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foot bench and top of pile are incorrect. Please update these values. <br />Rule 2.05.3(8) and Rule 4.10 <br />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. <br />The proposed configuration shows the flattened top of the pile extending westward, outside <br />of the valley fill area and onto the surface proposed for excavation. The "back side" of the <br />pile crest then drops away to the northwest, into West Diversion Ditch 92. In the Division's <br />review of the various geotechnical analyses that have been conducted for the Bowie No. 2 <br />Mine, there is nothing to demonstrate that this configuration, i.e. construction of the pile to <br />elevations higher than the catch point with the native slope, has been analyzed for stability. <br />Please determine the expected factor of safety for this configuration, ensuring that the <br />requirements of the Rule 4.10 performance standards will be met. <br />6. Figure 1 provides numerous cross - sectional views of the Coal Mine Waste Disposal Area. <br />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 />ground surface, the limits of excavation proposed, any CMW that is presently in- place, and <br />the proposed final limits of CMW placement. <br />Rule 4.05.6(3)(a) <br />7. The revised Sedcad modeling provided by Bowie Resources, LLC (BRL) indicates that the <br />additional disturbance created with the gob pile expansion will result in increased runoff to <br />Pond F. Accordingly, the sediment storage of the pond must be reduced by half to <br />accommodate the additional runoff volume. BRL has revised the model assuming there will <br />be one year of sediment storage, down from the original plan for two years' storage. In <br />reviewing the quarterly sediment pond reports provided by BRL since Pond F was <br />constructed, BRL has reached the maximum sediment capacity and been required to clean <br />Pond F annually. If BRL increases the disturbed area and subsequent runoff volume as <br />predicted in the proposed gob pile expansion plan, BRL would need to clean the pond on <br />average every six months. The Division is concerned that this increased frequency may not <br />be manageable long term, and is inconsistent with Rule 4.05.6(3)(a), requiring "... adequate <br />sediment storage volume and periodic sediment removal to effect compliance with Rule <br />4.05.2(7)." BRL should consider options for increasing the volume of the pond. <br />Rule 4.05.6(4) and 4.05.9(2) <br />8. Page App. B -7, the flow characteristics for the Pond F Steel Flume, shows a side slope of <br />1.5:1. The currently approved design shows aside slope of 0:1, which is consistent with the <br />currently installed flume. Please revise the design to reflect the existing side slopes of 0:1. <br />9. Also on page App. B -7, the required peak discharge is listed as 35.52 CFS. The Sedcad run <br />shows a peak discharge of 54.47 CFS. Please also revise this figure to 54.47, as shown in the <br />Sedcad model output (page App. B -40). <br />Page 12 <br />