Radiation is normal at Cesar Chavez Park, but it’s a different story underground, tests show

Cesar Chavez Park sits atop a former municipal landfill. Credit: Phil Rowntree

Radiation testing of Cesar Chavez Park ordered by regional water regulators has found that bird watchers, morning walkers and dogs digging in the dirt have no cause for worry. 

“All radiological activity detected at the ground surface and shallow subsurface is equal to or lower than typical background radiation levels expected in the ambient environment,” according to a report released Monday outlining the results of gamma-ray drone tests conducted this fall by UC Berkeley nuclear engineering experts. 

But underground the landfill-turned-park, it’s a somewhat different story.

Tests of groundwater and leachate — liquids between 6 to 34 feet underground formed when rainwater filters through landfill — revealed higher-than-usual levels of radium-226, a radioactive metal, according to the report, which found four types of radionuclides in the city’s monitoring wells. 

Groundwater and leachate wells are secured with locks, lids and caps. While the wells are not publicly accessible, there could be a danger for workers. 

“Contractors and maintenance personnel who come into contact with subsurface liquids at the site should now take additional precautions to prevent unnecessary exposure to radiation,” reads the report. Chronic exposure to high levels of radium can increase the risk of bone, liver or breast cancer, according to the Environmental Protection Agency website.

The liquid samples were collected by SCS Engineers, which authored the city-commissioned report, and sent to labs in Pittsburg, California and St. Louis, Missouri for analysis. 

The highest levels of radium-226 were discovered in a leachate monitoring well on the northwestern quadrant of the park, according to the report. The sample taken from that well measured 226 picocuries per liter (a unit of measurement for radioactivity in air) — far exceeding the EPA’s limit of 5 picocuries per liter for drinking water. The highest level of radium-226 found in a groundwater monitoring well was 88.8 picocuries per liter. 

But Kai Vetter, a UC Berkeley nuclear engineering professor who specializes in radiation detection and aided with the drone survey, wrote in an email that these levels shouldn’t cause much concern for the park’s casual visitors. (UC Berkeley offered its drone-testing services at no cost to the city.)

“We should not forget that Ra-226 is naturally occurring everywhere and in every object in some quantities,” Vetter wrote. 

Soil, for example, can contain concentrations 10 to 100 times higher than what the city found in the liquids samples, according to Vetter. Even if the leachate were to leak into groundwater or flow into the Bay, it would be “substantially diluted before it will enter the drinking water path,” he wrote.

Put another way, if you were to hypothetically procure heavy construction equipment and dig a massive hole in the former landfill or break into a leachate monitoring well and find water there, it’s a good idea to not drink it.

City manager Paul Buddenhagen struck a note of calm in a Dec. 30 memo to the Berkeley City Council sharing the report. 

“Given these results, public access to Cesar Chavez Park has been and continues to be safe,” Buddenhagen wrote. “The City will continue its due diligence and collaboration with the regulators to ensure all environmental concerns in the park are addressed.”

In January 2024, the water board ordered the city to test for the presence of radioactive material in the park after archival documents emerged showing that the now-defunct Stauffer Chemical Company may have dumped 11,100 pounds of potentially toxic industrial waste there in the 1960s and ’70s when it was still a municipal dump. The city closed the landfill in the 1980s, covered it with soil and thick clay, and in the early 1990s reopened it as Cesar Chavez Park. In a July letter to the water board, the city reiterated that it was not previously aware of the potential presence of radioactive material at the site. 

The Blair Southern Pacific Landfill in Richmond, photographed in November 1957. The site, which accepted hazardous waste from the Stauffer Chemical Company’s Richmond plant, was operated as a landfill between the 1950s and 1980s and abandoned in 1980s and 1990s, according to the DTSC. Radioactive material and pesticides have recently been detected at the site, prompting the water board to order the cities of Berkeley and Albany test soil and water in their former Bay landfills — which also reportedly took in waste from Stauffer’s Richmond plant — for similar compounds. Credit: DTSC

Testing was also ordered at the Albany Bulb, which also accepted waste from Stauffer’s Richmond plant. Elevated radiation levels were discovered at the Albany Bulb, though not so high as to pose much risk to the public. While elevated radiation levels were found in 10 areas of Albany Bulb, you’d need to stand on a hot spot for 20 hours to absorb the amount of radiation you’d get from a single dental x-ray, the Mercury News reported. 

Berkeley is planning follow-up tests of the radionuclides detected in liquids deep underground at Cesar Chavez Park, but is awaiting further guidance from the water board, city spokesperson Seung Lee wrote in an email. In the coming days, the city plans to share public updates about the test results on its capital projects webpage. 

The water board did not immediately respond to Berkeleyside’s questions about a timeline for the follow-up testing. 

The water board also ordered the city to test for pesticides; none were detected, according to the report. 

Background radiation is present everywhere

UC Berkeley nuclear engineering experts fly a drone above Cesar Chavez Park on Oct. 2, 2024. Credit: Iris Kwok

Background radiation naturally occurs in the environment. It’s present in dirt, rocks, food and even in our bones. 

The drone survey — in which a highly sensitive radiation detection system was flown over the park to identify radiation hotspots — found higher radiation levels above the park’s gravel roads than elsewhere in the park. 

That’s normal, according to Vetter, since gravel, paved and concrete roads contain a mix of materials from different areas and as a result have varied amounts of radioactivity depending on the origin. 

“There should be no concern about these differences,” Vetter said. The difference in radiation levels between the gravel roads and the rest of the park was very small — similar, he said, to the difference between the white and the black sand on the beaches of Half Moon Bay, which have different geological origins.