2013-09-20_REVISION - C1981019 (2)

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prevent seam interaction effects, no potential impacts will occur on future G78 panels. 2. AA recommends avoiding the previously mined E Seam highwall miner workings when designing the F Seam panels. Does Colowyo plan on avoiding the previously mined E Seam highwall miner workings when designing the F Seam panels as recommended by AA? Response: Yes, Colowyo will avoid the previously mined E Seam highwall miner workings when designing the F Seam panels as recommended by Agapito Associates (AA). Map 23 has been revised to clearly show this plan change (see enclosed Map 23). 3. When reviewing the proposed highwall mining section in the North End Wall in the South Taylor pit, the maximum penetration distance appears to undermine a section of the temporary East Taylor Fill. In AA's geotechnical assessment, web pillars are designed based upon a range of design depth of cover. It is unclear to the Division it (sic) the temporary section of the East Taylor Fill has been incorporated into the total depth when calculating web pillar widths. Please address whether the temporary section of the East Taylor Fill has been accounted for in AA's proposed web pillar design and whether potential web pillar failure would have any adverse effect to the East Taylor Fill. Response: The Division is correct that maximum penetration distance for proposed highwall mining in the North End Wall in the South Taylor Pit may undermine a section of the temporary East Taylor Fill. The temporary section of the East Taylor Fill will be incorporated into the total depth when calculating web pillar (and barrier pillar) widths. To ensure that the AA "Web Pillar (and Barrier Pillar) Design Chart — South Taylor Pit G7 and G8 Seams" design chart information (pages 39 — 41) contains sufficient Design Depth of Cover vertical depth, these Charts have been redone to expand the vertical range from 460 feet to 580 feet. Enclosed, please find a new copy of the entire AA report with the revised pages inserted. Colowyo will employ AA's web and barrier pillar design charts for the final web and barrier pillar designs to ensure long term stability of the temporary East Taylor Fill. By utilizing the AA's design criteria, no adverse effects (subsidence) are expected to occur in any area that Colowyo performs highwall mining. Therefore, no adverse effects will occur to the Temporary East Taylor Fill. 4. Reviewing lithology logs for selected boreholes, multiple seams that are proposed to be mined have carbonaceous mudstone /mudstone as the immediate roof, floor, or both. AA states in their report that previous A anining property of Western Fuels- Colorado, A Limited Liability Company