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Posted 10/5/2016

Release no. 16-035


SEATTLE – U.S. Army Corps of Engineers’ officials will begin installing six new deep groundwater monitoring wells in mid-October at the Moses Lake Wellfield Superfund site in Moses Lake, Washington.

The new wells will help fill data gaps for groundwater plumes as part of the Environmental Protection Agency’s long-term effort to clean the Superfund site’s contaminated groundwater and soil.

Groundwater contamination is from operations at the old Larson Air Force Base and Grant County Airport, where trichloroethene, or TCE, was used as an industrial solvent for cleaning and stripping aviation parts.  As a result, two TCE-contaminated groundwater plumes are located under the former air base property.

The new monitoring wells will be installed in pairs at three residential locations where workers will drill 200-300 feet in depth.  Site activities including mobilization, drilling, maintenance and demobilization are scheduled to take place from 7 a.m. to 5 p.m., Monday through Saturday with all activities being complete by the end of January 2017. Approximately four weeks of drilling are anticipated at each of the three residential locations.

The Corps took samples from 85 monitoring wells in May and anticipate having results available to the public in early 2017.  Data from both new and existing wells will aid Corps scientists in determining if groundwater plumes are moving, what types of contaminants are present and if conditions have changed.  The EPA will incorporate the information into a groundwater pump-and-treat system it is designing. 

Most residents get their drinking water from the City of Moses Lake or community systems, which are tested regularly to ensure they meet Safe Drinking Water Act standards.  However, small water systems and other private wells are not required to be tested.  The Corps is focusing on these small water systems and private wells located near contaminated groundwater.  For the past several years, all residential wells that were tested for TCE in Cascade Valley have met safe drinking water standards.

While annual testing of private wells has been ongoing for more than a decade, the Corps increased sampling to quarterly monitoring at properties where there is a risk of exceeding Safe Drinking Water Act standards.  If contaminants are detected above a certain threshold for drinking water, than the EPA will install a whole-house filtration system to remove TCE so concentrations do not exceed the Safe Drinking Water Act standards.