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9 • <br />AQUIFER CHARACTERISTICS <br />Five aquifers of potential significance have been identified at the Seneca II mine. <br />These aquifers are listed below in their order of relative importance: <br />1. Trout Creek Sandstone <br />2. Wadge Overburden <br />3. Wadge Coal Seam <br />4. Alluvium <br />5. Reclaimed Spoil <br />The stratigraphically higher Twenty Mile sandstone member outcrops in the adjacent <br />area West of the permit boundary and will not be disturbed by mining activities. <br />Major aquifers such as the Twenty Mile and Trout Creek sandstones are markedly more <br />significant areally than middle coal group aquifers because of their thickness, <br />continuity, and water yielding ability. Middle coal group aquifers are, therefore, <br />considered to be important only in areas where the Twenty Mile sandstone is absent <br />or unsaturated (outcrops) and drilling costs to reach the Trout Creek are prohibitive. <br />Such areas comprise an almost insignificant portion of the general area. <br />The Lennox coal seam and overburden are dry in all areas of the permit area and are <br />not considered to be aquifers based on past drilling experience. However, these <br />strata are important hydraulically because they comprise the impermeable confining <br />layers overlying the Wadge overburden aquifer. <br />Aquifer thickness may vary slightly throughout the permit area and is a principle <br />factor in controlling water quantity. Maximum average thicknesses for identified <br />aquifers are as follows: <br />Aquifer <br />Trout Creek Sandstone <br />Wadge Overburden <br />Wadge Coal Seam <br />Alluvium <br />Reclaimed Spoil <br />Thickness (Feet) <br />170 <br />50-55 <br />9-10.5 <br />40 feet or Greater <br />115 (Maximum) <br />The thickness of alluvium and spoil materials mau vary significantly owing to the <br />nature of deposition and placement. <br />Most aquifers are laterally continuous down dip from their outcrops, with the <br />exception of several localized "windows" in the Wadge and [JOlf Creek coal seams. <br />These "windows" refer to areas in the overburden where erosion has exposed the <br />underlying coal seam. Examples of these "windows" in the Wadge coal seam are <br />evident in the southern part of the permit area. In general, horizontal extent of <br />aquifers is greater for older strata than younger strata due to geologic structure <br />(anticline) and resistance to erosion. <br />