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Page 2 of 3 <br />Rule 4.10.4 Coal Mine Waste Banks — Construction Requirements <br />4. Coal Mine Waste Disposal Area No. 4, as constructed, differs in certain aspects from <br />the approved design. The TR -75 application recognizes that the height of the pile was <br />increased from 150 feet to 165 feet, and this change has been incorporated into <br />Buckhorn's stability analysis of the as -built configuration. It is not apparent, however, <br />that the new analysis closely considered the topographic differences between <br />Buckhorn's May 2009 design and what has actually been constructed. <br />The Division made manual measurements of the as -built topography (as provided on <br />Volume IX Figure 2 of the TR -75 application), and calculated the slopes at numerous <br />places across the face of the pile. As indicated above, the approved design assumed a <br />slope of 2.5H: IV for the lowermost 50 feet of the pile, below the first bench. For this <br />area, the Division found the slopes to range between 2.13 and 2.75, with an average of <br />2.36H:1V. For the area above the bench, the design assumed an overall slope of <br />3H: IV. As shown on the attached illustration, the overall slope (blue ink) appears to <br />range from 2.55 to 3.10, giving an arithmetic average overall slope of 2.85H:1 V. <br />Of greater potential concern than the overall slopes described above are the shorter <br />zones of much steeper slopes. Shorter segments of slopes were also spot- checked by <br />the Division; these are shown in red ink on the attached drawing. All locations <br />between 2.O1H:1V and 2.50H:1V are highlighted in yellow. Green -blue identifies <br />those locations where the slopes appear to be 2.00H:1V or steeper. The Division does <br />not know whether these discrepancies are sufficient to affect the factor of safety for <br />CMWDA4, but their existence should be acknowledged and considered in the as -built <br />stability analysis. Please revise the stability analysis for TR -75 to specifically address <br />the slope configurations that have been constructed for CMWDA4. <br />If you have any questions, please contact me. <br />Sincerely, <br />� <br />Susan L. Burgmaier <br />Environmental Protection Specialist <br />c: Bill Bear, Bowie Resources, LLC <br />Marcia Talvitie, DRMS <br />