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<br />-1- <br />There are three regional bedrock aquifers within the permit and adjacent <br />areas of the Foidel Creek underground mine. These aquifers are the Trout <br />Creek sandstone, the Twentymile sandstone, and the Wadge coal-overburden <br />zone. <br />The Trout Creek sandstone underlies the Wadge coal seam and is separated <br />from the coal by 200 to 300 feet of interbedded shales, siltstones, <br />sandstones and coals within the pernit and adjacent areas, which act as <br />an aquitard for the artesian Trout Creek sandstone aquifer east of the <br />mine. The Trout Creek sandstone provides recharge to alluvial aquifer <br />and base flows to Trout Creek and its tributaries. The sandstone is an <br />important regional rock aquifer within the Twentymile Park Synclinal <br />Basin. It is used for industrial (mining), domestic, and irrigation <br />ground water supplies. <br />The Twentymile sandstone is separated from the Wadge coal-overburden <br />aquifer by up to 70U feet of impermeable shale within the permit and <br />adjacent areas. The underlying 70U-foot shale and the overlying shales <br />and siltstones of the upper Williams Fork Formation and the Lewis Shale <br />produce the confined artesian conditions within the Twentymile sandstone <br />aquifer. To the northeast, the Twentymile sandstone recharges the <br />alluvial aquifer and provides base flow to the tributaries of Trout Creek <br />downgradient of the mine. <br />The Wadge coal-overburden aquifer is composed of the coal seam to be <br />mined and the overlying interbedded and lenticular sandstones. This <br />aquifer has a combined permeability of 0.4 ft/day and an average porosity <br />of 0.2. The Wadge coal-overburden aquifer is confined and artesian. The <br />average gradient for the piezometric surface is 0.05 ft/ft as measured <br />from the Baseline Hydro]ogy Map, Map 9a with the permit revision <br />application. This aquifer provides approximately U.14 cfs (98 acre-feet) <br />of recharge to the alluvial aquifer and base flow of Fish Creek to the <br />northeast of the proposed mine. <br />The alluvia of Trout Creek and its tributaries are important sources of <br />ground water. The alluvial bodies are used as water supplies, provide <br />subirrigation to vegetation, and supply base flow to the streams. The <br />alluvial bodies are recharged by both the streams and the bedrock <br />aquifers. <br />The Foidel Creek alluvium in the area of the proposed Foidel Creek mine <br />is not, however, recharged by, nor does it discharge to, the adjacent <br />rock strata, as evident from vertical permeability tests conducted by the <br />applicant. The Fish Creek alluvial body is recharged by the bedrock <br />strata of the Williams Fork Formation four miles northeast of the <br />proposed mine. <br />The folding and faulting (geologic structure) within the Twentymile Park <br />Synclinal Basin affects the direction of flow within the rock aquifers. <br />In the permit and adjacent areas, the ground water flow in the bedrock <br />aquifers is down the dip of the strata into the Twentymile Park Basin. <br />Faults in the area produce localized fracture zones within the rock <br />strata. The zones of increased permeability, in turn, increase the <br />potential for vertical and horizontal movement of ground water within the <br />rock strata. <br />