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11. The AAI Report on the HG Fill discusses inspection of construction of that fill and the <br />underdrain, but inspections are not mentioned in either the K-Pit Buttress stability analysis or <br />within the permit test. <br />Please provide specific information within the pages of the Permit that thoroughly addresses <br />the requirements of Section 4.09.1(11) regarding inspection of construction of the Horse Gulch <br />and K-Pit Buttress Fills. <br />12. Section 4.09.1(14) requires that the foundation and abutments of the fill shall be stable under <br />all conditions of construction and operation. Maps have been provided which depict the <br />mining plan and post-mining topography, and the method of construction of each fill is <br />described, e.g. dragline and/or truck dump. Very little information has been provided regarding <br />the anticipated phasing (including length of time required) for the dragline portion of HG Fill to <br />be constructed, or construction of K-Pit Buttress, or construction of the remainder of the HG <br />Fill. <br />Please provide additional detail about the timeline and phasing of the construction of the HG <br />Fill, in particular, including a discussion of the stability of the fill under all conditions of <br />construction and operation. <br />13. Section 4.09.2(2)(d) requires that in constructing the underdrains, no more than 10 percent of <br />the rock may be less than 12 inches in size and no single rock may be larger than 25 percent of <br />the width of the drain. Figure 24 and the Appendix A Horse Gulch Underdrain detail of the <br />AAI report indicate that no more than 10 percent of the rock will be less than 10 inches in size. <br />Please adjust the size from 10 inches to 12 inches for the underdrain material requirement. <br />14. For Model 3, AAI uses a highly weathered, slakable material, with fair compaction <br />(corresponding approximately to the last entry in Tables 5 and 7), in the analysis. The <br />estimated composition of the Horse Gulch Fill will be 40% shale and 60% sandstone (Table 6), <br />with high variability and segregation present throughout the fill. There may be no accurate way <br />to model for such variable composition, and AAI's stated approach is, "not to model for the <br />worst case but rather the worst reasonably expected case" (AAI, Page 9). Of the various <br />materials included in Tables 5 and 7, it appears to the Division that "Shaley material fair <br />compaction" may exist in the HG Fill in rather large proportion. The estimated cohesion for <br />this material is a mere 200 psf, and the Slope-W analysis predicted a failure surface occurring <br />in this layer rather than within the clay beneath. <br />Please provide a discussion evaluating the sensitivity (if any) of the proposed Horse Gulch Fill <br />to the possibility of as much as 40% of the volume of the fill being comprised of this un- <br />weathered shale material with fair compaction. <br />15. In the HG analysis, section 4.3 Drain Design, it is noted that a bulldozer will cut a trench along <br />the proposed alignment for the underdrain. According to the second paragraph on Page 20, <br />dragline spoil will be allowed to drape over the core to form the filter system. The drain design <br />details in Appendix A would seem to indicate that the core will be constructed of very coarse