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The Ash Pit area overall pre-mining topography had slopes between 4 and 23 °, with the <br /> steeper slopes in the northern portion of the pit. Post-mining the slopes will range from 4 to 14' <br /> and will blend with the surrounding topography. <br /> The post-mining stability analysis for the Ash Pit showed that the AOC variance will significantly <br /> improve Safety Factors when compared to restoring the Ash Pit to AOC. <br /> Further, post-mining drainages will result in overall watershed improvements. For the Ash Pit, <br /> the drainage area for Johnson Gulch, which is the major drainage associated with the Ash Pit, <br /> will increase by approximately 3 acres. The pre- and post-mining drainage densities will change <br /> slightly, and the overall drainage gradient will decrease 1.5%. Sediment yield will decrease <br /> from 1.03 tons/acre to 0.56 tons/acre under the proposed post-mining configuration. <br /> Table 3.5-2 summarizes the pre- and post-mining characteristics for the Ash Pit. <br /> Table 3.5-2 Pre-and Post-Mining Characteristics for the Ash Pit <br /> Condition Acreage Slopes (°) Safety Drainage Gradient Sediment <br /> Factors Density N Yield <br /> (mi/m12) Per Acre <br /> (tons) <br /> Pre-Mining 1,432 4-23 1.36 3.1 9.3 1.03 <br /> Post-Mining 1,435 4-14 1.75 3.2 7.8 10.56 <br /> There would not be any significant changes in the post-mining watershed areas for the L Pit or the Ash <br /> Pit that would impact seasonal or flood flows from the post-mining reclaimed areas or adversely affect <br /> surrounding ecology or any existing or planned use of surface water or groundwater. <br /> Reclaiming to slopes that are not as steep as pre-mining slopes will improve the post-mining <br /> land use of rangeland by allowing for better cattle access and distribution of grazing. In <br /> steeper areas cattle typically congregate on less steep portions of slopes possibly resulting in <br /> over-utilization of these areas. Reducing the overall steepness of the reclaimed slopes will <br /> provide for more dispersed grazing and better resource utilization for post-mine land use. <br /> Landowners within the variance area have approved the proposed changes in post-mining <br /> topography. Landowner approval letters are included in Appendix B; Attachment 3. <br /> l--?,gvision, <br /> 3-43c ,Approved <br />