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• Hydrologic Qam /nrerprem6on and Impact A.sseumnu Jor Pettit Arca 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 September, but 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 and an additional portion was deemed absolute by the Division 4 water court bringing the absolute portion to 0.88 cfs. Sanitary Waste Water The sanitary waste water treatment plant was constructed and completed in the fall of 1982. During water year 1988, discharge from the waste water treatment plant averaged 3600 gpd. This discharge is approximately 0.01% of the average daily low flaw of 49 cfs observed in the North Fork during the year. Discharge monitoring results From the waste water treatment plant, conducted under NPDES Permit No. CO-0038776, are included in Appen- dix I. 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 The 10-acre-foot capacity pond provides for water storage during the term of permit; two ponds are 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 1988 average withdrawal was 7,200 gpd for 250 working days. Water from the freshwater pond(s) is either treated to meet potable and sanitary water re- quirements, used, and then treated as sanitary waste water, or it is withdrawn for dust suppres- sion in the mine, in which case it then becomes mine water. WECC's Mt. Gunnison pipeline water rights were out of priority during a large portion of water year 1988 (from approximately 15 June through 30 September). Average daily low [low in the North Fork during water year 1988 was 49 cfs during one day in December 1987. The maximum withdrawal at the intake is 450 gpm with both pumps operating. This is less than 2.04 percent of the observed average daily low flow in the river during the water year. Mine inflows during water year 1988 were small. The total mine water inflow was 21.0 acre feet during the year. The total water exiting the mine is estimated to have been 16.78 acre feet. The quality of mine water is considered good and offers no problem for treatment and dis- charge. Mine water was discharged only from the No. 2 Portal. No discharges occurred from Syl- vester Gulch. Table 4 shows the quality of water discharged at Portal No. 2. Mine water inflow [or water year 1989 is expected to be similar to that experienced during water year 1988. Mine water would be expected to have water quality characteristics similar to tha[ reported in Table 4. Because of the small quantity of mine water anticipated, any discharge from ponds would normally be dominated by water quality charac- teristics of disturbed area runoff as described in the following section. Runoff from Disturbed Area Overland runoff from snowmelt and precipita- tion within the disturbed areas is routed to one of six sediment ponds on the mine site. The six sediment ponds are designed to contain the predicted runoff from a statistically determined 10 14