The U.S. Geological Survey, in cooperation with the Tennessee Department of Health and Environment, Division of Groundwater Protection, and the Jackson Utility Division, conducted a pilot study to determine data needs and the applicability of four methods for the delineation of wellhead protection areas. Jackson Utility Division in Jackson, Madison County, Tennessee, pumps about 9 million gallons of ground water daily from two municipal wellfields that tap an unconfined sand aquifer. Under natural hydraulic gradients, ground waterflows southward toward the South Wellfield at approximately 2 to 3 feet per day; natural flow toward the North Wellfield from the east at 1 to 2 feet per day. Water quality generally is suitable for most uses. Concentrations of dissolved solids are low, and excessive iron is the only significant naturally occurring water-quality problem. However, trace concentrations of volatile organic compounds have been detected in water pumps from the South Wellfield; the highest concentration of a single compound has been 23 micrograms per liter of tetrachloroethylene. Potential sources of ground-water contamination in the Jackson area include a hazardous-waste site, municipal and industrial landfill, and underground-storage tanks. Some of the four method for delineating wellhead protection areas did not adequately describe zones contributing flow to the wellfields. Calculations based on a uniform flow equation provided a preliminary delineation of zones of contribution for the wellfields and ground-water time-of-travel contours. Limitations of the applied methods motivated the design of a more rigorous hydrogeologic investigation.
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A pilot study for delineation of areas contributing water to wellfields at Jackson, Tennessee