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3-43c <br /> <br />The Ash Pit area overall pre-mining topography had slopes between 4 and 23 °, with the steeper <br />slopes in the northern portion of the pit. Post-mining the slopes will range from 4 to 14° and <br />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 <br />Factors <br />Drainage <br />Density <br />(mi/mi2) <br />Gradient <br />(%) <br />Sediment <br />Yield <br />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 0.56 <br /> <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.