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State Req. <br />i. Geologic Relationships • <br />Aquifer thickness may vary slightly throughout the permit area and is a <br />principle factor in controlling water quantity. Maximum average thick- <br />nesses for aquifers identified eorlier•in this section are as follows: <br />Aquifer Thidcness(Feet) <br />Trout Creek Sandstone 120 <br />Wadge Overburden 50-55 <br />Wodge Coal Seam 9-10.5 <br />Alluvium 40 Feet or Greater <br />Reclaimed Spoil 115 (Maximum) <br />The thickness of alluvium and spoil materials may vary significantly <br />owing to the nature of deposition and placement. <br />Most aquifers are laterally continuous downdip from their outcrops, with <br />the exception of several localized "windows" in the Wadge and Wolf <br />Creek coal seams. These 'tivindows" refer to areas in the overburden <br />where erosion has exposed the underlying coal seam. Examples of these <br />windows in the Wadge coal seam are evident in the southern part of the <br />permit area and ore shown in Exhibit 7-2. In general, horizontal extent <br />of aquifers is greater for older strata than younger strata due to geologic <br />structure (anticline) and resistance to erosion. <br />Geologic structure, to a great extent, controls the prevai ling direct ion of <br />ground wafer flow in the mine plan area. Structural highs (Tow Creek <br />Anticline) act as ground water divides and recharge areas; whereas <br />structural lows (synclines) and alluvium act as areas for ground water <br />discharge. Fwlts in the vicinity of the mine act as barrier boundaries. <br />These areas are shown on Exhibit 7-2. <br />Ground water recharge for aquifers in the mine permit occurs at au?- <br />crops as shown in Exhibit 7-2. In these areas, the ground wafer is under • <br />water table conditions. Aground water flows downdip from recharge <br />areas, saturation thickness increases until an impermeable layer, such as <br />7-44 <br />Revised 5/27/81 <br />