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• {h dttduw: Uw/ l,~rrrprrr/riun wrd lnipucr aeer_.,ninu fur drr Ycnnir /rrd: ldl/rnu aruc . withdrawal was L?0,779 gpd fur_llll working Vacs. .I ~ estimated to hace been 74 acre lest. This decrease in usage can he attributed «~ c~m- pletion of surface construction projects (water was The quality- u( mine water is considered gaud and used for dust control, compaction, concrete pro- offers no problem for treatment and discharge. duction, etc.). Mine water was primarily discharged from the Water from the freshwater pond(s) is used in two ways. It can be treated to meet potable and sani- tary water requirements, used, and then treated as sanitary waste water. Or, it can ha withdrawn for dust suppression in the mine. in which case it then becomes mine water. MCC's Mt. Gunnison pipeline water rights were out of priority during a portion of water vear 1991 between Julv 23, 1992 and October 1. 1992. Aver- age daily low tluw in the North Furk during water year 1992 was 347 cfs. The maximum withdrawal at the intake is 450 gpm with both pumps operating. This is about 0.3 percent of thz ohsened a+crage daily low flow in the river durine the water }car. Sanitary Waste Water The sanitary waste water treatment plant has been • operating since the fall of 193?. During water year 1992, discharge from the plant a+eraged 0.0043 cfs. This discharge is approximately 0.0012 percent of the average daily flow of 347 cfs observed in the North Fork during the year. Discharge monitoring results from the waste water treatment plant, conducted under NPDES Permit Nu. CO-0033776, are included in Appendix J. There were two isolated incidents of effluents exceeding permit limitations. During monitoring period 1 October - 31 December 1991, actual residual chlorine reached Q6~ vs. permit limitation of 0.5; and during 1 July - 30 Szptember 1992 actual total suspended solids was 76.4 cs. a permit limitation of 45. Both incidents appear to be exceptions as the parameters were within limits at all other times. Thc results of the analyses suggest the waste water discharge has nu measurable effect on water quality in the North Fork Gunnison River. Mine Water Mine inflows during water year 1992 were small. The total mine water inflow was 63? acre (ect during the year. The total water exiting the mine is Nu. 2 Portal. Nu discharces occurred from Sylves- ter Gulch or Portal No. 5. Mine water inflow for water year 1993 is cxpceted to be Icss than that experienced during water ccar 1992. Onl_v the amount of water necessary (or mining will be imported into the mine. Mine water is expected to have water quality characteristics similar to that reported in Table ?. Because of the small quantity of mine water anticipated, any discharge from ponds would normally he dominated by water quality character- istics u( 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 u( six sediment ponds on the mine site. The six sediment ponds are designed to contain the predicted runoff from a statistically determined l0 year, 24 hour precipitation event as well as a calculated sediment storage volume. The ponds arc also designed to pass the overflow from a 3~ year. 24 hour prccipi- tatiun event safely. The West Elk Mine site receives much ul us annual precipitation from snowfall during the winter months. When warmer weather begins in late February, March or April, most runoff to the sediment ponds is from snowmelt. It is emirely possible (or a volume of runoff greater than the l0 year, 24-hour precipitation event to result from snowmelt or snowmelt coupled with a small precip- itation event. The sediment ponds are treated with cationic flocculent when necessary w speed clarification and settling of suspended solids. The ponds MB-1, MB-2, MB-5, and MB~i have manually controlled dewatering devices. Ponds MB-3 and MB-4 have automatic dewatering capabilih-. Ponds MB-l. MB-'_, MB-= and MB~i are dewatered intermit- tently with most discharges coming during early spring runoff. Dewatcring procedures take usually l2