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_ql_ <br />A complete water chemistry of this discharge has not been provided. <br />However, experience at other mining operations would suggest it to be a <br />sodium-bicarbonate, sulfate type water with relatively low trace metal <br />concentrations and neutral pH. <br />The North Fork region contains several historic, existing, or proposed <br />waste rock/coal refuse piles. The Mt. Gunnison Mine facilities <br />includes a small waste rock pile (1 acre) with a larger pile of <br />approximately 10 acres anticipated in the future. The Orchard Valley <br />Mine has an existing waste rock pile (1 acre), and Western Slope Carbon <br />has recently reclaimed a small waste rock pile (4 acres). The Somerset <br />life-of-mine area includes two historic waste rock/coal waste disposal <br />areas. The Hubbard Creek site was used from 1970 until 1977. The East <br />Yard site (9 acres) was used as a waste dump prior to 1969, but is <br />currently part of the surface facilities area. All future waste rock <br />at the Somerset Mine will be disposed of underground, or at a waste <br />disposal site to be established at the area of the "C" seam mine <br />portals (1.2 acres) after the final sealing of these portals. <br />Most of these waste rock/coal refuse piles are located in areas away <br />from the North Fork, stream - alluvial aquifer system, and seepage <br />could reach the stream - alluvial aquifer system only after <br />considerable dilution. Three sites, however, the Somerset East Yard, <br />and 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/y r. 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) - (60 days) - (24 hrs) - (60 <br />mine/h r) - (60 sec/mine) = 0.03 cfs day <br />