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0 <br />• 4. Contour mining and,=.backfill is planned in lower Lorencito Canyon. Small <br />excess spoil fills a5edimentation ponds are associated with the <br />contour mining. ` <br />Area Mining <br />The extent of surtace area mining is shown on Fig. 1. Post mining contours are <br />planned to reflect approximate original contours. The steepness of existing slopes is <br />characterized on Fig. 2. Slope heights range from about 200 to 250 feet. Area slopes <br />outside of excess spoil fills are mostly flatter than 3:1 (horizontal:vertical). The <br />maximum fill slope recommended is about 2:5:1. Erosion control and constructability <br />concerns could result in desired slope angles of about 3:1. Where existing slopes are <br />steeper than 2.5:1, post-mining slopes will need to be flatter. A variance may be <br />required. Design of post-mining topography will need to address this issue. <br />Excess Disposal Fills 4 through 9 <br />~ To characterize the spoil fills we estimated elevation and slope information as <br />shown on Fig. 1. Typical plan and section views are shown on Fig's. 3 and 4. The fill <br />heights range from about 50 feet to 250 feet (toe to crest) with the maximum thickness <br />of fill ranging from about 50 to 170 feet. The proposed geometry of the fill slopes is a <br />2.5:1 {horizontal:vertical) slope face, with 20-foot wide benches at 40-foot vertical <br />intervals. This results in an overall slope on the order of 3:1. <br />We estimated the average valley slope, maximum side slopes and volume to <br />compare to the Colorado Division of Minerals and Geology (CDMG) definition of Valley <br />Fills. For classification purposes, the area outside the extent of surface mining (shown <br />on Fig. 4) was used. For stability analysis the full height slope was used. A Valley Fill <br />is subject to specific underdrain size requirements and is defined by CDMG regulations <br />as "a fill structure consisting of any material other than coal waste and organic material <br />LORENCITO COAL COMPANY, LLC <br />LORENCITO SURFACE MINE • PHASE I <br />CTLR 32, 611 3 <br />