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<br />Inflows from faults and fractures located outside stream valleys (such <br />as in the Orchard 4alley Mine) generally dry up with time or flow <br />intermittently at discrete points along the fault or fracture. Those <br />which continue to flow have flow rates which diminish to a trickle. <br />Such inflows may represent the dewatering of lenticular sandstone units <br />with limited recharge areas, or may represent flows through fracture <br />zones extending to the surface which have narrow recharge zones on steep <br />slopes. <br />Description of the Surface Water Regime <br />The North Fork of the Gunnison River is the major drainage for the <br />general area. Smaller streams in or adjacent to the life-of-mine areas <br />are all tributary to the North Fork (Figure 2). Figure 3 contains the <br />drainage map of the study area with the locations of streams and <br />reservoirs which are described in the following discussion. <br />The North Fork has an annual streamflow at Somerset of approximately <br />313,200 acre-feet per year (1933-1982). The flow is regulated by the <br />Paonia Reservoir 5 miles upstream of the town of Somerset, which became <br />operational in 1962. Water yields during that period have ranged from a <br />high of 451,300 acre-feet per year in water year 1962 to a low of 82,270 <br />acre-feet in water year 1977. Flow records for the North Fork of the <br />Gunnison are given in Table 4. Annual streamflow for water years <br />1983-1985 was significantly higher averaging 580,800 acre-feet per <br />year. Annual streamflow was highest in 1984 with 601, 800 acre-feet per <br />year. Water quality parameters for the North Fork are given in Table <br />3. As indicated, water in the North Fork is a calcium bicarbonate <br />type. There are moderate levels of sulfate. Salinity averages less <br />than 100 mg/1. <br />Just below Paonia Reservoir, Muddy Creek and Anthracite Creek join to <br />form the North Fork of the Gunnison. Anthracite Creek contributes about <br />two-thirds of the flow to the North Fork. Anthracite Creek is a <br />perennial stream with an average annual yield of 157,313 acre-feet for <br />the period of record between July, 1977 to October, 1980 (U.S.G.S., <br />Water Research Data). This corresponds to an average flow rate of 217 <br />cfs. The highest discharge recorded was 4,200 cfs on May 27, 1979. Low <br />flows of 12 cfs have been recorded several times during the period of <br />record. <br />The water of Anthracite Creek is an alkaline, moderately hard, <br />calcium-bicarbonate type water with an average total dissolved solids <br />concentration of 71.6 mg/1, average pH is 7.8. Total suspended solids <br />average approximately 25 mg/1. Dissolved metal concentrations are low <br />throughout the year, and total metal concentrations are directly related <br />to the total suspended solids concentrations. <br />38 <br />