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• 3) Unweathered Bedrock (Laramie-Overburden) Water Occurrence: <br />Overconsolidated clays and clay shales are the predominant lithology. No <br />Flows observed from these materials as permeabilities are very low and resist <br />vertical and horizontal migration of subsurface water from the overlying <br />weathered migration of subsurface water from the overlying weathered <br />bedrock. However, very isolated zones of silty, sandy rock types <br />representative of channel type environments may produce small quantities of <br />water (.5 gpm). The occurrence of water in the coal seam (thickness = 7 feet) <br />is restricted to the lower 1 ft. -2 ft., and appears only as visible surface <br />moisture. Subsurface water in the unweathered bedrock (thickness = 45 - 70 <br />feet) and the coal seam is considered to be confined and separate from one <br />another. <br />4) Laramie-Fox-Hills Aquifer Water Occurrence: Massive, fine grained sand and <br />siltstones. The No. 7 coal seam to be mined is separated by 100 to 200 feet of <br />Laramie clays and clay shales from the underlying Laramie and Foxhills <br />sandstone. Laramie-Foxhills aquifer will not be affected by the mining <br />operation. Thickness of this contoured aquifer is approximately 35 ft. <br />Geohydrology <br />Twenty-one existing wells were utilized by Colorado State University for the <br />• purpose of studying the geohydrology of the surficial, Laramie coal aquifer. In <br />addition, one well was constructed as part of a test de-watering effort of the fluvial <br />sand in the shop area and two wells were constructed into the Fox Hills Sandstone <br />to supply water for the project. The location of all wells in the study are noted in <br />Appendices I-1 and I-2. <br />Several types of aquifer tests were conducted on the test wells. The Ennis Draw <br />deposits possess transmissivities of 14,300 to 19,700 gpd/ft.; the Laramie shale <br />overburden, 2.5 to 34 gpd/ft.; the coal, 1.8 to 236 gpd/ft.; and the Fox Hills <br />Sandstone, 1,630 to 2,340 gpd/ft. (See Appendix I, McWhorter, page 18). <br />Aouifer Extent and Piezometric Surface <br />All the above described aquifers with the exception of the Ennis Draw fluvial <br />subsurface water system are present under the entire area of the proposed B-pit <br />project site. The blow sand and fluvial sand thickens eastward across the project <br />to its greatest thickness in Ennis Draw. The bedrock aquifers are relatively <br />uniform in thickness and dip westward into the Denver Basin. <br />• <br />49 <br />