Surface- and ground-water quality in the Owl Creek basin, north-central Wyoming
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Water quality of surface water and ground water in the Owl Creek basin is characterized and compared to the U.S. Environmental Protection Agency (EPA) maximum contaminant levels (MCL) or secondary maximum contaminant levels (SMCL) for concentrations of sulfate, chloride, fluoride, dissolved solids, and nitrate. Water samples from two sources--streams in the upper basin segment of Owl Creek basin and springs issuing from a bedrock aquifer in the Absaroka Volcanic Supergroup--have concentrations less than the associated MCL or SMCL. Surface-water quality in Owl Creek basin is separated into three basin segments. That separation is based on differences in the following: dissolved-solids concentrations, water type, and relation of dissolved-solids concentration to specific conductance. Only concentrations in water samples from streams in the upper basin segment are less than the MCL or SMCL. In the middle and lower basin segments, the averages of dissolved-solids concentrations of water samples exceed the SMCL. There is a distinct linear relation between dissolved-solids concentration and specific conductance in each basin segment. Concentrations of selected constituents in water samples from the Arapaho Ranch alluvial aquifer and selected bedrock aquifers also are compared to the associated MCL or SMCL. The average dissolved-solids concentration in water samples from the Arapaho Ranch alluvial aquifer exceeds the associated MCL by more than two times, primarily because of large concentrations of sodium, alkalinity, and sulfates. A strong linear relation exists between dissolvedsolids concentration and specific conductance in the Arapaho Ranch alluvial aquifer. Selected bedrock aquifers are evaluated. Only concentrations of dissolved constituents in samples from the Absaroka Volcanic Supergroup in Owl Creek basin are equal to or less than the associated MCL or SMCL. Limited water-quality analyses are available for the other potential aquifers: Cody Shale, Frontier Formation, Lower Cretaceous to Jurassic rocks, Tensle