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Table 5: Waste Pile Disposal Acrease in the North Fork <br />Area of Waste Disposal (Acres) bone <br />23.0 Hawk's Nest <br />22.0 West Elk <br />0.7 Bear No. Z <br />I0.8 Somerset/Sanborn Creek <br />4.0 Blue Ribbon <br />16.0 Bowie No. 1 <br />5.5 Bowie No. 2 <br />81.4 acres <br />(81.4 acres)(2.8 inches/year)(1/12) = 18.99 acre feet/year. <br />18.99 acre feet/yeaz = 827,204 ft'/yeaz; assume al] runoff within <br />60 days; therefore; 13,787 ft'/day = 574 ft'/hour = 10 ft'/minute = <br />0.2 ft'/second. <br />Leachate = 5,000 mg/l TDS. <br />The contribution of salts to leachate from existing and proposed waste piles along the North Fork of the Gunnison River would be <br />insignificant, relative to mine inflows, even if such runoff occurred during the 10-yeaz, 7-day flow (Table 6). Additionally, this is <br />probably an overestimation of the impact since seepage from piles is the result of snowmelt and would probably occur when stream <br />flows are much higher than average. <br />Table 6: Maximum Impacts Caused by Probable Minin¢ on the North Fork <br />,. of the Gunnison River Includine Proiected Waste Pile Runoff <br />Discharge (CFS) TDS (mgA) <br />Upstream (Q~) Downstream (Qa) Upstream (C~) Downstream (c~ <br />32.5 37.5 95 463 <br />47.6 52.6 95 357 <br />66.0 71.0 95 289 <br />432.0 437.0 95 127 <br />Subsidence Impacts on Surface Water Hvdrolo¢v <br />Subsidence caused by underground mining in the North Fork of the Gunnison Valley could modify [he local surface water hydrology. <br />These modifications can be divided into three categories: storage capacity or streamflow reduction; a change in the drainage basin <br />surface water hydraulics; and geomorphic impacts. These aze discussed in greater detail below. <br />The surface expression of subsidence fractures may impact the capability of a dam to hold water. Consequently, the Bowie No. 1 Mine <br />monitors the volume of water in stockponds located in affected areas and in areas projected to be affected. Two large reservoirs occur <br />within or on the life-of-mine ]ease boundary of the West EIk Mine. These are Minnesota (Monument) Reservoir and Beaver Reservoir. <br />Both are located below the outcrop of the F seam, and the portions of lower coal seams beneath these reservoirs are legally severed <br />from the (ease. Therefore, these two water bodies are not likely to be affected by mining. <br />16 <br />