcing groundwater rise assessment in a tiny percentage of cleanup plans, said Alec Naugle, the agency’s toxics cleanup division manager.

“We have to act more quickly on the most vulnerable sites,” he said, stressing the need for more caseworkers to manage the cleanups. He said the agency recently began requiring landfill operators to account for groundwater rise.

“The public can understand that this isn’t going ignored,” he said. “It is a sort of a slow-moving train and, at the same time, we need to have eyes on it now because the remedy is going to be costly.”

Naugle and Sax note that the number of toxic sites identified in this study is substantially larger than the number their agencies oversee, due largely to Hill’s inclusion of closed sites, which could pose a lower risk to public health.

Still, both agencies said they are assessing Hill’s data.

“What Dr. Hill’s study points out, is that fundamentally, there’s going to be issues with these sites into the future,” Sax said.



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