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~J <br />n <br />U <br />the river were taken 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 often times less <br />than the differences expected from measurement errors. Recent annual <br />hydrologic reports estimate an average annual River load of 1.0 to 1.5 million <br />tons of salt. The projected additional load from the mine discharge is about <br />1,000 tons, which amounts to about an 0.001 % increase. <br />Sediment concentrations from the mine discharge has consistently been within <br />effluent limitations. Therefore, the impact to the river form sediment is negligible. <br />Effects of Surface 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. Usually, <br />the treatment of choice is a sediment pond, and the sediment ponds are used at <br />all of the major portals and at the refuse piles. At times, alternative sediment <br />control measures are used to treat runoff from small areas where sediment <br />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 Creek, Cottonwood Creek, and Cabin <br />Reservoir. These pillars are designed to prevent subsidence, and therefore, <br />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 />Monitoring at this station was subsequently suspended. <br />Therefore, plans are in place to protect the creeks from subsidence and <br />monitoring is in place to evaluate the effectiveness of the protection plans. <br />• 19-9 (5/03) <br />