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West 6!k Mine The increases in TDS would appear to pose concern upon initial inspection, for example, the • October TDS increase was from 90 mg/L upstream from the mine to 244 mg/L downstream from the mine; however, WWE has thoroughly evaluated the implications of this and other TDS increases, and the analysis demonstrates that the increases did not cause exceedances of relevant criteria/standards, nor did they result in any adverse impacts to downstream beneficial uses. In addition, the CWQCD approved direct discharge of high TDS water from the B East Mains fault inflow to the North Fork via the emergency spillway of pond MB-1. Of potential concern is the high sodium level in releases from the sedimentation ponds; yet conservative calculations show that downstream irrigated agricultural lands would not have been adversely affected by the increased sodium levels. Discharge of Sanitary Wastewater The NPDES Permit allows for aflow-through rate of 20,000 gpd, based on a 30 day average, from the sanitary wastewater treatment plant (WWTP). The potential impacts of effluent can be conservatively estimated using the NPDES discharge limits. Discharges from 1983 to 1988 are included in Table 59. This table also compares the discharges to the flow of the North Fork, and shows that discharges are very small relative to even low flows in the river. The potential impact of discharge of wastewater effluent would be greatest when the dilution ratio for effluent is smallest. Table 60 contains data which show the effect of wastewater discharges on the North Fork from 1983 to 1988. The discharges are small compared to the • total river flow, even when compared to the infrequent low flows which represent the worst case condition for discharges. Background concentrations were conservatively estimated. Nitrate and TSS backgrounds were determined from the maximum concentrations measured during low flows (under 300 cfs). Background for ammonia nitrogen and fecal coliform were determined from maximum observed concentrations. Table 59 and 60 indicate that impacts of wastewater discharges from West Elk Mine to the North Fork have been insignificant. Table 59 Effects of Wastewater Treatment Plant Discharge on the North Fork Year Discharge(MGD) Average Max. Daily Low Flow North Fork (MGD) Discharge From WWTP (acre feet) Annual Yield of North Fork (acre feet) 1983 0.0017 0.0035 23.27 1.93 284,913 1984 0.0056 0.0090 18.10 6.21 303,414 1985 0.0052 0.0075 36.84 5.72 289,996 1986 0.0048 0.0102 51.71 5.38 291,290 1987 0.0033 0.0051 31.67 3.70 192,500 1988 0.0036 0.0071 34.98 4.03 113,200 • 2.05-207 Revised Jun. 1995 PR06; Revised Nov. 1998 TR80. Rev~sedJan. 1998 PR08