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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 39 <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <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.