2009-05-22_GENERAL DOCUMENTS - C1981044

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3) About one-half square mile of the Twentymile Sandstone will be undermined by longwall mining in the E and F seams. Impacts to the Twentymile Sandstone are very unlikely. No significant dewatering of the Twentymile is expected. Twentymile water quality will not be impacted. It is unlikely any open fractures will extend from the longwall areas up to the Twentymile Sandstone. 4) Mining in the 5 and 9 Mines will not impact the only domestic well near the permit area that may be completed in the Twentymile Sandstone (Lux well). 5) During mining, mine dewatering discharge will cause a net increase in stream flow in the Williams Fork River. 6) Underground mining in the Eagle Mines will not directly affect ground water in the Williams Fork River alluvium. 7) Underground entries in the Eagle Mines that are beneath alluvium will not directly affect ground water in the Yampa River alluvium. 8) Development mining beneath the Big Bottom alluvial valley floor of the Yampa River will not impact the alluvial valley floor. 9) During mining of the 5 and 6 Mines, underground mine discharge from those mines, combined with spoil spring discharge from the Strip Pit, will increase dissolved solids concentration in the Williams Fork River. During low-flow of the river and assuming worst-case mine discharges, the concentration will increase by 224 mg/l, from the historical mean of 332 mg/1 to 576 mg/l. SAR will increase from the historical mean of 0.44 to 5.05. The Williams Fork River would have a medium salinity hazard during low flow, and would have a low to moderate sodium hazard at other times. The worst-case discharges are not expected to be reached based on past discharges; therefore, the medium salinity hazard is not expected to be achieved. Impacts from dissolved solids loading of the Williams Fork during irrigation season would be minimal due to dilution resulting from high river stage. 10) After mining ceases, the 5 and 6 Mines will refill with water at about one-half the rate of the inflow rate during mining, and it may take on the order of 16 years for the mines to completely fill. 11) After the 5 and 6 Mines refill, water may seep from the coal subcrop into the Williams Fork alluvium. The seepage would be driven by a maximum pressure developing in the subcrop equal to a head of 100 ft. above the ground surface. This head would cause maximum seepage of 20 gpm. In a worst-case scenario, the 20 gpm discharge would raise SAR in the Williams Fork River alluvial water from the historical mean of 3.6 to 9.4. The alluvial water is naturally higher in dissolved solids and metals than the mine discharge water; therefore, increased SAR is the only expected impact. Eagle Mine Complex 23 Permit Renewal 05 C-1981-044 May 22, 2009