The Frontier Fertilizer site covers 8 acres near Davis, California. Pesticide and herbicide storage and mixing in the 1970s and 1980s left soil and groundwater contaminated with multiple chemicals. The site was added to the National Priorities List (NPL) in May 1994, and EPA selected a final cleanup plan in September 2006. Physical construction of the cleanup finished in July 2018. The site remains on the NPL and has not yet achieved sitewide readiness for anticipated reuse.
EPA identified 21 contaminants of concern across soil, groundwater, and air. Key chemicals include four soil fumigant pesticides: 1,2-dibromoethane (EDB), 1,2-dibromo-3-chloropropane (DBCP), 1,2-dichloropropane (DCP), and 1,2,3-trichloropropane (TCP). Carbon tetrachloride, used separately as a grain fumigant, is also present. Other contaminants include chlorinated solvents, pesticides such as aldrin and dieldrin, and volatile organic compounds like benzene and vinyl chloride. The contaminated groundwater plume extends northward past the property line into residential areas.
Cleanup has two main operable units (OUs). OU 1 addressed soil and groundwater using bioremediation, thermal treatment, a monitoring cap, and institutional controls. EPA completed in-situ heating of the source area soil in September 2015, removing 95% of contaminant mass and bringing soil and groundwater in the treated area below cleanup values. No further soil remediation is needed. OU 2 targets the dissolved-phase groundwater plume. Work on OU 2 began in October 2015 and was substantially completed by July 2018. A groundwater extraction and treatment system has run continuously since 1993. EPA upgraded it in 1995 and expanded it in 2017, adding extraction wells and doubling treatment capacity from 80 to 160 gallons per minute. The California Department of Toxic Substances Control (DTSC) now operates and maintains this system, which includes over 100 wells. Solar panels installed between 2007 and 2010 power the treatment system entirely, cutting annual energy costs by $15,000 and reducing carbon dioxide emissions by about 54 metric tons per year.
Human exposure is currently under control, with no unacceptable pathways for people to contact contaminants at this time. However, EPA has noted uncertainty about whether contaminated groundwater migration is fully stabilized. EPA has conducted five-year reviews in 2012, 2017, and September 2022, with the next review estimated between September and November 2027. DTSC monitors groundwater quarterly and publishes reports on results.
Community members can get involved through the Frontier Fertilizer Superfund Oversight Group, the site's community advisory group, led by president Pam Nieberg. For questions about EPA's cleanup work, contact Community Involvement Coordinator David Yogi or Remedial Project Manager Augustin Romero. For questions about the groundwater treatment system, contact DTSC project manager Thomas Tse. Site records are available at the Yolo County Library in Davis and at UC Davis Shields Library.
