MOSES LAKE WELLFIELD CONTAMINATION
(a/k/a SKYLINE WATER SYSTEM)
MOSES LAKE, GRANT COUNTY, WASHINGTON
The Washington State Department of Health (DOH) has prepared this health consultation under cooperative agreement with the Agency for Toxic Substances Disease Registry (ATSDR), an agency of the U.S. Public Health Service. The goal of the DOH and ATSDR is to identify and mitigate adverse human health effects resulting from exposure to hazardous substances in the environment. This report was prepared in accordance with methodologies and guidelines developed by ATSDR.
A health consultation provides advice on specific public health issues which may arise as a result of an actual or potential human exposure to a hazardous substance. Health consultations provide a means for DOH to respond quickly to a request for health information on hazardous substances and to make recommendations for actions to protect public health. DOH evaluates available information about hazardous substances at a site, determines whether exposures have occurred or could occur, and reports the potential harmful effects from exposure.
For additional information regarding this health consultation, contact:
Rob Duff, Public Health Assessor
Washington State Department of Health
Office of Toxic Substances
P.O. Box 47825
Olympia, WA. 98504-7825
This health consultation was written in response to a request made by the Washington State Department of Health (DOH) Division of Drinking Water to clarify the health risks associated with exposure to trichloroethylene (TCE) in the Skyline Water System (Skyline). The DOH Office of Toxic Substances prepares health consultations under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). This health consultation will examine new data relative to TCE in Skyline drinking water and discuss the current potential health risk associated with exposure to this water.
The Skyline Water System consists of two public wells located between Airway Drive and Route 17 approximately 2 miles south of the Grant County Airport and 2 miles northeast of the City of Moses Lake. These wells serve approximately 80 homes in the immediate vicinity. Well #1 provides continuous service throughout the year while Well #2 is used at times of high demand (e.g. summer months). TCE was first detected in February 1988 at a concentration of 7.5 ppb in Well #2. Sampling in December 1988 detected TCE in both Well #1 at 11.5 ppb and Well #2 at 6.5 ppb. The Washington State Department of Social and Health Services evaluated these levels of TCE in Skyline water in December 1988. This evaluation concluded that drinking water containing TCE above the Maximum Contaminant Level (MCL) of 5.0 parts per billion (pbb) should not be used for drinking or other household uses.  A Preliminary Public Health Assessment released by ATSDR in June 1993 concluded that a public health hazard existed for residents drinking Skyline water over a long period of time. 
The area surrounding and including the Skyline wells was listed by the U.S. Environmental Protection Agency (EPA) on the National Priorities List (Superfund) as the Moses Lake Wellfield Contamination site (WAD988466355) in October 1992. Much of this area includes the former Larson Air Force Base and Grant County Airport. The EPA is currently requiring that a Remedial Investigation/Feasibility Study (RI/FS) be performed in order to determine the source of the TCE groundwater contamination and the necessary measures to address it. Bottled drinking water has been made available to residents using Skyline water since March 1994.
Since the initial detections in 1988, TCE has been consistently found in each of the Skyline wells. The levels in Well #1 have declined to an average of approximately 5 ppb but have been as high as 6.7 ppb. TCE levels in Well #2 have increased reaching a maximum of 32.2 ppb. The most recent sampling of these wells found TCE in Well #1 at 4.4 ppb (September 1998) and Well #2 at 30 ppb (June 1997). On June 30, 1998, DOH instructed the owner of the Skyline Water System to use Well #2 only if Well #1 failed. Well #2 has not been in use since October, 1997.