An Approach to Understand Water Quality Trends in Groundwater in the Columbia Plateau, Washington, Oregon and Idahi

Groundwater of the Columbia Plateau basaltic aquifer in Washington, Oregon, and Idaho was sampled as part of an assessment of water-quality in principal aquifers of the United States conducted the U.S. Geological Survey National Water-Quality Assessment Project. The Columbia Plateau principal aquifer consists of the basaltic rocks of the Columbia River Basalt Group. Water from approximately 60 wells in Oregon, Washington, and Idaho was collected and analyzed using nationally consistent protocols for a suite of constituents including major ion chemistry, nutrients, radiochemistry, volatile organic compounds, pesticides, pharmaceuticals, trace elements, stable isotopes of water, and age-tracers. The groundwater quality information will be used to understand water quality for comparison with past and future conditions, evaluate horizontal and vertical variation in water quality, and assess the source, age, and sustainability of groundwater supplies.