Updated: March 9, 2001 [Next] [Previous] [Site Overview Contents] [Region 9 Waste Home] [Region 9 Home] [Superfund Home] [EPA Home] [Site Info Home] CASTLE EPA Region 9 AIR City: Atwater FORCE County: Merced BASE Other Names: CALIFORNIA EPA ID# CA3570024551 Click here for interactive site area map TABLE OF CONTENTS Click on a category below or scroll down the page. ● Site Description and History ❍ Maps ❍ Images ● Threats and Contaminants ❍ Description ❍ Environmental Data ● Cleanup Approach ❍ Response Action Status ● Environmental Progress ● Potentially Responsible Parties ● Site Documents and Reports ● Community Involvement: Public Meetings, Newsletters, and Fact Sheets ● Site Repositories/Library Sources ● Contacts ● Miscellaneous Information SITE DESCRIPTION AND HISTORY Description: The Castle Air Force Base (CAFB) site comprises 2,777 acres and is located in Atwater, California. The installation originally was used as an aircrew training facility by the Army in 1941. The Strategic Air Command assumed responsibility for the base in 1946. Since the mid-1940s, aircraft maintenance, fuel management, and fire training activities on the base have generated wastes that consist primarily of waste fuels, oils, solvents, and cleaners. Base activities also have generated lesser amounts of paints and plating wastes. The Air Force disposed bulk wastes such as solvents, oils, fuels, and sludges in pits at landfills around the base until 1977. Fuel and waste oils were incinerated by the Air Force during fire training exercises. The Air Force ceased disposal of hazardous waste on site in 1977, and the base was officially closed in 1995. Investigations have been completed or are proceeding at multiple areas of contamination including landfills, discharge areas, chemical disposal areas, fire training areas, fuel spill areas, and polychlorinated biphenyl (PCB) spill areas. Approximately 6,000 people obtain their drinking water from both municipal and private wells located near the site. Site Responsibility: NPL LISTING HISTORY This site is being addressed through Federal Proposed Date: 10/15/84 actions. Final Date: 07/22/87 Deleted Date: THREATS AND CONTAMINANTS Groundwater in the shallow and subshallow aquifers in the Main Base and the North, East, and West Flightline areas is contaminated with trichloroethylene (TCE) and benzene. Additionally, groundwater underlying a residential housing area located adjacent to the southwest portion of the Base is contaminated with cis- 1,2-dichloroethylene (DCE). Soils in the Main Base, the East Sector, and the West Flightline Sectors are contaminated with volatile organic compounds (VOCs) including TCE, toluene, ethyl benzene, and xylene. Future workers and residents could be exposed to contaminants by accidentally ingesting or coming into direct contact with contaminated soil. Because groundwater is used by local farmers to irrigate crops, area residents also could be exposed to airborne concentrations of TCE in dusts, and contaminants bioaccumulated in area produce. CLEANUP APPROACH The groundwater contamination at the site is being addressed in five stages: immediate actions, one interim action concerning the shallow aquifer, and three long-term remedial phases focusing on cleanup of: 1) Disposal Area-4 and Wallace Road; 2) the off-base groundwater and sub- shallow aquifers; and 3) the entire base. The site is divided into three operable units for investigation purposes, including the Comprehensive Basewide (CB) Part 1 (Groundwater), the Source Control Operable Unit (SCOU) (Soil), and the Comprehensive Basewide Part 2 (Basewide Wrap-up). The CB Part 1 incorporates areas previously designated Operable Units 1 and 2. Removal actions have been conducted on approximately sixteen sites with soil contamination to expedite cleanup and property reuse. Response Action Status Immediate Actions: The Air Force installed two deep wells in 1988 to replace TCE contaminated water supplies: one for the City of Atwater and one to meet on-base needs. In 1989, the Air Force also built a granular activated carbon filtration system to treat TCE contaminated groundwater. Prior to the installation of these filters, the Air Force supplied area residents with bottled water. Cleanup Ongoing: The Air Force has constructed four groundwater pump-and- treat systems, including the Operable Unit 1 (OU-1), Operable Unit 2 (OU-2), Phase 2, and Castle Vista systems (completed in July 1994, November 1996, and October 1997, respectively). These systems remove chemicals from contaminated groundwater using either a granular activated carbon filtration system (OU-2, Phase 2, and Castle Vista systems) or an air stripping system (OU- 1 system). Three of the pump-and-treat systems are designed to remediate TCE in the groundwater of the Main Base Plume and one is designed to remediate cis- 1,2-DCE in the groundwater of the Castle Vista Plume. The treated groundwater from all systems is reinjected into the ground. Approximately 1,200 pounds of TCE and 26 pounds of DCE have been removed by the four systems by the four systems to date (November 1999). The