The California Department of Toxic Substances Control (DTSC) has required that the effects of chemicals of concern and depleted uranium at the former munitions plant at Aerojet in Chino Hills be included in a cancer risk calculation.
Aerojet manufactured and tested explosives and chemical warfare agents from 1954 to 1995 at the end of Woodview Road, south of Peyton Drive, under government contracts.
The site has been undergoing cleanup under DTSC oversight since 1997.
The city of Chino Hills asked for a health and ecological risk assessment after residents expressed concerns during a community meeting in 2016.
Russ Edmonton, spokesperson for the DTSC, said the risk must be addressed in the report because there has not been a site-wide comprehensive calculation of cancer risk for the depleted uranium.
He also said the radiologic health branch of the California Department of Public Health would be involved in the calculation of radiation risk.
After 1974, operations involved research, development and testing of armor-piercing incendiary projectiles composed of depleted uranium.
Aerojet tested depleted uranium projectiles by firing them into target plates and sand to establish performance.
The 800-acre site consisted of 400 acres of Aerojet land, and another 400 acres of privately-owned land leased as a buffer zone. In the 2000s, Aerojet purchased the 180-acre McDermont Ranch property, bringing the total property it owns to 580 acres.
The radiologic health branch of the California Department of Public Health, then under the name of the Department of Health Services, provided oversight of the removal of more than 3,000 tons of soil containing depleted uranium in 19 areas of the site in the late 1990s.
The DTSC concluded in a 2004 report that depleted uranium levels in the soil, surface water and groundwater were within acceptable levels for unrestricted use, including residential.
Additional water samplings have been taken and found to be below California and U.S. Environmental Protection Agency maximum contaminant levels for drinking water, according to the DTSC.
Scott Goulart, senior director of environmental remediation for Aerojet, said the cleanup occurred where depleted uranium and chemicals of concern were present but the DTSC is now asking for a comprehensive risk assessment of the entire property.
He said Aerojet submitted a draft workplan which demonstrates how Aerojet will undertake the assessment, and the DTSC is currently reviewing it.
The workplan was produced by Wood Environment & Infrastructure Solutions, a company that has produced numerous technical reports for Aerojet over the decades.
Mr. Goulart said Aerojet will follow U.S. Environmental Protection Agency guidelines for the health risk assessments.
The top three chemicals of concern include the explosive chemicals RDX and HMX, and perchlorate, a chemical used in the production of rocket fuel, missiles and explosives.
These were removed 10 years ago and screening assessments demonstrated that residual concentrations did not pose a risk to human health, according to DTSC.
The DTSC will not release the property for unrestricted use unless the requirements of the health risk assessment for unrestricted land use are met, according to a DTSC document released after the 2016 community meeting in Chino Hills.
“The current zoning allows for rural residential and Aerojet has stated it wishes to remediate the site to allow for future use without DTSC-mandated restrictions,” according to the document. “If homes are developed on the property after DTSC has cleared the site for future use, this would be done through an agreement between the property owner and the City of Chino Hills.”
Aerojet submitted a plan called a “corrective measures study” about five years ago which stated that Aerojet is cleaning the site to a level that would allow unrestricted property use that could include a cemetery and/or residential-commercial uses. Houses could be built in the northwestern portion of Aerojet that abuts Vellano and a cemetery could be located in another area, according to the study.
The City of Chino Hills has the final authority on the zoning and ultimate use of the land.