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Radon-222 activity was measured for 27 water samples from streams and ground water in and near the Owl Creek Basin, a 510-square mile area in north-central Wyoming. Water samples were collected from September 1991 through March 1992. Summary statistics of the radon-222 activities were compiled. The radon-222 activities were measured as part of a comprehensive study of surface-and groundwater quality in the Owl Creek Basin undertaken cooperatively by the U.S. Geological Survey and the Shoshone Tribe and Northern Arapahoe Tribe. Stream-water samples were collected at 16 sites along the main stem of Owl Creek and its tributaries. For the 16 stream-water samples, the arithmetic mean radon-222 activity was 20 pCi/L (picocuries per liter), geometric mean activity was 7 pCi/L, harmonic mean activity was 2 pCi/L, and median activity was 8 pCi/L. The standard deviation of the arithmetic mean was 29 pCi/L. The stream-water samples ranged from 0.4 to 97 pCi/ L. The histogram of stream samples are left-skewed compared to a normal distribution. Groundwater samples were collected at 11 sites from an alluvial aquifer, bedrock aquifers, and a geothermal system. For the 11 groundwater samples, the arithmetic mean radon-222 activity was 486 pCi/L, geometric mean activity was 280 pCi/L, harmonic mean activity was 130 pCi/L, and median activity was 373 pCi/L. The standard deviation of the arithmetic mean was 500 pCi/L. The radon-222 activities in the groundwater samples ranged from 25 to 1,704 pCi/ L. The histogram of groundwater samples are left-skewed compared to a normal distribution.

Water quality of the backfill aquifer associated with coal strip mining is a developing area of analysis where data are allowing regulators to move from depending on predictive techniques to reliance on data collected from the backfill aquifer. The chemical concentrations of dissolved arsenic, boron, cadmium, mercury, selenium, and aluminum in the backfill aquifer were examined. The data are from 84 wells located at 11 mines in the eastern Powder River Basin. A total of approximately 2,500 samples have been collected from 1977 to 2005 from monitoring wells in the backfill aquifer. Each chemical constituent is statistically summarized and compared to appropriate water quality standards. Changes in concentration of selected constituents from individual wells with longer periods of record are examined over time.Analysis indicates that mobilization of dissolved arsenic, cadmium, mercury, selenium and aluminum was not commonly encountered. Nondetection was common in the data set with dissolved arsenic not detected in 90 percent of the samples, dissolved cadmium at 95 percent, dissolved mercury at 98 percent, dissolved selenium at 81 percent and dissolved aluminum at 84 percent. Dissolved boron was detected in 84 percent of the samples, but generally at low concentrations. Dissolved boron had a median concentration of 0.1 mg/L.

Abstract:In the Powder River Basin of Wyoming, water quality monitoring data were evaluated for a number of wells completed in mine backfill, which have sufficiently recharged for evaluation of mining impacts on water quality. Based on the data reviewed to date, the backfill water quality is usually similar to baseline water quality in the Wyodak-Anderson coal aquifer and Wasatch overburden. However, as the backfill materials recharge, the trends in the concentrations of specific constituents (in particular, total dissolved solids and sulfate) may reflect sitespecific conditions, including: proximity to recharge sources (e.g., clinker, unmined coal, and coal fenders between mines); changes in mining activities (e.g., temporary cessation of mining); and local conditions (e.g., leakage from impoundments). In some situations, constituent concentrations increase over time, while in others, constituent concentrations are relatively constant or are decreasing.