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Brock Bowles <br />-2- May 22,2012 <br />west expansion. Also, the topsoil and cover volumes (cy) for the second, third & fourth 50 foot <br />bench and top of pile are incorrect. Please update these values. <br />BOW -2: Please see the revised total topsoil replacement volume as shown on Appendix A. <br />The topsoil and cover volumes for the second, third, fourth & top 50 foot benches are correctly <br />calculated in Excel. The calculations appear incorrect when calculated by hand due to rounding <br />differences. For example, the second 50 foot bench has an area associated with it of 5.06 acres, <br />in excel it is rounded to 5.1 acres. The third 50 foot bench has an area associated with it of <br />5.23 acres, in excel it is rounded to 5.2 acres. The fourth and the top benches have similar <br />rounding differences. Therefore, values shown for topsoil and coverfill replacement as shown in <br />Appendix A are correct and have not been revised. <br />Rule 2.05.3(8) and Rule 4.10 <br />5. DRMS: With TR -72, BRL is also proposing a modification to the shape of CMWDA No.2. <br />Previously, as shown on the current permit maps, the elevated central portion of the pile was <br />limited to a linear strip at the crest of the valley fill portion, parallel to the natural drainage. The <br />proposed configuration shows the flattened top of the pile extending westward, outside of the <br />valley fill area and onto the surface proposed for excavation. The "back side" of the pile crest <br />then drops away to the northwest, into West Diversion Ditch #2. In the Division's review of the <br />various geotechnical analyses that have been conducted for the Bowie No. 2 Mine, there is <br />nothing to demonstrate that this configuration, i.e. construction of the pile to elevations higher <br />than the catch point with the native slope, has been analyzed for stability. Please determine <br />the expected factor of safety for this configuration, ensuring that the requirements <br />of the Rule 4.10 performance standards will be met. <br />BOW -2: The most recent stability analyses for waste pile #2 was from September 22, 2008 <br />and based on assumptions made for the waste pile model, another stability analysis should not <br />be required. <br />The stability of the pile does not depend on the catch point of the native slope. As described in <br />Section 5.1 of the Geotechnical report, the Model Geometry for the stability analyses of the <br />waste pile takes into account the slope, the bench width, overall slope and ultimate waste pile <br />height. The proposed waste pile expansion to the west does not change the slope, the bench <br />width, the overall slope or the maximum height. <br />Further, Section 5.1 states "Stability of the coal waste bank was evaluated for the maximum <br />section, located through the approximate central portion of the waste bank...as shown on <br />Drawing 1 (Appendix A) ". The section shown in Appendix A does not take into account the <br />width of the pile, it is based, like the stability model parameters, on the slope, and ultimate <br />waste pile height. The representation of the 'maximum section' is a linear representation and <br />should not change based on the west expansion as the pile height and overall slope have not <br />changed. <br />6. DRMS: Figure 1 provides numerous cross - sectional views of the Coal Mine Waste Disposal <br />Area. Given the unique configuration proposed with TR -72, an additional cross section is <br />warranted. This section should be drawn approximately perpendicular to the West Diversion <br />Ditch #2, should intersect with (or terminate at) Section D -D', and should show the original <br />