EPA ID# WAD988466355
EPA Region 10
Grant County
Moses Lake

4th Congressional District

Other Names:
Last Update: June, 2012

Hide details for Site DescriptionSite Description

The Moses Lake Wellfield Contamination site is located about three miles northwest of the city of Moses Lake, Washington, in unincorporated Grant County. The Site encompasses potential source areas around the former Larson Air Force Base, and is currently the home of the Grant County International Airport. Potential source areas are scattered throughout the area, and approximately 1000 acres of groundwater are contaminated with trichloroethylene (TCE). The contamination is the result of operations of the former Larson Air Force Base and industrial activities associated with the aircraft industry. There are multiple potentially contaminated soil waste sites and several groundwater plumes of TCE that pose a threat to human health and the environment. TCE is a solvent used by industries to remove grease. EPA considers TCE highly likely to cause cancer in people. The contaminated groundwater plumes lie beneath and extend south from the former Larson Air Force Base.

The U.S. Air Force used the base for a variety of purposes from 1942 until it was deactivated in 1963. Since 1966, when the base was disbanded and put up for sale, a variety of entities have acquired properties of the former base. The Port of Moses Lake acquired the largest parcel of property for use as the Grant County Airport. Other properties include commercial facilities and residences. The area surrounding the site is residential, agricultural, and commercial.

The groundwater contamination was initially identified in 1988 by the Washington Department of Health during routine sampling of municipal drinking water wells. A number of municipal and private wells have contamination above EPA and state drinking water standards. Two of the contaminated municipal wells were part of a blended system that provides drinking water to approximately 5,000 people. The City of Moses Lake redeveloped their well system soon after the discovery of TCE to obtain clean groundwater from a deeper source. Between 1989 and 1993 the City fixed the three contaminated wells on the former base by deepening the wells. In 2003, EPA and the U.S. Army Corps of Engineers (USACE) completed deepening a groundwater well for a 100-home residential development served by the Skyline Water System. Both of these efforts occurred within the Moses Lake Wellfield Contamination site, and in both cases, clean groundwater was obtained from a deeper source. The Corps and EPA continue to test a representative set of wells (up to 80) at the site. Based on this sampling, five homes have had whole-house filters installed at their wells to remove TCE from the water.

The Remedial Investigation/Feasibility Study (RI/FS) process was completed in 2007. Several TCE groundwater plumes were identified as well as multiple soil contamination areas, some of which are suspected to contain TCE and may contribute to groundwater contamination. EPA issued an Interim Record of Decision for the site cleanup in 2008.

In 2010, EPA and the Army Corps of Engineers signed a cleanup settlement with Boeing, Lockheed Martin, and the City of Moses Lake. Boeing, Lockheed Martin, and City of Moses Lake will pay $3.25 million for cleanup and the federal government will pay $55 million.

Site Responsibility: This site is being addressed through federal actions.

NPL Listing HistoryDates
Proposed Date:07/29/1991
Removed Date:
Withdrawal Date:
Final Date:10/14/1992
Deleted Date:

Hide details for Threats and ContaminantsThreats and Contaminants

Media Affected: Groundwater
Approximately 1000 acres of groundwater are contaminated with TCE. The safe level for TCE in drinking water is set at 5 parts per billion (ppb). The contaminated groundwater at this site contains TCE concentrations above 5 ppb and some areas contain TCE above 80 ppb. Moses Lake municipal drinking water wells were contaminated. The Skyline water system, a private water system with approximately 100 connections, was also contaminated. The Skyline backup well remains contaminated. Direct contact with or ingestion of contaminated groundwater posed a health risk until EPA and USACE recently completed the deeper Skyline well. At this time TCE exposures via groundwater contact, ingestion, and inhalation appear to be controlled for all known groundwater pathways. However, future development could result in new TCE exposures.

