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Locally significant are the rock units of Twentymile Park Basin which dip ~' - 30' toward the central portion of the basin. Normal faulting has been identified throughout the permit area. striking generally northwest to ;:xr,'cea;:...i.h disrlxe-ec[ o[ ze:e ,o v fee:..~ reverse fault r~nnin~ in an arc :are line r+.erhward through the west central part of the basin shows displacement of U-$v ;cc:. ~,:.a.~=; iate:ai fac.., .sere encoun[e:ec i; the 9R and I OR gateroads while driving development out into the Eastern ivlining District. The near-surface bedrock units are composed of sedimentary rocks of marine and non-marine origin. These sedimentary rocks were formed through the transgression and regression of an epicontinental sea and are comprised of sequences of sandstones, siltstones, shales and coal. Four geologic formations exist in the vicinity of the Eastern Ivtining District. They are, in ascendins order, [he Ivtancos Shale, the Iles and Williams Fork Formations of the Ivlesaverde Group, and the Lewis Shale. These strata were all deposited during the late Cretaceous Period. Generally, the strata dip to the center of [he basin at about 7°. Three economically important coal seams, the Lennox, Wadge, and Wolf Creek coals, are located within the locally important [vtiddle Coal Group of the Williams Fork Formation. At this time, the Wadge coal seam is the only seam being mined in the Foidel Creek underground mine. The Wadge Coal seam was strip mined in CYCC's adjacent Energy No. I and Eckman Park Mines (No. C-81-071) and Energy Mine No. 3 (C-84-062). The Wadge coal seam, in the area of [he Foidel Creek Mine, is separated from the underlying Trout Creek sandstone by about 250 feet of interbedded sandstones, siltstones, shales and coals. The Wadge coal seam is separated from the overlying Twentymile sandstone by 700 feet of massive shale and interbedded sandstones, siltstones, shales and coals. Overburden depths in the current permit area range from 0 to ],700 feet. The stratigraphy and geologic structure within the Twentymile Park Synclinal Basin control the ground water flow within the perntit and adjacent areas. There are three regional bedrock aquifers within the permit and adjacent areas of the Foidel Creek underground mine. These aquifers are the Trout Creek sandstone, the Twentymile sandstone, and the Wadge coal-overburden zone. All three aquifers exhibit artesian conditions in central portions of Twentymile Park Basin. The quality in all aquifers is moderately poor but is tolerable for use as a drinking supply. The geologic structure created by folding and faulting within the Twentymile Park Synclinal Basin affects the direction of flow within the rock aquifers. In the permit and adjacent areas, the direction of ground water flow in the bedrock aquifers is down dip toward the center of the Twentymile Park Basin. Faults in the area produce localized fracture zones within the rock strata. These zones of increased permeability, in turn, increase the potential for vertical and horizontal movement of ground water within the rock strata. However, experience to date in the Foidel Creek mine shows little to no inflow along the fault zones at the level of the Wadge coal seam. Some inflows were encountered in 9R and 6R gateroads as they were developed into the Eastern Mining District. These inflows appeared to be localized, and tapered off over time. The Twentymile sandstone is separated from the underlying Wadge coal-overburden aquifer by up to 700 feet of impermeable shale within the permit and adjacent areas. The underlying 700-foot shale and the overlying shales and siltstones of the upper Williams Fork Formation and the Lewis Shale Fotma[ions produce the confined artesian conditions within the Twentymile sandstone aquifer. To the northeast, the Twentymile sandstone recharges the alluvial aquifer and provides base flow to the tributaries of Trout Creek down gradient of the mine. Salts in the Twentymile sandstone waters are predominantly sodium bicarbonate and result in TDS levels of I50 mg/I. This aquifer is occasionally used for domestic needs. The alluvia of Trout Creek and its tributaries are important sources of ground water. The alluvial bodies are used as water supplies, provide subirrigation [o vegetation, and supply base flow to the streams. The alluvial bodies are recharged by both the streams and the bedrock aquifers. C:\JHB\C82056\PRO5\PR05 FINDINGS 62800.doc 7