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-44- <br /> <br />Western Slope Carbon's Crystal Meadow and East Mine Bench sites are <br />adjacent to streams, where seepage from the piles will eventually enter <br />the stream - alluvial aquifer system. <br />The effects of the waste piles on dissolved solids concentrations in <br />the North Fork of the Gunnison can be evaluated using the mass balance <br />- mixing model shown above. This requires estimating the total <br />dissolved solids concentration of the leachate from the pile and <br />estimating the rate of discharge to stream - alluvial aquifer systems. <br />The total dissolved solids concentration can be estimated by using a <br />conservatively high concentration of 5,000 mg/1. (This is the highest <br />spoil water value seen~in Colorado.) The chemistry of the leachate <br />would probably be_ a sodium-bicarbonate, sulfate type water with <br />relatively low total metal concentrations and neutral pH. The rate of <br />discharge can be estimated from the water balance provided in the <br />Orchard Valley permit application. This water balance estimated <br />subsurface flow to be 2.8 in/yr. Assuming that most of the water for <br />subsurface flow and deep seepage is the result of snowmelt, it may be <br />that this discharge is limited to a 60-day period. The rate of <br />discharge can be calculated. <br />(13 acres surface area) x (2.8 in.) x (1/12) = 3 acre-feet water. <br />(3 acre-feet) x (43,560 ft3/acre-feet) - (6Q•days) - (24 hrs) - (60 <br />mine/hr) - (60 sec/mine) = 0.03 cfs day <br />Using an .estimated concentration of 5,000 mg/1 and an estimated <br />discharge of 0.03 cfs, the affects of the waste rock piles and mine <br />water drainage upon the North Fork of the Gunnison under average flow <br />conditions can be estimated. <br /> <br />Cd = 97.6 mg/1 <br />This results in a 2.6 mg/1 increase over baseline conditions, which <br />is insignificant. In addition, it is probably an over estimation, <br />since seepage in the piles is the result of snowmelt and would <br />probably occur when stream flows are much higher than average. <br />Natural faults and fractures, as well as fractures caused by <br />subsidence; could reduce streamflow by directly diverting surface <br />flow and alluvial ground water into the bedrock ground water <br />system. This effect is undesirable both because of the hydrologic <br />effects and the mine operation problems it could induce. <br />Experience with underground mines throughout the state, as well as <br />in the North Fork area, indicates that mine inflows are not <br />normally significant when ephemeral streams are undermined. Most <br />of the streams to be undermined in the region are ephemeral and <br />would not be expected to be significantly affected by mining. Flow <br />t <br />