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-38- <br />The North Fork region contains several historic, existing, or proposed waste <br />rock/coal refuse piles. The Mt. Gunnison Mine facilities includes a small one <br />acre waste rock pile with a larger pile of approximately 10 acres anticipated <br />in the future. The Orchard Valley Mine has an existing one acre waste rock <br />pile (1 acre) and a new pile that will cover several acres, and Western Slope <br />Carbon has recently reclaimed a small four acre waste rock pile. The Somerset <br />life-of-mine area includes two historic waste rock/coal waste disposal areas. <br />The Hubbard Creek site was used from 1970 until 1977. The East Yard site (9 <br />acres) was used as a waste dump prior to 1969, but is currently part of the <br />surface facilities area. All future waste rock at the Somerset Mine will be <br />disposed of underground, or at the waste disposal site established at the area <br />of the "C" seam mine portals (1.2 acres) after the final sealing of these <br />portals. <br />Most of these waste rock/coal refuse piles are located in areas away from the <br />North Fork, stream - alluvial aquifer system, and seepage could reach the <br />stream - alluvial aquifer system only after considerable dilution. Three <br />sites, however, the Somerset East Yard, and Western Slope Carbon's Crystal <br />Meadow and East Mine Bench sites are adjacent to streams, where seepage from <br />the piles wilt eventually enter the stream - alluvial aquifer system. <br />The effects of the waste piles on dissolved solids concentrations in the North <br />Fork of the Gunnison can be evaluated using the mass balance - mixing model <br />shown above. This requires estimating the total dissolved solids <br />concentration of the leachate from the pile and estimating the rate of <br />discharge to stream - alluvial aquifer systems. The total dissolved solids <br />concentration can be estimated by using a conservatively high concentration of <br />5,000 mg/1. This is the highest spoil water value seen in Colorado. The <br />chemistry of the leachate would probably be a sodium-bicarbonate, sulfate type <br />water with relatively low total metal concentrations and neutral pH. The rate <br />of discharge can be estimated from the water balance provided in the Orchard <br />Valley permit application. This water balance estimated subsurface flow to be <br />2.8 in/y r: Assuming that most of the water for subsurface flow and deep <br />seepage is the result of snowmelt, it may be that this discharge is limited to <br />n a 60-day period. The rate of discharge can be calculated. <br />\\X / ` ~ (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 />min/hr) - (60 sec/min) = 0.03 cfs day <br />Using an estimated concentration of 5,000 mg/1 and an estimated discharge of <br />0.03 cfs, the effects of the waste rock piles and mine water drainage upon the <br />North Fork of the Gunnison under average flow conditions can be estimated. <br />Cd (432 cfs)(95 m /1) + (0+25 cfs+(4:000 m /1) + (0.03 cfs)(5,000 m /1) <br />Cd = 97.6 mg/1 <br />