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Subsidence Evaluation for the <br /> Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 39 <br /> 12.0 POSSIBLE SUBSIDENCE CONSEQUENCES <br /> Predicted subsidence impacts for the Southern Panels and Sunset Trail mining areas has been <br /> described in detail above. The greatest surface impacts are expected to occur along the precipitous <br /> slopes and cliffs that flank Minnesota Creek, Lick Creek, Deep Creek, and other tributaries. <br /> Though unlikely, the worst possible consequences foreseen are that cracks could locally form and <br /> be as much as 25 to 50 feet deep above chain pillars and barrier pillars in bedrock on the precipitous <br /> slopes,ridges, and/or cliffs that flank Minnesota Creek,Lick Creek, and other tributaries, and may <br /> locally accelerate the naturally-occurring rockfall and landslide process. <br /> E-seam mining in longwall panel E2 has already occurred underneath Dry Fork with mining <br /> thickness near 14 feet and with overburden as little as 375 to 400 feet. No adverse impacts to the <br /> Dry Fork stream channel or flow were observed during or subsequent to mining. Since this case <br /> represented the worst-case scenario, the stream channels in the Dry Fork watershed are not <br /> expected to be adversely impacted, even with two-seam mining. <br /> In the Sunset Trail mining area, conditions under the South Prong channel are expected to be <br /> similar to the Dry Fork channel in the South of Divide mining area. As noted in Section 5.3.2, <br /> reaches of South Prong underlain by bedrock are more susceptible to surface cracking. If this <br /> occurs away from the edge of the panel, then the crack will likely be short term and closed once <br /> the longwall mining progresses as discussed in Section 4.1. Surface cracks that persist are <br /> projected to be 5 to 15 feet deep and will not be hydraulically connected to the mine workings as <br /> discussed in Section 11.3.1 <br /> Based on subsidence observations by WWE(as discussed in Section 5.3.2),no cracks are expected <br /> to occur in either the alluvium in the Dry Fork, Lick Creek, and other tributaries or stock watering <br /> ponds and drainage diversion ditches. In addition, no cracks are predicted to occur in colluvium <br /> more than about ten feet thick. <br /> 831-032.912 Wright Water Engineers, Inc. <br /> December 2020 <br />