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2022-09-29_PERMIT FILE - C1980007 (5)
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2022-09-29_PERMIT FILE - C1980007 (5)
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Last modified
10/6/2022 2:53:18 PM
Creation date
10/6/2022 2:51:53 PM
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Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
Permit File
Doc Date
9/29/2022
Doc Name
SUBSIDENCE EVALUATION
Section_Exhibit Name
Exhibit 60E Subsidence Evaluation for the South of Divide and Dry Fork Mining Areas
Media Type
D
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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 31 <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />coal face, and 3) the recompression of the caved material behind the support system. This system <br />therefore causes only a minimum amount of very low magnitude seismic activity (below the <br />threshold of feeling at the ground surface), particularly where the overburden depth to the coal <br />being mined is less than about 1,500 feet. <br />Based on field observations during the past 25 years, the major finding is that landslide movement <br />occurs in response to moisture and ground saturation and is not noticeably affected by subsidence <br />or any mine-related seismic activity caused by longwall mining beneath or near the landslides. <br />With regard to the landslide north of Minnesota Reservoir, longwall mining in the B-seam panel <br />B13-A did not have any observable effect on the landslide. The proposed E-seam mining in panel <br />E12 will occur further south and with shallower overburden. As shown in Map 1, the head of the <br />landslide will be located over the southern edge of panel E12, where subsidence is projected to be <br />between 4 and 4.5 feet. As a result, the upper portion will be subject to subsidence with the <br />outcome being a flattening of the slope in the upper reaches of the slide. This flattening of the <br />upper reaches of the slide will reduce the movement potential and likely focus any movement that <br />might occur to just the upper reaches. In addition, the overall slope of the mapped slide is less <br />than in adjacent areas, further suggesting greater stability and a reduced potential for reactivation. <br />Based on the above-mentioned historical evidence from the annual observations, the landslide <br />areas located north and south of Minnesota Reservoir are not expected to be impacted by mine- <br />induced subsidence and seismic activity when longwall Panels E16 and E17 is mined. Similar to <br />the landslide north of Minnesota Reservoir, any subsidence effect on the topography should be a <br />flattening of the slope, which would reduce movement potential. <br />Lastly, Mr. Dunrud has reviewed the conditions associated with the proposed mining activities and <br />the mapped landslide. It is his opinion that while subsidence might cause minor reactivation of <br />the landslide near the upper end, it is unlikely that there will be any movement that would reach <br />or effect Minnesota Reservoir. <br />10.2 Rockfalls <br />Rockfalls are the free-falling movement of rocks, which have become detached from cliffs or other <br />steep slopes, and move under the influence of gravity and the underlying ground surface. The <br />detached rocks roll and/or bounce downhill, depending on the slope (configuration of the ground <br />surface). Their movement continues until they are stopped by an obstruction or lose potential <br />energy and stop naturally. <br />A low to high potential exists for rockfalls in the Southern Panels and Sunset Trail mining areas. <br />Analysis of the terrain in these mining areas reveal slopes that range from 30 to 80 percent along <br />Minnesota Creek, the Dry Fork of Minnesota Creek and its tributaries, and in local areas along the <br />main fork of Lick Creek. Vertical displacement, tilt, and strain produced by mining may locally <br />trigger already unstable rocks to fall during, or shortly after mining. <br />The areas with steep slopes in the Southern Panels and Sunset Trail mining areas, which have the <br />greater potential for rockfalls, are located either in areas with local access roads, which have only <br />limited travel, or in areas remote from any access roads or other man-made features. Based on a
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