Soils - Besides groundwater contamination at the Moses Lake site, there are issues associated with landfills, waste discharge areas, and other potentially hazardous constituent source areas. For example, even though it may not be possible to directly link any specific TCE source area at the former Larson Air Force Base to specific TCE plumes in groundwater, many other hazardous constituents are often located within each source area, so that future development may need to be managed to prevent exposures. Each area where hazardous constituents are located at the site must be considered in this context, and an appropriate remedy selected. The only areas of the site where no further action may be warranted are those where EPA determines hazardous constituents will not pose an unacceptable risk under reasonably anticipated future land-use scenarios.

Hide details for Cleanup ProgressCleanup Progress

Short-Term and Removal Actions: The City of Moses Lake voluntarily closed or relocated contaminated municipal wells to a deeper uncontaminated aquifer soon after TCE was detected. Bottled water was provided to Skyline Water Company users for many years until the new Skyline well was completed in September 2003. Therefore, both City of Moses Lake and Skyline Water Company users are protected from TCE exposure. In 2002 TCE was discovered in a sump and soils at the liquid oxygen facility. The sump and contaminated soils were removed by the USACE under an interim remedial action.

Long-Term Actions: The proposed interim cleanup is expected to cost about $31 million and calls for:
pumping out the most highly contaminated water and treating it to remove TCE;
cleaning up the contaminated soil areas by removing soils contaminated above safe levels;
restoring the groundwater to its highest beneficial use as a drinking water source; and
requiring local land use restrictions such as changes to local ordinances, zoning, and property easements to protect the public from contaminated groundwater and soils.

In June-October 2012, EPA contractors are testing and designing a treatment system to remove TCE from one of the two major groundwater contamination plumes. EPA will also start testing and designing cleanup at two contaminated soil sites.

Groundwater Treatment

Two groundwater TCE plumes begin under the former Larson Air Force Base and spread to the south.

We are starting cleanup at the South Groundwater Plume since it is closer to homes with private wells and we want to clean up the source of this plume.

The South Groundwater Plume starts 150–250 feet underground at the South Base Dump (Site 20) and goes about 1.3 miles south-southwest. TCE levels in this plume range from 88 ppm beneath the dump and down to 5 ppm at the outer edge further south.

We are drilling groundwater monitoring and extraction wells to learn more about the size of the plume and the best way to clean it up. The groundwater treatment system will to pump out the groundwater and filter out the TCE. After we start the groundwater treatment system, we will keep the treatment system going until the groundwater meets EPA’s safe drinking water standard of 5 ppm TCE.

Soil Cleanup

Twelve soil sites on the former base and around the airport were used as dumps and landfills. EPA is starting the investigation and cleanup at two of the soil sites that pose the biggest environmental risk.

The South Base Dump (Site 20) is located in the south corner of the former base. Toxic metals like arsenic, lead, and mercury, plus gasoline, diesel, oil, PCBs, and TCE waste were probably disposed at this dump. We think that the South Groundwater Plume begins at Site 20. EPA will test the soils and groundwater, then design a cleanup to remove all the contamination that exceeds EPA’s safety levels for residential areas.

The Paint Hangar Leach Pit (Site 22) is located near the eastern corner of the airport. Toxic metals like lead, and toxic substances such as PCBs were detected during the initial investigation. EPA will test the soils and groundwater, then design a cleanup to remove all the contamination that exceeds EPA’s safety levels for industrial areas.

Hide details for Regional ContactsRegional Contacts

PHONE NUMBER:509-376-3749
PHONE NUMBER:206-553-6689 or 800-424-4372
Information pertaining to this site is housed at the following location(s):

EPA Moses Lake Superfund web site:

Big Bend Community College Library
7662 Chanute St, Building 1800
Moses Lake, WA 98837-3299
call ahead for hours (509) 793-2350

EPA Region 10 Superfund Records Center
1200 6th Ave, Ste 900
Seattle, WA 98101
call for an appointment (206) 553-4494