cleanup of the Castle Vista Plume in particular is progressing well, although groundwater cleanup in general is a very slow process. In 1999, the Air Force was able to shut off portions of the Castle Vista pump and treat system, including two of six extraction wells and two of eight injection wells. They anticipate meeting the cleanup objectives for this plume within the next five years. Remedy Design: The Air Force will begin construction of the Phase 3 groundwater treatment system in early 2000. The effectiveness of the existing treatment systems in cleaning up the contaminated groundwater was evaluated in 1999 in the Technical and Economic Evaluation Report (TEER). The TEER concluded that expansion of the existing treatment systems was necessary to meet the cleanup objectives outlined in the Comprehensive Basewide Part 1 Record of Decision (ROD) and to expedite the groundwater remediation to reduce costs. Phase 3 will involve the installation of eight additional groundwater extraction wells and eight additional injection wells, and the expansion of the existing Phase 2 pump-and-treat plant by adding another pair of granular activated carbon vessels to remove groundwater contaminants. The Phase 3 Work Plan and Remedial Design were completed in the Fall of 1999. The Phase 3 system is scheduled to be operational by Spring 2000. Site Studies: In 1989, a study was initiated to evaluate the nature and extent of soil contamination at over 200 sites that comprise the Source Control Operable Unit (SCOU) and to determine the most effective methods for addressing the contamination. The investigation for the majority of sites was completed in 1997. The Air Force will undertake further investigation of eleven sites with low level VOC contamination during the Spring of 2000 as part of the "Soil Vapor Extraction (SVE) Decision Study." The SVE Decision Study will employ the use of a new technology to collect data and develop conceptual models of subsurface lithology and contamination for each of the eleven sites. The purpose of the study will be to determine whether contaminant levels are sufficiently high to warrant implementation of SVE, a remedial technology that removes volatile contaminants from soils, at these sites. The cleanup decisions for all SCOU sites will be documented in the two- part SCOU Record of Decision (ROD). Part 1 will address the former landfill sites and sites where no environmental cleanup is necessary; this document will be completed in early 2000 and is further discussed below. Part 2 will address the remainder of SCOU sites, many of which have been determined to pose an unacceptable risk to human health and/or the environment, and is scheduled for completion in 2002 following completion of the SVE Decision Study. Remedy Selected: The Air Force is working to finalize the Source Control Operable Unit (SCOU) Record of Decision (ROD) Part 1, which addresses 120 no further action sites (no cleanup required) and seven landfill sites. Cleanup of the landfills was initiated ahead of the ROD through removal actions conducted during 1997 through 1999. These actions are further detailed below. The ROD is expected to be final in early 2000. Cleanup Ongoing: As the investigation of individual contamination at sites continues, removal actions have been initiated several SCOU sites. The Air Force has constructed six soil vapor extraction (SVE) systems: three to remove petroleum hydrocarbons from soil at Fuel Spill 1 (February 1995) , Fuel Spill 2 (September 1995), and Fire Training Area 1 (November 1996); three to remove TCE from soil at Discharge Area 4 (August 1996), Fire Training Area 1 (November 1996), and Discharge Area 8 (January 1997); and one to remove cis-1,2-DCE from soils at Castle Vista Landfill B (September 1998). The Air Force has permanently shut down the system at Fuel Spill 1 and the site is considered closed. They also are preparing to permanently shut down the systems at Fuel Spill 2, Discharge Area 4, Discharge Area 8, and Castle Vista Landfill B. Contaminant concentrations at these sites have been reduced to levels that are sufficiently protective of human health and the environment. As of November 1999, the Air Force has removed 19 oil/water separators (OWS) and 71 underground storage tanks which previously stored fuels and industrial solvents on the Base. Petroleum contaminated soils from former tank and OWS locations were excavated and treated in an on-site land farm treatment cell. Most of the treated soils were then used for constructing the caps for the two on-site landfills, which are discussed below. Cleanup Complete: Landfills: The Air Force has completed remediation of the Base's seven landfills under removal action authority. Landfill 2 and Castle Vista Landfills A and B were excavated during Fall 1997 through Summer 1998; Landfills 1 and 3 were excavated during Summer and Fall 1999. The excavated wastes were determined to be nonhazardous and were disposed in on-site consolidation Landfills 4 and 5. Landfills 4 and 5 have been capped and will be monitored by the Air Force for a minimum of 30 years.