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highest significant source of mine inflow, the Middle sandstone; consequently, mine <br />water will di scharge from the coal subcrops into the alluvium (rather than from the <br />alluvium to th.e subcrops). This discharge rate can be predicted to be a few gallons per <br />minute. Mine water is likely to seep from the coal outcrop where it is below 6300 ft. in <br />Sections 35 and 36 of T6N-R92W, in Section 6 of T6N-R91 W, and in Section 5 of <br />TSN-R91 W. <br />Potential for ,future leachate formation in workings from waste rock and materials. <br />Leachates can form in the sumped water as the water contacts rubblized waste rock and <br />abandoned materials. The main leachate-forming processes would be dissolution, <br />oxidation, cation exchange, and corrosion. The ultimate maximum concentration of <br />dissolved solids of mine water leachate is uncertain. The operator considered 1,474 mg/1 <br />as the maximum saturation level for TDS (page 8, 1992 annual hydrology report). This <br />level was base: on a several month period when pumping ceased and the concentration of <br />TDS in the mine water appeared to reach a plateau. (The TDS plateau also appeared to <br />coincide with a TDS plateau in the Trout Creek sandstone, the presumed water source.) <br />Other underground mine workings in Cretaceous-aged coal beds in Colorado having <br />alkaline mine water like the Eagle Mines have had TDS in the approximate range of 800 <br />mg/1 to 6,000 mg/1. The higher TDS occurred at one location (the Foidel Creek Mine) <br />where there is, an anomalously thick section of marine shale, and would not be expected <br />at the Eagle Mines based on local stratigraphy. Corrosion of old equipment in the <br />workings coulld add iron to the water, although the amount probably will be less than 1 <br />mg/1 (Table 2 in the hydrology evaluation memorandum). <br />Seepage of water from workings into unmined coal. Water sumped in the workings <br />probably will seep into coal beds in the walls of the workings along the downdip <br />(northern) margin of the workings, wherever enough head develops in the workings to <br />overcome the pore entry pressure of coal exposed in the walls. This seepage would occur <br />through small-scale fractures (cleat porosity) in the coal beds. Seepage would occur at a <br />rate on the order of less than 100 feet per year, based on a calculation of Darcy flow <br />(Table 1 in the hydrology evaluation memorandum). Vertical, cross-stratal seepage <br />through interg;ranular porosity in sandstones in the roof and floor of the workings is likely <br />to be negligiblle owing to low vertical permeability. <br />Potential for degradation of ground water in Middle Sandstone. Ground water is not <br />likely to flow from the workings to the Middle Sandstone through faults or fractures <br />because the hydraulic pressure in the Middle Sandstone is greater than the head that will <br />be produced by water sumped in the workings. Also, sumped mine water could not <br />migrate vertically to the Middle Sandstone through intergranular porosity because of low <br />vertical permeability in intervening beds. <br />Potential for degradation of ground water in alluvium of Williams Fork River and <br />Yampa River. Seepage of underground mine water is estimated to be less than 0.002 cfs <br />(see Table 1 in the hydrology evaluation memorandum). This seepage is likely to raise <br />TDS levels in alluvial ground water of the Williams Fork River a few mg/1. Other <br />