The Wash Rack and Treatment Area at McChord Air Force Base sits in Tacoma, Washington. Aircraft washing operations dating back to 1940 used chemical solvents and discharged runoff into unlined leach pits. Over the decades, nearly 500,000 gallons of hazardous substances were used or disposed of at the site. Those activities contaminated groundwater in an area called the Liquid Waste Disposal Area. The site was added to EPA's National Priorities List (NPL) in July 1987 after investigators found organic contamination and a fuel layer in the groundwater.
Six contaminants were identified in the groundwater: benzene, ethylbenzene, lead, mineral oils, toluene, and xylene (mixed isomers). EPA determined these chemicals posed an unacceptable risk to human health or the environment. The U.S. Air Force, EPA, and the State of Washington signed a Federal Facilities Agreement in 1989 to coordinate cleanup. The original remedy used a passive fuel recovery trench and collection drain. In 1994, that approach was replaced with monitored natural attenuation, which lets contaminants naturally break down over time. Remedy construction ran from 1993 to 1995, and benzene levels have stayed below action levels since then.
The site was deleted from the NPL on September 26, 1996. EPA completed a five-year review in 2004 confirming that cleanup goals were met and the remedy continues to protect human health and the environment. The site reached "Sitewide Ready for Anticipated Reuse" status in August 2010, meaning no unacceptable risks remain for current or expected future land uses. Human exposure is under control, with no unacceptable exposure pathways at this time. However, EPA has noted gaps in available data that prevent a firm conclusion about whether contaminated groundwater migration is fully stabilized. Monitoring continues to track any changes. The Washington State Department of Ecology now oversees ongoing operation, maintenance, and groundwater monitoring.
The base itself merged with Fort Lewis in 2010 to become Joint Base Lewis-McChord, which provides airlift services for troops, cargo, and equipment. The Superfund Redevelopment Program supports productive reuse of the site. Community members or interested parties can contact the EPA Remedial Project Manager or Community Involvement Coordinator for more information, or request a copy of the Administrative Record through the site's Public Information Repository.
