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3) About one -half square mile of the Twentymile Sandstone will be undermined by <br />longwall mining in the E and F seams. Impacts to the Twentymile Sandstone <br />are very unlikely. No significant dewatering of the Twentymile is expected. <br />Twentymile water quality will not be impacted. It is unlikely any open fractures <br />will extend from the longwall areas up to the Twentymile Sandstone. <br />4) Mining in the 5 and 9 Mines will not significantly impact the only domestic <br />well near the permit area that may be completed in the Twentymile Sandstone <br />(Lux well). The predicted drawdown of this aquifer where the well is located <br />should not significantly impair the usefulness of the well, but it may require that <br />the pump be lowered. <br />5) During mining, mine dewatering discharge will cause a net increase in stream <br />flow in the Williams Fork River. <br />6) Underground mining in the Williams Fork Mines will not directly affect ground <br />water in the Williams Fork River alluvium. <br />7) Underground entries in the Williams Fork Mines that are beneath alluvium will <br />not directly affect ground water in the Yampa River alluvium. <br />8) Development mining beneath the Big Bottom alluvial valley floor of the Yampa <br />River will not impact the alluvial valley floor. <br />9) During mining of the 5 and 6 Mines, underground mine discharge from those <br />mines, combined with spoil spring discharge from the Strip Pit, will increase <br />dissolved solids concentration in the Williams Fork River. During low -flow of <br />the river and assuming worst -case mine discharges, the concentration will <br />increase by 224 mg/l, from the historical mean of 332 mg/1 to 576 mg /1. SAR <br />will increase from the historical mean of 0.44 to 5.05. The Williams Fork River <br />would have a medium salinity hazard during low flow, and would have a low to <br />moderate sodium hazard at other times. The worst -case discharges are not <br />expected to be reached based on past discharges; therefore, the medium salinity <br />hazard is not expected to be achieved. Impacts from dissolved solids loading of <br />the Williams Fork during irrigation season would be minimal due to dilution <br />resulting from high river stage. <br />10) After mining ceases or the mine pumps are temporarily shut off, the 5 and 6 <br />Mines will refill with water at about one -half the rate of the inflow rate during <br />mining. It is estimated that at the end of the life of the mine, it may take on the <br />order of 16 years for the mines to completely fill. At the writing of this <br />document, if the pumps are temporarily shut off, it would take about 8.6 years <br />for the currently mined area to refill. <br />11) After the 5 and 6 Mines refill, water may seep from the coal subcrop into the <br />Williams Fork alluvium. The seepage would be driven by a maximum pressure <br />developing in the subcrop equal to a head of 100 ft. above the ground surface. <br />This head would cause maximum seepage of 20 gpm. In a worst -case scenario, <br />Williams Fork Mines 24 Permit Renewal 06 <br />C- 1981 -044 December 8, 2014 <br />