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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 are expected. Annual <br />sediment surveys of the sediment ponds at the Seneca II 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 discharge from the mine site, and at no time during the <br />last five years 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 outfall 003, immediately <br />upstream of SW-S2-2. There are no receiving stream standazds designated for <br />Grassy Creek but water quality in Grassy Creek generally meets the standards <br />established for Fish Creek. <br />Water quality in Fish Creek shows no significant impact associated with mining. <br />Data collected at site SW-S2-13, downstream from mining activities meets receiving <br />stream standards. <br />Pond outfalls (NPDES outfalls 002, 003, 004, and 005) aze monitored according to <br />the requirements of the Seneca II Mine NPDES permit (see section B of this <br />document "Monitoring"). With the exception of the exceedence of oil and grease in <br />1992 and total suspended solids (TSS) in 1995 at the Northwest Impoundment (003), <br />no parameters have exceeded limitations in the past five years. <br />The Northwest Impoundment (003) discharged oil and grease at 12 mg/I on March <br />11, 1992. A total petroleum hydrocarbon (TPH) analysis was performed on the <br />same sample with a value of <0.2 mg/I. Subsequent oil/grease samples collected in <br />April and May were below the detection limit. On March 21, 1995, a TSS value of <br />52 mg/1 was observed. The exceedence was a precipitation related event. On that <br />same date, Grassy Creek below NPDES 003 site had a TSS of only 10 mg/l. <br />Increased Total Dissolved Solids Loading <br />An increase in salinity, as represented by TDS concentrations, is the major surface <br />zs <br />