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fill. In a phone call on March 31, 2009 with Trapper Mine personnel, the Division discussed <br />possible changes to the drainage design for Horse Gulch Fill to incorporate 100-year channels <br />to meet the requirements of 4.09.2(7). Also discussed was utilizing two riprap downdrains as <br />recommended by the Agapito Report, rather that the single north downdrain as shown on the <br />Trapper Figure T-1. <br />Should these changes be implemented, please provide revised surface drainage calculations, <br />including SEDCAD design information. <br />8. Table 4.9-3 reflects the projected bank cubic yards of topsoil to be salvaged and replaced; <br />however, the K-Pit area, Horse Gulch Fill and K/G Buttress Fill are not included with the costs <br />associated with tables 1.4-8 and 1.4-9 which provide a summary of topsoil replacement costs <br />for the Trapper Mine. Please acknowledge if the costs in tables 1.4-8 and 1.4-9 include the cost <br />of topsoil salvaging and replacement for the K-Pit area, the Horse Gulch Fill and the K/G <br />Buttress Fill. If they do not, please revise the costs in tables 1.4-8 and 1.4-9 to reflect topsoil <br />salvaging and replacement in these areas. <br />9. A summary of estimated revegetation quantities and costs is associated with Table 1.4-10. This <br />table does not reflect the additional costs of revegetation associated with the K-Pit, Horse <br />Gulch Fill, and K/G Pit Buttress Fill. Please acknowledge if the costs in Table 1.4-10 include <br />the costs to revegetate the K-Pit, Horse Gulch Fill, and the K/G Buttress Fill, or revise the costs <br />to reflect the revegetation of these areas. <br />Additional Adequacy Comments <br />10. Section 4.09.1(10) requires that where the slope in the disposal area is steeper than 2.8h:1v (36 <br />percent), or such lesser slope as may be designated by the Division based on local conditions, <br />keyway cuts (excavations to stable bedrock) or rock toe buttresses shall be constructed to <br />stabilize the fill. Where the toe of the spoil rests on a downslope, stability analyses shall be <br />performed in accordance with Section 2.05.3(6)(b), (c) and (d) to determine the size of the rock <br />toe buttresses and keyway cuts. <br />The toe of the HG Fill does rest on a slight downslope, but the stability analysis has <br />demonstrated that a Factor of Safety greater than 1.5 can be achieved without the use of a <br />keyway or toe buttress. However, AAI has identified steeper portions of natural ground on the <br />northern sideslope of Horse Gulch, and states that benching is required for these areas (AAI <br />HG Fill Stability Analysis Figure 28). Based on the auger drilling data (Tables 1 and 2), these <br />slopes may be composed of thick, weak dark-brown clay. The application does not address the <br />proposed bench configurations and dimensions. <br />Please provide a description of the benching activities proposed for the steeper side slopes that <br />exist within the Horse Gulch Fill area.