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The Horse Gulch Fill will be re-topsoiled, and seeded in permanent vegetation <br />compatible with the planned post mining land use of Rangeland and Wildlife Habitat. <br /> <br /> As discussed below, the Division approved placement of the landslide material into the <br />Horse Gulch Fill. <br /> <br /> <br />1.The material to be moved from K Pit to the Horse Gulch Fill formerly overlaid the <br />coal seams; therefore, this material meets the definition of overburden (1.04(83)). <br />This overburden was removed during surface coal mining operations and, therefore, <br />also meets the definition of spoil (1.04 (122)). <br /> <br /> <br />2. <br />topography map (M12) demonstrates that the spoil overburden material proposed for <br />construction of the Horse Gulch Fill is not needed for achieving approximate original <br />contour; therefore, this material meets the definition of excess spoil (1.04(43a)). <br /> <br /> <br />3.The engineering designs for the Horse Gulch Fill are contained in Appendix T of the <br />permit application. The fills will be constructed entirely of excess spoil from the K- <br />Pit area. The spoil geochemistry of the K Pit is similar to spoil elsewhere in the <br />Trapper Maffected area. Neither coal mine waste (1.04(22a)), nor coal <br />processing waste (1.04(24)), will be used in the construction of the fills. <br /> <br /> <br />4.The Horse Gulch Fill is constructed in a valley where the side slopes of the existing <br />valley are greater than 20º, as measured at the steepest point; therefore, the Horse <br />Gulch Fill meets the definition of a valley fill (1.04(148)). The Horse Gulch Fill is <br />constructed in the uppermost reaches of a hollow where the sides of the gulch slope <br />more than 20 feet; therefore, the Horse Gulch Fill also meets the definition of a head- <br />of-hollow fill (1.04(56)). <br /> <br /> <br />5.An underdrain is constructed underneath the Horse Gulch Fill (Appendix T of the <br />permit application). The core of the underdrain was constructed in advance of <br />construction of the main spoil pile. The core was constructed of large rocks retrieved <br />from the toe of the main spoil area. All rock utilized for the underdrain had a diameter <br />between 12 inches and 60 inches. These design features demonstrate the underdrain <br />is constructed in compliance with 4.09.2(2). <br /> <br /> <br />6.Diversions of runoff around the Horse Gulch Fill are required by 4.09.3(1), based on <br />there being a significant difference between the elevation of the crest of the Horse <br />Gulch Fill and the low point of the adjacent ridgeline. Appendix T contains <br />engineering designs for diversion channels for the Horse Gulch Fill that meet the 100- <br />year, 24-hour storm event, as required by 4.09.2(7) for a valley fill and by 4.09.3(1) <br />for a head-of-hollow fill. <br /> <br /> <br />7.Appendix T of the permit application contains a slope stability analysis for the Horse <br />Gulch Fill utilizing a three-dimensional finite difference model. This analysis found <br />that horizontal lifts constructed by dumping material from a height of 400 feet will <br />result in a factor of safety for the Horse Gulch Fill of 1.45. The analysis also found <br /> <br /> <br />36 <br /> <br />Trapper MineJuly 9, 2013 <br /> <br />