Laserfiche WebLink
_, <br />` _, <br />. ,.~ <br />Predecisional Draft ~~~~~'~12/28/94 <br />Kerr Coal Company -Man Strip ., <br />motorgraders would be used to construct the final surface except where <br />specific slope conditions create a safety hazard. <br />At the Kerr tipple area, a surface facility only, the extent of final grading <br />would be minimal. The area has little topographic relief and is proposed to be <br />graded, using bulldozers and motorgraders, along the contour. <br />Swell Factors and Supporting_Calculations <br />A volumetric swell factor for design purposes has been estimated at 24 <br />percent, based upon field and laboratory testing and past operational <br />experience. The testing, which was done to determine the swell factor, <br />consisted of measuring the density of undisturbed materials and materials in <br />the existing spoil. No details were provided regarding that past operational <br />experience alleged to substantiate a 24-percent swell factor. <br />Kerr Coal Company proposes to continue its present practice of aerial <br />volumetric surveying to determine that a mass balance of backfilled <br />overburden is maintained. This survey should provide data for adjustment of <br />the swell factor as mining proceeds. <br />A 24-percent swell factor is probably high, as the Sigma Mine, located just <br />south of Marc Strip Mine, has determined a swell factor of 17 percent through <br />operational experience. Refinement of the design swell factor at Man Strip <br />Mine must occur based on further information to be collected. <br />Postmining Topography <br />The disturbed ground surface is to be returned to approximate original <br />contour. Though the ground level is projected to be higher in the existing pit <br />and Pits 1 and 2 after backfilling, it is to be blended around the perimeter to <br />assure that no abrupt changes occur. Pit 3 has a proposed average decrease in <br />elevation of approximately four feet. Map 37a, the Ken Mine Area <br />Postmining Topography, depicts the planned postmining topography and snows <br />[shows] proposed final slopes. <br />Compared to Map 34a, Ken Mine Area Premining Topography, the planned <br />postmining contours are very similar to the existing topography and the <br />postmining slopes are equal to or less than the premining slopes. A maximum <br />2 <br />