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The Wadge coal seam is separated from the overlying Twentymile sandstone by 700 feet of <br />massive shale and interbedded sandstones, siltstones, shales and coals. Overburden depths in the <br />current permit area range from 0 to 1,700 feet. <br />Surface Water Hydrology <br />The mine is located in the upper reaches of the Yampa River Basin. The permit area and <br />adjacent areas are drained by Foidel Creek, an intermittent stream, and Fish Creek and Middle <br />Creek, both perennial streams. Fish Creek drains east into Trout Creek whereas Foidel Creek <br />drains northeast to Middle Creek before Middle Creek joins Trout Creek. The quality of water in <br />the Fish Creek and Foidel Creek drainages have been affected previously by surface mining <br />upstream and downstream of the underground mine's existing surface facilities. Alluvial valley <br />floors are identified downstream of the mining area at the confluence of Foidel and Middle <br />Creek, and on Trout Creek from its confluence with Middle Creek downstream to the Yampa <br />River. Permit Revision No. 3 declassified portions of Foidel and Middle creeks previously <br />classified as AVF's. Detailed discussion concerning alluvial valley floors can be found in <br />Section B, part XVIII of this document as well as Exhibit 7j of the permit. <br />Ground Water Hydrology <br />The stratigraphy and geologic structure within the Twentymile Park Synclinal Basin control the <br />ground water flow within the permit and adjacent areas. There are three regional bedrock <br />aquifers within the permit and adjacent areas of the Foidel Creek underground mine. These <br />aquifers are the Trout Creek sandstone, the Twentymile sandstone, and the Wadge <br />coal-overburden zone. All three aquifers exhibit artesian conditions in central portions of <br />Twentymile Park Basin. The quality in all aquifers is moderately poor but is tolerable for use as <br />a drinking supply. <br />The geologic structure created by folding and faulting within the Twentymile Park Synclinal <br />Basin affects the direction of flow within the rock aquifers. In the permit and adjacent areas, the <br />direction of ground water flow in the bedrock aquifers is down dip toward the center of the <br />Twentymile Park Basin. Faults in the area produce localized fracture zones within the rock <br />strata. These zones of increased permeability increase the potential for vertical and horizontal <br />movement of ground water within the rock strata. However, experience to date in the Foidel <br />Creek Mine shows little to no inflow along the fault zones at the level of the Wadge coal seam. <br />Some inflows were encountered in 9 Right and 6 Right gateroads as they were developed into the <br />Eastern Mining District. These inflows appeared to be localized, and tapered off over time. <br />The Twentymile sandstone is separated from the underlying Wadge coal-overburden aquifer by <br />up to 700 feet of impermeable shale within the permit and adjacent areas. The underlying <br />700-foot shale and the overlying shales and siltstones of the upper Williams Fork Formation and <br />the Lewis Shale Formations produce the confined artesian conditions within the Twentymile <br />sandstone aquifer. To the northeast, the Twentymile sandstone recharges the alluvial aquifer and <br />provides base flow to the tributaries of Trout Creek down gradient of the mine. Salts in the <br />Twentymile sandstone waters are predominantly sodium bicarbonate and result in TDS levels of <br />150 mg/l. This aquifer is occasionally used for domestic needs. <br />F-oidel Creek Mine 9 June 4, 2010