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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 42 <br />15.0 SUMMARY AND CONCLUSIONS <br />The measured subsidence parameters over the B -seam and E -seam longwall panels at the West <br />Elk Mine has fallen within the range of predicted subsidence parameters developed from the <br />original subsidence data collected over the Northwest B -seam longwall panels. In addition, the <br />annual subsidence field studies have observed subsidence effects at the expected locations and <br />consistent with the projections in the Exhibit 60 series. <br />The subsidence parameters also fall within the range of those measured and calculated by Dunrud <br />in four different coal mining areas in Colorado, Utah, and Wyoming (Dunrud 1987). The <br />subsidence parameters also are consistent with the appropriate National Coal Board graphs <br />(Figures 4 and 5). <br />Results of subsidence measurement and analysis in the West Elk subsidence monitoring area also <br />are in general agreement with the computer modeling programs developed in the Eastern United <br />States. These favorable comparative results calibrated by West Elk subsidence measurements, <br />therefore, give added assurance that the subsidence parameters projected for the Southern Panels, <br />Apache Rocks West, and Sunset Trail mining areas are realistic and correct. <br />Specific conclusions are as follows: <br />1. Maximum vertical displacement (subsidence), tilt, and horizontal strain predicted for the <br />Southern Panels, Apache Rocks West, and Sunset Trail mining areas are likely to be <br />conservative values. Subsidence monitoring data collected after mining of longwall panels <br />E 1 through E3 show that actual subsidence was at the lower end of the predicted range. <br />Similarly, the computer model projections overestimated the subsidence over panel E1, <br />while accurately predicting subsidence along Dry Fork over panels E2 and E3. <br />2. Mining of the longwall mining panels in the Southern Panels mining area will not impact <br />Minnesota Reservoir. The reservoir is completely out of the area of mining influence. All <br />mine workings, including E -seam and B -seam longwall panels are 500 to 600 feet farther <br />away from the reservoir footprint, using even a 45 -degree angle of draw. Mining in panels <br />E2 and E3 occurred without any adverse impacts to the reservoir. In addition, Minnesota <br />Reservoir is the outside area of influence for two -seam mining in the Apache Rocks West <br />mining area. <br />3. No cracks have been observed in the alluvium in any of the drainages of the Dry Fork of <br />Minnesota Creek, or Deep Creek. The composition and thickness of the alluvium in these <br />drainages make it unlikely for cracks to form in the stream channels of drainages in the <br />Southern Panels, Apache Rocks West, and Sunset Trail mining areas. Two -seam mining <br />under Dry Fork will produce some of the largest projected subsidence parameters <br />experienced at the West Elk Mine. However, based on the lack of adverse impacts due to <br />the E -seam mining, the B -seam panels B26 to B29 are not anticipated to impact the channel <br />due, in part, to the greater overburden thickness. <br />4. Mining impacts on rockfalls were not observed during annual subsidence observations in <br />the Apache Rocks and Box Canyon mining areas over six years (1999 to 2004 inclusive), <br />831-032.816 Wright Water Engineers, Inc. <br />October 2018 <br />