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10. Division's Comment: Section 4.09.1(10) requires that where the slope in the disposal <br />area is steeper than 2.8h:1v (36 percent)... keyway cuts or rock toe buttresses shall <br />be constructed to stabilize the fill...AAI has identified steeper portions of natural <br />ground on the northern sideslopes of Horse Gulch and states that benching is <br />required for these areas ...Please provide a description of the benching activities <br />proposed for the steeper side slopes that exist within the Horse Gulch Fill area. <br />Trapper's Response: AAI's Horse Gulch Fill Stability Analysis report has been <br />revised to include a description of benching activities proposed for the steeper side <br />slopes that exist within the Horse Gulch Fill Area. This revised text can be found on <br />page 26 of the report, and Figure 29 of the report. <br />11. Division's Comment: The AAI Report on the HG Fill discusses inspection of <br />construction of that fill and the underdrain, but inspections are not mentioned in <br />either the K-Pit Buttress stability analysis or within the permit text. Please provide <br />specific information within the pages of the permit that thoroughly addresses the <br />requirements of Section 4.09.1(11) regarding the inspection of construction of the <br />Horse Gulch and K Pit Buttress Fills. <br />Trapper's Response: The inspection of fills is thoroughly addressed on the attached <br />permit text pages 340b and 340c. <br />12. Division's Comment: Section 4.09.1(14) requires that the foundation and abutments <br />of the fill shall be stable under all conditions of construction and operation... Very <br />little information has been provided regarding the anticipated phasing for the <br />dragline portion of the HG Fill to be constructed or construction of the K Buttress <br />Fill or construction of the remainder of the HG Fill. Please provide additional detail <br />about the timeline and phasing of the construction of the HG Fill in particular, <br />including a discussion of the stability of the fill under all conditions of construction <br />and operation. <br />Trapper's Response: Section 4.4 of AAI's revised Horse Gulch Fill Stability Analysis <br />report discusses the phasing of the construction of the Horse Gulch Fill, and <br />includes a discussion of the stability of the fill during construction and operation. <br />13. Division's Comment: Section 4.09.2 requires that in constructing the underdrains, <br />no more than 10 percent of the rock may be less than 12 inches in size and no single <br />rock may be larger than 25 percent of the width of the drain. Figure 24 and the <br />Appendix A Horse Gulch Underdrain detail of the AAI report indicate that no more <br />than 10 percent of the rock will be less than 10 inches in size. Please adjust the size <br />from 10 inches to 12 inches for the underdrain material requirement. <br />Trapper's Response: Figure 24 and Appendix A of the report have been revised to <br />reflect the 12 inch minimum rock size. <br />14. Division's Comment: For Model 3, AAI uses a highly weathered, slakable material, <br />with fair compaction in the analysis. The estimated composition of the Horse Gulch <br />Fill will be 40% shale and 60% sandstone with high variability and segregation