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• • Hydrologic Data In+erprcta+ion and lmpac+ Assr_snnen+ for the Permit and Adjacrnt Arear North Fork Water During water year 1982, the conditional right to withdraw water from the North Fork was deemed absolute. When this water right is in priority, water can be pumped from the intake point to the freshwater storage pond(s) within the surface facilities area. In average years, this water right is expected to be out of priority from July to Septem- ber. In 1977, it would have been out of priority from April to September. in water year 1986, WECC's Mt. Gunnison Pipeline water right met quadrennial diligence for the conditional portion. Accordingly, an additional portion was deemed absolute by the Division 4 Water Court. That decision brought the absolute portion to 0.88 cfs. The ]0-acre-foot capacity pond (FW-1) provides for water storage during the current permit term; an additional pond (SW-2) is anticipated for subsequent permit terms. Water can also be stored in Sediment Ponds MB-1, MB-2, and MB-3 under a separate decree. Storage is usually limited to the maximum sediment level elevation. Transfer to FW-1 is possible as outlined in the M & R Plan. Average withdrawals are not expected to exceed 50,000 gpd during the term of permit and are likely to be on the order of 45,000 gpd, depending on production levels and requirements. During 1990 average withdrawal was 97,000 gpd for 250 working days. This two-fold increase in usage can be attrib- uted to the drilling and blasting work completed in the "B" seam slopes and ventilation raise. Water from the freshwater pond(s) is used in two ways. It can be treated to meet potable and sani- tarywater requirements, used, and then treated as sanitary waste water. Or, it can be withdrawn (or dust suppression in the mine, in which case it then becomes mint water. WECC's Mt. Gunnison pipeline water rights were out of priority during a portion of water year 1990 (from approximately July to September). Average daily low flow in the North Fork during water year 1990 was 210 cfs. The maximum withdrawal at the intake is 450 gpm with both pumps operating. This is less than 0.5 percent of the observed average daily tow Oow in the river during the water year. Sanitary Waste Water The sanitary waste water treatment plant has been operating since the fall of 1982. During water year 1990, discharge From the plant averaged 3700 gpd. This discharge is approximately 0.0027 percent of the average daily low (low of 210 cfs observed in [he North Fork during the year. Discharge monitoring results from the wastewater treatment plant, wnducted under NPDES Permit No. CO-0038776, are included in Appendix J. The results of the analyses suggest the waste water discharge has no measurable effect on water quality in the North Fork Gunnison River. Mine Water Mine inflows during water year 1990 were small. The total mine water inflow was 61.50 acre feet during the year. The total water exiting the mine is estimated to have been 58.25 acre feet. The quality of mine water is considered good and offers no problem for Ircatmcnt and discharge. Mine water was primarily discharged from the No. 2 Portal. No discharges occurred from Sylves- ter Gulch. Mine water inflow for water year 1991 is expected to be less than that experienced during water year 1990. After construction of "B" seam slopes and raise and rehabilitation of "F' seam entries are complete, only the amount of water necessary for mining will be imported into the mine. Mine water is expected to have water quality characteristics similar to that reported in Table 5. Because of the small yuamity of mine water anticipated, any discharge from ponds would normally be dominated by water quality charactcr- istics of disturbed area runoff as described in the following section. Runoff from Disturbed Area Overland runoff from snowmelt and precipitation within the disturbed areas is routed to one of six sediment ponds on the mine site. The six sediment 14