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Wolf Creek Area <br />On September 25, 1984, the Division approved a permit revision for the Seneca <br />II Mine which allowed a change in the mine plan for the Wolf Creek pit area. <br />The Division findings regarding the backfilling and grading aspects of the <br />permit revision have been incorporated into this findings document and revised <br />as necessary to account for the resolution of stipulations attached to the <br />permit revision approval. <br />The proposed mining in the Wolf Creek permit revision area was found to result <br />in the generation of excess spoil as demonstrated in Table 12. Calculations <br />indicated that 1,855,000 yd3 to 2,380,000 yd3 of excess spoil would be <br />generated. The applicant used a swell factor of 19.8% based on actual <br />pre-mining and post-mining volumes using the STOCK computer program. The <br />excess spoil volumes were generated from a 148.58 acre area depicted in Figure <br />12-1 X. A fill was designed, approved, and is currently being constructed in <br />compliance with Rule 4.09.1(3). <br />An underdrain and a lateral drain to drain the seeps and <br />drainage were proposed. Drainage designs found in Table <br />measured and projected flow rates. Peabody Coal Company <br />that the drain would be constructed of natural sandstone <br />feet in diameter and that no more than 10 percent of the <br />than 12 inches in size. The applicant further stated th <br />free of coal, clay or shale. <br />springs within the <br />12 were based on <br />stated <br />rock no larger than 5 <br />rock would be less <br />~t the drains would be <br />The toe of the underdrain was designed to discharge into the coal seam and the <br />applicant stated that during wet periods the coal seam may not absorb all of <br />the underdrain flow. Ground water levels within the underdrain would rise and <br />then flow into the existing spoils, resulting in possible base saturation of <br />the existing spoils. The stability of the existing spoils was not addressed <br />in the revision application, and the Division determined that any discharge <br />which may result in base saturation should be alleviated or addressed in terms <br />of geochemical stability. The Division's field observations indicated that <br />there was an existing enclosed impoundment which exhibited swampiness in the <br />area where the drainage ended. This impoundment was located at the toe of the <br />proposed fill. Therefore, a stipulation was attached to the permit revision <br />approval requiring that, <br />"WITHIN 90 DAYS OF THE PERMIT APPROVAL THE APPLICANT SHALL SUBMIT AN <br />ADEQUATE DESIGN FOR A SURFACE DISCHARGING DRAIN TO BE CONSTRUCTED AT THE <br />TOE OF THE PROPOSED FILL. SHOULD THIS SURFACE DRAIN FLOW INTO AN <br />EXISTING SURFACE DRAINAGE SYSTEM THE APPLICANT SHALL DISCUSS THE EFFECT <br />ADDITIONAL FLOW WILL HAVE ON THE HYDROLOGIC SYSTEM." <br />Peabody Coal Company submitted the required designs within the 90 day <br />timeframe, thereby resolving the requirements of the stipulation. <br />The fill and drain were proposed to be constructed by dragline utilizing a <br />gravity segregation technique. The applicant committed to inspecting the fill <br />during construction, by a registered engineer or other qualified specialist at <br />least quarterly and during tfie required critical periods. However, because of <br />the type of dragline technique that would be employed to construct the <br />underdrain, the Division determined that inspections during the actual <br />-38- <br />