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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 resulting from the modeling completed in the Exhibit 60 series. <br /> The subsidence parameters also fall within the range of those measured and calculated by Dumud <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 measurements and analyses 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 <br /> longwall mining in the Southern Panels, Apache Rocks West, and Sunset Trail mining <br /> areas are likely to be conservative values. Subsidence monitoring data collected after <br /> mining of longwall panels E1 through E3 show that actual subsidence was at the lower end <br /> of the predicted range. Similarly, the computer model projections overestimated the <br /> subsidence over panel E1, while accurately predicting subsidence along Dry Fork over <br /> 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 /> 831-032.912 Wright Water Engineers, Inc. <br /> December 2020 <br />