Groundwater Under the Pacific Northwest • November 2-3, 2005 • Stevenson, Washington

ABSTRACT

Perchlorate Occurrence in the Lower Umatilla Basin, Oregon

Presenter: Phil Richerson, Oregon Department of Environmental Quality
Co-Authors: David Anderson, John Dadoly, Harry Craig, Ken Marcy

Oregon Department of Environmental Quality (ODEQ) and the United States Environmental Protection Agency (USEPA) are conducting a large-scale investigation into the occurrence and sources of perchlorate (ClO₄^-) in northeastern Oregon. The area is currently under investigation for the occurrence and distribution of nitrate as part of ODEQ’s Lower Umatilla Basin Groundwater Management Area. The current perchlorate investigation is coincident with this area.

Perchlorates are used extensively in industry in the production of military explosives, rocket and missile fuels, fireworks, flares, matches, dyes, lubricants, paints, rubber products and pharmaceuticals. Perchlorates have also been found in some naturally-mined nitrate and phosphate fertilizers, particularly rock fertilizers from Chile.

Beginning in 1990, ODEQ began sampling wells in the area due to elevated nitrate contamination in the water. ODEQ regularly samples a network of wells to monitor nitrate concentrations. In early 2003, following review of groundwater data from several sites, a decision was made to submit some groundwater samples for explosives and perchlorate analysis. Subsequent analysis of groundwater samples from over 150 wells located across the area indicated widespread perchlorate detections. Perchlorate concentrations range from non-detect, to very low levels (<1 micrograms per liter [µg/L]) to higher levels (30 µg/L) commonly associated with possible source areas.

To date, perchlorate has been detected in groundwater and surface water in the area, with irrigation wells, community wells, and domestic wells being impacted. Although no current maximum contaminant level exists for perchlorate, risk-based concentration levels of 4 µg/L for sensitive populations to 25 µg/L for adults have been calculated that are based on the recently-released National Academy of Sciences reference dose of 0.0007 milligram per kilogram-day (mg/kg-day).

Currently, at least 25 domestic wells, several community wells, 46 monitoring and irrigation wells, and several surface water bodies have detectable concentrations of perchlorate over a concentration of 4 µg/L. The ODEQ and EPA have ranked this area a high priority for further evaluation and will be conducting ongoing investigation and analysis of source areas and determining the need for additional sampling.