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of the river was done between 1979 and 1987 for total dissolved solids, and the <br />results are summarized in the annual hydrologic reports. The difference <br />between upstream and downstream sample concentrations were frequently less <br />than the differences expected from measurement errors. Recent annual <br />hydrologic reports estimate an average annual river load of 1.52 million tons of <br />salt. The projected additional load from the four discharges is 1386 tons, which <br />amounts to a 0.091 % increase. <br />Sediment concentrations from the mine discharges have consistently been <br />within effluent limitations (Colorado Department of Health, 1992). Therefore, <br />the impact to the river from sediment is negligible. <br />Effects of Surtace Disturbances on Water Quality <br />Surface runoff from disturbed sites is treated before water leaves the permit <br />area, and sediment is controlled as close to the source as possible. Therefore, <br />• there is no increase in sediment yield as a result of mining operations. In most <br />cases sediment ponds are used to control runoff from the major portals and <br />refuse piles. Alternative sediment control measures are used when <br />needed to treat runoff from small areas where sediment ponds are not practical. <br />Summary <br />The probable hydrologic effects of underground mining are associated with <br />subsidence damage. Powderhorn Coal company has developed a mine plan to <br />leave protective pillars under Rapid, Cottonwood, Jerry and Coal Creeks, and <br />Cabin Reservoir. These pillars are designed to prevent subsidence, and <br />therefore,minimize impacts to the hydrologic balance. <br />Monitoring of the stream flow along Rapid Creek and Cottonwood Creeks has <br />not shown any loss of water due to subsidence. In 1993, monitoring was <br />expanded to include future mining areas with the addition of station SWGS-05. <br />• 19-9 (New 3/1/96) <br />