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• 2.7.5.1 a Aquifer Characteristics <br />Ground water at the Trapper Mine site occurs in both bedrock and alluvial aquifers. The geologic units of <br />importance to this study are the Twentymile Sandstone, the Upper Unit of the Williams Fork Formation, the <br />Lewis Shale, and the Yampa River and local alluvial aquifers. The Twentymile Sandstone is the major <br />bedrock producing aquifer in this area. <br />Figure 2.7 -18p shows the intervals selected to define the different hydrologic units above the Twentymile <br />Sandstone. The lowest coal seam to be mined at Trapper is the R seam. The sandstones and associated U <br />coal seams below the R seam have been labeled the U aquifer. The Q and R seams and permeable material <br />between these two seams have been termed the QR aquifer. Some sandstones normally exist between the <br />KLM sequence of coal seams and has been labeled the KLM aquifer. The H and I coal seams are typically <br />mined together and have been combined as the HI aquifer. The Third White Sandstone exists between the G <br />and H coal seams and is called the Third White Sandstone aquifer. The uppermost bedrock aquifer of <br />importance to the Trapper Mine is the Second White Sandstone. The Lewis Shale exists above the Second <br />White Sandstone in the Pyeatt drainage and alluvial aquifers overlie different units depending on location. <br />• The following sections discuss each of these hydrogeologic units which are significant to this study. This <br />section presents well completions, aquifer descriptions, aquifer coefficients and similar information for each <br />aquifer unit. Table 2.7 -20 presents the basic well data for wells at the Trapper Mine. Baseline conditions <br />have been measured at each of these sites for at least the last year. <br />2 -462a <br />t= nr' --zrS <br />