Castle Air Force Base (6 Areas)

Overview

The former Castle Air Force Base sits on 2,777 acres in Merced, California. It operated from 1941 until closing in 1995. Hazardous waste generated during operations contaminated both soil and groundwater across the base. The site has been on the National Priorities List since 1987 and is divided into six operable units, each targeting a specific area or type of contamination.

More than 140 contaminants have been identified at the site. Soil contamination includes volatile organic compounds such as trichloroethene, tetrachloroethene, and benzene, along with heavy metals like lead, chromium, cadmium, and mercury. Polychlorinated biphenyls (PCBs), pesticides including DDT and dieldrin, and polycyclic aromatic hydrocarbons are also present in soil. Groundwater contains volatile organic compounds, metals such as arsenic and lead, and fuel-related contaminants including gasoline and diesel fuel.

The Air Force is the lead agency for cleanup, with EPA and California providing oversight. Major actions completed include excavating seven landfills, removing lead-contaminated soil from firing and skeet shooting ranges, removing PCB-contaminated soil, and installing impermeable caps over two landfills and the former Fire Training Area 1. Two groundwater pump-and-treat systems are still operating. Soil vapor extraction remedies are complete, and monitoring at Landfill 1 confirms the plume there no longer exceeds cleanup levels. The site achieved sitewide readiness for its anticipated reuse in November 2007, and most of the land has been transferred and redeveloped for uses including Castle Airport, Castle Air Museum, and United States Penitentiary Atwater.

A key area of active work involves per- and polyfluoroalkyl substances (PFAS), specifically perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), released from historic use of firefighting foam. Three nearby residences had PFOS and PFOA levels above the EPA Lifetime Health Advisory of 70 parts per trillion. The Air Force responded by supplying bottled water and installing whole-home granular activated carbon treatment systems at affected homes. A remedial investigation and feasibility study for the PFAS operable unit began in February 2023, with completion estimated between December 2026 and February 2027. The most recent five-year review was completed in March 2024. Physical construction of the broader cleanup is complete, though assessments of human exposure control and groundwater migration control across the entire site are listed as having insufficient data.

Community members can contact the EPA Community Involvement Coordinator. The Administrative Record is available through the Air Force website and at the Merced County Library Central Branch at 2100 O Street, Merced, California 95430.