Hydrogeologic information for western Oregon was compiled to aid the U.S. Environmental Protection Agency in evaluating proposals for underground injection of waste fluid. Geologic formations were grouped into seven aquifer units according to hydraulic and geologic similarities. The bedrock aquifer units in the Klamath Mountains, Coast Range, and Western Cascade Range all have low permeabilities and yield only small quantities of water to wells for domestic and stock uses. The Columbia River Basalt Group aquifer unit, which crops out along the Columbia River and the northern Willamette Valley, also has overall low permeability; however, the basalt supplies water for public, domestic, and stock, and some irrigation uses in western Oregon. The most important aquifer unit, and generally most permeable is the Tertiary-Quaternary sedimentary deposits that occur in lowlands throughout the area and provide water for irrigation, industry, public supplies and domestic and stock uses. All aquifer units generally contain water with low concentrations of dissolved solids at shallow depths. In the Tertiary marine rocks of the Coast Range, analyses from a limited number of deep wells indicated that water with more than 10,000 milligrams per liter dissolved solids is widespread at depths greater than about 2 ,000 feet. (USGS)
