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Effects of Minine on Surface Water <br />Changes in the quantity of water to the prevailing hydrologic balance aze primarily <br />due to the location and timing of flows. It is difficult to define any changes due to <br />mining in the Grassy Creek basin because baseline data collected in 1980 include the <br />influence of 12 years of previous mining activity at Seneca II Mine. The Fish Creek <br />drainage, however, does indicate a change in the ground and surface water systems. <br />Mining has increased the amount of ground water available to be discharged into the <br />surface water system, due to discharging spoil aquifers. Cow Camp Creek now <br />exhibits perennial stream flow as a result of mining in this drainage whereas prior to <br />mining the creek ephemeral stream flow conditions existed. <br />Data are insufficient to demonstrate whether short term decreases in stream flow are <br />due to initial filling of ponds and resaturation of backfilled spoils. However, it is <br />apparent that any depletion is extremely short-lived. Vaziability in annual amounts <br />of precipitation supplied to the watershed makes it difficult to assess short term <br />changes; however, long-term changes in flow aze expected to be minimal. <br />Three primary impacts on surface water quality were identified: 1) increased erosion <br />and sediment yield; 2) exceedences of applicable water quality standazds; and, 3) <br />increased total dissolved solids loading. <br />Increased Erosion and Sediment Yield <br />During the active mining phase, and until sufficient vegetation can be established in <br />the watershed, sediment yields above pre-mining levels aze expected. Annual <br />sediment surveys of the sediment ponds at the Seneca lI Mine were initiated in 1985. <br />These surveys will allow actual amounts of sediment deposited to be quantified. <br />With continued monitoring, comparisons to estimated design volumes and erosion <br />rates can be made. Throughout mining, the ponds have ensured compliance with <br />effluent limitations prior to dischazge from the mine site, and at no time during the <br />last five yeazs have limitations for total suspended solids been exceeded. <br />Water Ouality Standazds <br />A comparison of Grassy Creek water quality at SW-S2-1, upstream of mining <br />activities, to that of SW-S2-2, downstream of mining shows a slight degradation of <br />water quality. SW-S2-2 shows a slight increase in metals concentration, sulfate, and. <br />total dissolved solids. These increases can be attributed to mining in the drainage <br />and to the installation of a truck washing facility of NPDES outfa11003, immediately <br />upstream of SW-S2-2. There aze no receiving stream standazds designated for <br />24 <br />