The Moses Lake Wellfield Contamination site covers about 15 square miles in Moses Lake, Washington. It includes the former Larson Air Force Base, Grant County International Airport, and nearby residential and commercial areas. EPA added it to the National Priorities List in 1992 after trichloroethylene (TCE) was discovered in city water supply wells in 1988. The site was previously known as Moses Lake Wellfield Old Larson AFB-Grant Co. Airport.
Air Force and aircraft industry operations from 1942 to 1965 contaminated soil and groundwater with TCE, an industrial solvent used to clean aircraft and missile parts. Dumps and landfills on the former base also released arsenic, lead, mercury, mineral oils, and polychlorinated biphenyls (PCBs). About 1,000 acres of groundwater are contaminated with TCE across multiple plumes in several aquifers. Limited sampling suggests per- and polyfluoroalkyl substances (PFAS) may also be present in some areas. Both groundwater and soil are affected media.
A remedial investigation started in 1999, and EPA selected a cleanup remedy in 2008 through a Record of Decision. A settlement with Boeing, Lockheed Martin, and the City of Moses Lake was signed in 2011. Completed actions include closing or relocating contaminated wells, providing clean drinking water to affected residents, installing wells into uncontaminated aquifers, removing contaminated soil, and building a groundwater treatment plant near the South Plume. That plant became operational in 2019 and removes TCE by filtering contaminated water through carbon material before releasing it back underground. EPA also runs a private well monitoring program that provides free filtration systems to residents whose wells exceed safe TCE levels.
Current work focuses on investigating twelve potential former dump and landfill areas. Two of those sites need no further cleanup, and work has begun at the South Base Dump. A new remedial investigation started in February 2024, with completion estimated between September and November 2028. Physical construction is not complete, and the site has not been deleted from the National Priorities List. Human exposure and groundwater migration are both classified as insufficient data, meaning assessments cannot yet confirm whether exposures are fully controlled. Long-term groundwater restoration is planned but will take considerable time. EPA completed its most recent five-year review in March 2022, with the next one estimated between March and May 2027.
Community members can access the five-year review report and other public documents through the EPA Superfund site profile system or at the EPA Region 10 Superfund Record Center in Seattle, Washington, at 1200 6th Avenue, Suite 155. Residents can also contact the site's Community Involvement Coordinator or Remedial Project Manager directly with questions. Industrial, commercial, and recreational uses currently operate on site, and EPA's Superfund Redevelopment Program has been working with local stakeholders since 2020 to identify barriers to redevelopment and support future reuse.
