castle air force base (6 areas)


Castle, formerly Castle Air Force Base (AFB), is in central California within the San Joaquin Valley in Merced County. The site is approximately 6 miles northwest of Merced, near the communities of Winton (to the northwest) and Atwater (to the southwest). The former Castle AFB covered an area of 2,777 acres comprising runway and airfield operations, industrial areas, housing, recreational facilities, and several noncontiguous parcels of land near the base. The largest noncontiguous parcels were two housing annexes totaling approximately 206 acres, located to the southwest of the main base area. Castle AFB was established on September 20, 1941, as the Merced Army Flying School. The base was listed on the U.S. Environmental Protection Agency (EPA) National Priorities List on November 21, 1987, and the base was closed on September 30, 1995, under the authority of the Defense Authorization Amendments, the Base Closure and Realignment Act of 1988, and the Defense Base Closure and Realignment Act of 1990. From closure through 2006, portions of the property were transferred by deeds or federal transfer documents or were subject to lease agreements. By the end of 2006, the Air Force had completed transfer of all property comprising the former Castle AFB to several public and private entities, including the Federal Bureau of Prisons, Merced County, and the City of Atwater. As of the end of 2014, there were approximately 250 monitoring wells (including inactive extraction wells) within Castle and on nearby properties. In addition to monitoring wells, nine active extraction wells and six active injection wells were associated with Castle groundwater remedial systems. The former Castle AFB also includes two former landfills that are part of a post-closure care program, Landfill 4 (LF-4) (Installation Restoration Program [IRP] Site LF007) and Landfill 5 (LF-5) (IRP Site LF008), as well as a former fire training area that requires cap inspection and maintenance, Fire Training Area 1 (FTA-1) (IRP Site FT001). Inspection and monitoring activities at the closed landfills and FTA-1 and the groundwater remedial system maintenance and monitoring activities are part of ongoing Air Force Installation Restoration Program (IRP) efforts.

Hazardous Ranking Score

38 / 100

A score of 28.5 or higher qualifies a site for the Superfund National Priority List.

Regional Contact

Region 9
Phone: (415) 947-4251

Contact Region



Site Inspection
Preliminary Assessment
Final Listing On NPL

Contaminants & Health Effects

      Endocrine Disrupter
      Reproductive Toxin
      Persistent, bioaccumulative and toxic


        African American
        American Indian and Alaska Native
        Native Hawaiian


        People living
        within a 1 mile radius


        Average Income


        Occupied homes

        Potentially Responsible Parties

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