Assessment of water quality impacts of a western coal mine. [10 refs]

This report describes interim results of a water quality investigation carried out during 1975 and 1976 in the vicinity of the Big Horn Mine, an operating surface coal mine in the northwestern part of the Powder River Basin, Wyoming. The mine has been operated for approximately 20 years and is one of the several operating or proposed mines in the basin. Present coal production is about 1,000,000 tons (approximately 910,000 MT) per year. The effect of the Big Horn Mine on concentrations of dissolved conservative constituents in the Tongue River is small, and is within the range of analytical precision and short-term variations in ambient concentrations. On the other hand, there are large changes in stream water quality evident in upstream reaches of the Goose Creek and Tongue River watersheds, where intensive agricultural activity exists. Trace element concentrations are relatively low at all stream and mine discharge sampling points, and it does not presently appear that toxic trace elements will present environmental problems at this site (Olsen and Dettmann, 1976). Ammonium and nitrate concentrations are elevated in the Big Horn Mine discharges (possibly due to use of ammonium nitrate explosives) relative to levels in the streams, but phosphorous concentrations aremore » not. Material balance calculations indicate that present loading by pumped mine discharges from the Big Horn Mine could locally increase ammonium and nitrate concentrations in the Tongue River by approximately 3 and 1 percent, respectively.« less