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the low permeability of the strata between the pit and the underground mine <br />workings will minimize the handling of degraded spoils waters by 1) <br />lengthening the flow path between spoils and mine, 2) lowering the flow rate, <br />and 3) eliminating the need to dewater the spoils aquifer. <br />The salt plume from the adjacent spoils aquifer nevertheless has had an <br />influence on the quality of mine inflow water. As distance into the mine has <br />increased, water quality has improved. The electrical conductivity of inflows <br />(as evident in Map No. 35) decrease toward the back of the mine. Near the <br />portal, EC's of inflows average near 4000 umhos/cm and in the northwest <br />portion of the mine inflows have been measured at 730 umhos/cm. The <br />differences in conductivity are a result of down dip migration of surface <br />spoils leachate water between the clay highwall and the mine workings. The <br />water quality of inflows are expected to improve as the mine advances. <br />After the mining operations have ceased at the Foidel Creek underground mine, <br />degraded mine and spoils waters will enter 1) the rock strata affected by <br />mining (i. e., the coal, floor, ar•J roof strata in the zone of subsidence), and <br />2) the fault and fracture systems encountered during mining. The underground <br />mine, upon cessation of mining, will contain fractured roof and coal strata, <br />and exposed floor strata. Also, the mine inflows will continue until the mine <br />workings are filled, and an equilibrium is reached between the mine inflow <br />rate and the discharge rate through affected strata, faults and fractures. <br />The inflow waters will pick up soluble ions due to the leaching and weathering <br />of the exposed and fractured rock strata. Some of the inflow water will be <br />spoils waters from the adjacent Mine No. 1 and Eckman Park Mines, which mined <br />the Wadge coal seam by surface methods and which have the same exposed strata <br />at their northernmost (down dip) limit. The increased permeability of the <br />abandoned underground mine workings will tend to move the point source of <br />degraded mine and spoils waters down dip, closer to the center of the <br />Twentymile Park Synclinal Basin and closer to the discharge points of the <br />affected strata, faults and fractures. The recovery of the potentiometric <br />levels of the overburden aquifer is expected to take 350 years. Migration of <br />poorer quality mine water off site is not expected to occur until this time. <br />Based on leachate tests and ground water flow rates of 12.3 acre-feet per year <br />for the workings it is expected that it will take at least 3000 years for the <br />ground water TDS to start declining significantly and 5000 years to return to <br />base line. When the leachate plume reaches the discharge area at Fish Creek <br />it is expected to discharge at a rate of about 54 gpm. The applicant <br />calculates that discharge should begin to occur 110 years after the <br />potentiometric levels reestablish or about 460 years after mining. The <br />addition of 54 gpm of poorer quality mine water to Fish Creek will not <br />significantly impact the water quality of the creek. <br />Surface Water <br />The applicant has provided a discussion of the probable hydrologic <br />consequences of the proposed operation to the surface water hydrologic <br />system. Several possible effects on the surface water system have been <br />identified: <br />1) increased salt loading in streams draining the proposed permit area; <br />-43- <br />