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• below the 7350' level. Once [he water reaches this level, no significant hydraulic <br />gradient exists and the water moves at an imperceptibly slow rate. Overall, no <br />hydrologic impacts will occur. <br />2) The water reaches the 7350' level and begins entering the sandstone layer exposed in <br />the fault in the northwest part of the mine due to a hydrologic gradient into this aquifer. <br />This is the lowest elevation of the mine workings. As it enters this layer, it begins to <br />move in the general downdip direction of the strata, which is to the northwest. From this <br />point, the water would migrate toward a structural low which extends northward between <br />the Tow Creek anticline (on the west) and the Twen[ymile Park syncline (on the east). <br />In this path a narrow point exists in Section 13 of TSN-R87W and the movement rate <br />will likely slow from a rate of one inch per day to 0.1 inches per day or less. Assuming <br />that the movement rate becomes 0.1 inches per day, the mine water would cover an 8 <br />acre area in approximately 300 years. The 8 acre area is significant because [his is the <br />only area where water wells could be put into the sandstone layer with a depth of less <br />than 600 feet, which is considered maximum for economic wells of this area. Currently, <br />there are no wells completed in the sandstone layer in question. <br />The lack of wells in the area and the unlikelihood of future wells in [his particular <br />sandstone zone combined with the small plume area and the good water quality, it is a <br />remote possibility that this scenario could negatively impact [he groundwater of the area. <br />• 3) Water enters the mine to the 7350' level and seeps through the coal seam downdip to <br />the northwest. The same narrow point described in the scenario above exist for the coal <br />seam since the flowpath is nearly identical. the water could move very slowly through <br />the seam and along fracture planes in the coal. Again, velocities could be approximately <br />0.1 inches per day but could be much lower due to lower permeability of the coal seam <br />itself if fractures do not exist. Regardless, a plume would develop very slowly to the <br />northwest and would occupy 8 acres in 300 to 500 years, however, there would be no <br />impacts since no known wells of the area are drilled into the coal seam and, as <br />described above, the water quality is good. <br />The two main regional aquifers of the area, the Tow Creek sandstone and the Trout <br />Creek sandstone, will not be affected since they are they are a few hundred feet higher <br />and lower than the coal seam and are separated by shale zones of low permeability. <br />1) Potential of mine to affect surfacewater systems. <br />Trout Creek, a perennial stream of good water quality, flows immediately south of the <br />mine disturbed area. Since the mine portals are elevated 50 - 70 feet above the stream <br />• level and all workings are downdip of the portals, it is extremely unlikely that water <br />Mid-Term Review 3/21/01 190.4 <br />