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u • 2.0 Nydrologir Dara lnrcrprelarion and /rnpart Assestmenr for the Permit and Adjarrnt Arear 2.5 MINE WATER MANAGEMENT AND IMPACT ASSESSMENT The discussion of the mine water system and hydrologic impact assessment is organized by the four sources of water: • North Fork water • sanitary wastewater • mine water, and • runoff from disturbed areas. Use and discharge of water from these sources is studied for its potential to affect the North Fork. 2.5.1 North Fork Water The annual 1994 WY mean flow on the North Fork of the Gunnison was 382 cfs, lower than the mean flow for the 1993 to present historic recording period, of 456 cfs. The annua) seven-day minimum occurred January 26 to February 1 and averaged 50 cfs. The maximum flow occurred May 13 and was 2,580 cfs. MCC water rights were out of priority from July 12, 1994 through September 2, 1994. The maximum withdrawal at the intake North Fork of the Gunnison galley is 450 gpm with both pumps operating. This is probably less than 0.5 percent of the average daily low flow in the river during the water year. During 1994, the average withdrawal was 257,291 gpd for 250 working days. This increase in usage (from 159,276 gpd in WY 1993) can be attributed to more consistent operation of the longwall and the resultant increase in production. R1.210/IOA/OS/OS/95(8.04am} 24 2.5.2 Sanitary Waste Water Sanitary waste water discharges from the Waste Water Treatment Plant (WV/TP) are monitored at discharge point 007. Dis- charge flows to MB-2R where additional detention occurs. During May of 1994, discharges exceeded permit conditions for TSS, BOD and removal rates of the same. MCC repaired the aeration blowers' cycling mechanism and compliant discharges resulted. The analyses suggest the waste water discharge has no measurable effect on water quality in the North Fork Gunnison River. 2.5.3 Mine Water The total WY 1994 mine water inflow from natural mine inflow and water pumped underground was 174.9 acre feet during the year (Table 1.6-1). The total water pumped from the mine and discharged to surface waters was approximately 79 acre feet. The quality of mine water is considered good. Mine water was primarily discharged from the No. 2 Portal. No discharges oc- curred from Sylvester Gulch or Portal No. 5. Because of the small quantity of mine water anticipated, any discharge from ponds would normally be dominated by water quality characteristics of disturbed area runoff as described in the following section. 2.5.4 Runoff from Disturbed Area Mine site runoff is treated by ponds MB-1, MB-2R, MB-3, MB-4 and MB-5. All water discharged from the ponds MB-1 and MB- 2R was in compliance with NPDES permit effluent limitations (Table J-1). During