USGS Washington Water Science Center
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WA331 - Ground-Water Quality of Clark County - Completed FY1989
Problem - Clark County, in southwestern Washington, is almost entirely dependent on ground-water resources for water supply and has petitioned the State of Washingt for designation of Clark County as a ground-Water Management Area. Such designation will enable the county to receive state funds for development of a ground-water management plan, which includes a study of the physical and chemical characteristics of the ground water. To assist the county in developing the plan, the Oregon State Office of the U.S. Geological Survey (USGS), Water Resources Division (WRD) has initiated a cooperative study to identify hydrogeologic characteristics of the ground-water system which will ultimately result in a ground-water flow model to be used as a management tool. That study does not, however, address the need to characterize the quality of the ground water.
Objectives - The Washington State Office of the USGS will determine concentrations of inorganic and organic constituents in the ground water on a county-wide scale. Variations in constituents as a function of area, depth, and aquifer will be defined. The USGS will also attempt to use constituent concentrations to refine generalized ground-water flow paths as determined from water levels and to identify sources of constituents in ground water.
Approach - Existing well logs and water-quality data contained in USGS, Environmental Protection Agency (EPA), Washington State Department of Ecology (SDOE), and Clark County files will be reviewed to select wells suitable for water-quality sampling. Samples will be collected from about 75 wells throughout the county. All samples will be analyzed for concentrations of major ions and other inorganic constituents and properties needed to characterize ground-water chemistry, plus selected bacteria and radon; samples from 20 wells will also be analyzed for pesticides, volatile organic compounds, and dissolved metals. Resulting data will be tabulated and used in preparation of a statistical summary report. The report will also discuss relations between water chemistry and ground-water flow.