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-17- The deepest sandstone, the Sego of the Iles Formation (Collins, 1976) pinches out from a maximum thickness of 40' near Piceance Gap (northwest of the minesite) toward New Castle to the southeast. The Trout Creek sandstone, in the upper portion of the Iles Formation, lies approximately 800' above the Sego, and consists of 50' - 145' of silty, calcite-cemented, massively bedded buff to white sandstone. The overlying Williams Fork Formation contains numerous predominately non-marine sandstones, interbedded with siltstones, coals, claystones and shales. The Wheeler is generally considered the lower-most coal of the Williams Fork Formation in the area. The E-Seam to be mined within this permit term, lies within the upper-most portion of the Iles Formation. Together, these seams lie within the lower 1200' of the Mesa Verde Group, stratigraphically covered by 3700' of interbedded sediments. The low permeability of these interbedded units effectively isolates the coal seams from shallow groundwater south of the Grand Hogback. Three domestic wells have been completed in the shallow bedrock aquifers of the area. These wells have been drilled in the Upper Williams Fork Formation. The Gamber well is located approximately 7 miles southeast of the mine site. The Becker Well is located approximately one mile southwest of the life-of-mine permit boundary and three miles southwest of the five year permit term. Both of these wells, from the indicated depth of completion, appear to tap the uppermost sandstone units of the Williams Fork Formation. The Seivers well is located approximately 2.5 miles southeast of the portal area, and 1.5 miles south of the life-of-mine permit boundary. This well has a total depth of 55'. This well is located only 1/4 mile south of the outcrop of the Wheeler Seam. However, due to the extreme dip in the area, the well is separated from the seam by several hundred feet of low permeability units. The proposed mining operation will not impact these wells as, at a minimum, the producing unit will be separated from the coal seams by Z00 feet of low permeability units. There are numerous alluvial wells south of the permit area along the Colorado River. The alluvium thickness is projected to be up to 87 feet. The ground water provides domestic and livestock water for 26 wells in the vicinity of the mine site. Water yields of these alluvial wells range from 2 to 50 gpm. Alluvial aquifer potential also exists along the Elk Creek Drainage north of the Grand Hogback. This alluvium is perched on Mancos Shale and is isolated from the coal seams at the Eastside Mine by this impermeable unit. The alluvium fringing the Colorado River is separated from the Mesa Verde Formation by relatively impervious units of the Wasatch Formation. There is the potential that surface water impacted by mining operations at Eastside could impact the quantity and/or quality of water within the Colorado River alluvium. This potential impact is further addressed later in this section.