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Effects of Mining on Surface Water Changes in the quantity of water to the prevailing hydrologic balance are primarily due to the location and timing of flows. It is difficult to define any changes due to mining in the Grassy Creek basin because baseline data collected in 1980 include the influence of 12 years of previous mining activity at Seneca II Mine. The Fish Creek drainage, however, does indicate a change in the ground and surface water systems. Mining has increased the amount of ground water available to be discharged into the surface water system, due to discharging spoil aquifers. Cow Camp Creek now exhibits perennial stream flow as a result of mining in this drainage whereas prior to mining the creek emphemeral stream flow conditions existed. Data are insufficient to demonstrate whether short term decreases in stream flow are due to initial filling of ponds and resaturation of backfilled spoils. However, it is apparent that any depletion is extremely short-lived. Variability in annual amounts of precipitation supplied to the watershed makes it difficult to assess short term changes; however, long-term changes in flow are expected to be minimal. Three primary impacts on surface water quality were identified: 1) increased erosion and sediment yield; 2) exceedences of applicable water quality standards; and, 3) increased total dissolved solids loading. Increased Erosion and Sediment Yield During the active mining phase, and until sufficient vegetation can be established in the watershed, sediment yields above pre-mining levels are expected. Annual sediment surveys of the sediment ponds at the Seneca II Mine were initiated in 1985. These surveys will allow actual amounts of sediment deposited to be quantified. With continued monitoring, comparisons to estimated design volumes and erosion rates can be made. Throughout mining, the ponds have ensured compliance with effluent limitations prior to discharge from the mine site, and at no time during the last five years have limitations for total suspended solids been exceeded.. Water Quality Standards A comparison of Grassy Creek water quality at SW-S2-1, upstream of mining activities, to that of SW-S2-2, downstream of mining shows a slight degradation of water quality. SW-S2-2 shows a slight increase in metals concentration, sulfate, and total dissolved solids. These increases can be attributed to mining in the drainage and to the installation of a truck washing facility of NPDES outfall 003, immediately upstream of SW-S2-2. There are no receiving stream standards designated for Grassy Creek but water quality in Grassy Creek generally meets the standards established for Fish Creek. Water quality in Fish Creek shows no significant impact associated with mining. Data collected at site SW-S2-13, downstream from mining activities meets receiving stream standards. Pond outfalls (NPDES outfalls 002, 003, 004, and 005) are monitored according to the requirements of the Seneca II Mine NPDES permit (see section B of this document "Monitoring"). With the exception of the Northwest Impoundment and Pond 004, no parameters have exceeded limitations in the past five years. -2 3-