Southern Willamette Valley Groundwater Management Area

A Groundwater Management Area (GWMA) is a tool used by the Oregon Department of Environmental Quality to address a large scale groundwater contamination when the contaminants originate from non-point sources. The action level for an Oregon GWMA to be declared is 7 mg/L, or 70% of the public drinking water standard of 10 mg/L. There are three GWMA’s in Oregon, two on the eastern side of the state in the Lower Umatilla Basin and in Northern Malheur County were established in 1990 and 1989, respectively with the southern Willamette Valley GWMA being established in 2004. The southern Willamette Valley (SWV) GWMA was established after testing 476 shallow wells (< 75 feet) testing in 2000 – 2001; 20% of those wells had nitrate-N values over 7 mg/L. In 2002 all of the high wells were retested, over 90 % of them were still above the action level. The SWV GWMA committee was established, consisting of two county commissioners, realtors, three local commercial farmers, a fertilizer representative, public water supply operator and a watershed council representative. About 90% of the land use in the SWV is agriculture. To monitor the long term progress of the groundwater quality, 17 domestic and 26 groundwater monitoring wells are quarterly sampled by ODEQ. Quarterly measurements include pH, temperature, dissolved oxygen, nitrate-N, specific conductance, chloride and sulfate is measured bi-annually. The Environmental Protection Agency has performed stable isotope analysis to delineate the source of water from each well.