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West 61k Mine <br />Runoff from mine site areas is collected and treated in sediment ponds, except for a few areas <br />designated as Small Area Exemptions (see Exhibit 66). Data from these discharges is included <br />in the MCC Quarterly Hydrology Reports (1982 to 1987) and in the Annual Hydrology <br />Reports (1982 to present). Dischazges have complied with NPDES/CDPS permit requirements <br />with only a few minor exceptions. No significant impacts to the North Fork from sediment <br />pond discharges have been observed or are indicated by sample results. <br />s <br /> <br />Table 50 summarizes quarterly NPDES water quality from sediment pond MB-2R from <br />October 1993 through September 1994, and aze indicative of the mine site pond water. It is <br />apparent from the previous quarterly monitoring reports and Table 50 that sediment pond <br />dischazges have no adverse effect on the North Fork or water quality standazds. The quality of <br />pond discharge often exceeds the quality of the North Fork and so provides dilution. The <br />discharge flows are small relative to the North Fork flow, so that incremental changes in <br />concentrations are imperceptible. <br />All discharges aze treated to meet effluent limits. Comparison of Table 50 values to effluent <br />limits in Table 51 shows that the pond discharges typically meet the effluent limits for the <br />pond. Sedimentation in the ponds reduces levels of total suspended solids (TSS), and the pH <br />typically decreases as pond water equilibrates with the atmosphere. Total iron, pH, and TDS <br />in discharges resulting from future mining should be similar to the values reported in Table 50. <br />Table 50 Summary of Discharge Water Quality From Sediment Pond MB-2R <br />Parameter No. of Samples Mean Minimum Maximum <br />pH (S.U.) 19 8.1 7.4 8.6 <br />TDS (mg/L) 19 596 349 1190 <br />TSS (mg/L) 19 12.6 0.9 47 <br />Total Iron (mg/L) 19 0.26 L.D. 1.22 <br />Table 51 NPDES Effluent Limits for Discharge From Sedimentation Ponds at <br />the West Elk Mine <br />Effluent Characteristics Maximum Allowable (mg/L) 30-Day Average (mg/L) <br />Total Suspended Solids 70 35 <br />Total Iron 7.0 3.5 <br />Oil and Grease 10.0 - <br />pH (S.LT.) 6.5 to 9.0 -- <br />2.5-189 ReviudJun. /995 PR06; RevaedNw. 1998 TR80: !/98 PR08 <br />