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• Hrdrtdu+ir Uw ~ hur'I(Vt (J(IO/I JRIIVIIrI(rtlQ :I1dC1d111(II( fur thr Ymrnt mid :4!(airr¢ Ar=ax, _ <br />/ V ~ ..~ `^nYSt^ I <br />withdrawal was 10,779 gpd for _00 working days. estimated to have bean 74 acre (cct. <br />This decrease in usaCe can be auributed to com- <br />• <br />• <br />pletion of surface construction projects (water was <br />used for dust control, compaction, concrete pro- <br />duction, etc.). <br />Water from the freshwater pond(s) is used in two <br />ways. It can be treated to meet potable and sani- <br />tary water requirements, used, and then treated as <br />5anilarv waste water. Or, it can he withdrawn fur <br />dust suppression in the mine. in which case it then <br />becomes mine water. <br />Sanitary Waste Water <br />MCC's Mt. Gunnison pipeline water rights were <br />out of priority during a portion of water year 1991 <br />between July 28, 1992 and October 1. 1992. Aver- <br />age daily low Ilow in the North Furk during water <br />year 1992 was 347 cfs. The maximum wi[hdraw•al at <br />the intake is 450 gpm with both pumps operating. <br />This is about 0.3 percent of the ohserved average <br />daily low Clow in the river durims the water vcar. <br />The sanitary waste water treatment plant has been <br />operating since the fall of 1982. During water year <br />1992, discharge from the plant averaged 0.0043 cfs. <br />This discharge is approximately O.OOl2 percent of <br />the average daily flow of 347 cfs observed in the <br />North Fork during the year. <br />Discharge monitoring resulu from the waste water <br />treatment plant, conducted under NPDES Permit <br />No. CO-0038776, are included in Appendix J. <br />There were two isolated incidents of effluents <br />exceeding permit limitations. During monitoring <br />period 1 October - 31 December 1991. actual <br />residual chlorine reached 0.6~ vs. permit limitation <br />of 0.5; and during 1 July - 30 September 1992 <br />actual total suspended solids was 76.-1 vs. a permit <br />limitation of 4~. Both incidents appear to be <br />exceptions as the parameters were within limits at <br />all other times. Thc results of the analyses suggest <br />the waste water discharge has no measurable effect <br />on water quality in the North Fork Gunnison <br />River. <br />Mine Water <br />Mine inflows during water year 1992 were small. <br />The total mine water inflow was 68? acre (ect <br />during the year. The total water exiting the mine is <br />12 <br />The quality of mine +vatcr is considered good and <br />offers no problem for treatment and discharge. <br />Mine water was primarily discharged from the <br />Nu. 2 Portal. Nu discharees occurred from Svhes- <br />tcr Gulch or Portal No. 5. <br />Mine water inflow for water year 199± is expected <br />to be less than that cxpencnced during water vcar <br />1992. Onl_v the amount of water necessary for <br />mining will be imported imu the mine. Mine water <br />is expected ro have water quality characteristics <br />similar to that rcponed in Table ?. <br />Because of the small quantity of mine water <br />anticipated, any discharge from ponds would <br />normally be dominated by water quality character- <br />istics ofdisturbed area runoff as described in the <br />following section. <br />Runoff from Disturbed Area <br />Overland runoff from snowmclt and precipitation <br />within the disturbed areas is routed to one of six <br />sediment ponds on the mine site. The six sediment <br />ponds are designed to contain the predicted runoff <br />from a statistically determined 10 year. 24 hour <br />precipitation event as well as a Calculated sediment <br />storage volume. The ponds arc also designed to <br />pass the overflow from a 25 year, 24 hour precipi- <br />tation event safely. <br />The West Elk Mine site receives much of its <br />annual precipitation from snowfall during the <br />winter months. When warmer weather begins in <br />late February. March ur April, most runoff to the <br />sediment ponds is from snowmclt. h is entirely <br />possible for a volume of runoff greater than the 10 <br />year, 24-hour precipitation event to result from <br />snowmclt or snowmclt coupled with a small precip- <br />itation event. <br />The sediment ponds are treated with cationic <br />Ilocculent when necessarv to speed clarification <br />and settling of suspended solids. The ponds MB-l, <br />[v1B-2, MB-~. and MB-b have manually Controlled <br />dewatering devices. Ponds MB-3 and MB-1 hate <br />automatic dewatering capability. Ponds MB-I, <br />MB-'_, MB-~ and MB~i arc dewatered intermio- <br />tently with most discharges coming during early <br />spring runufl. Dewatcring procedures take usually <br />