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Subsidence Evaluation for the <br />Exhibit 60E South of Divide and Dry Fork Mining Areas Page 39 <br />13.0 POSSIBLE SUBSIDENCE CONSEQUENCES <br />Predicted subsidence impacts for the South of Divide and Dry Fork mining areas has been <br />described in detail above. The greatest surface impacts are expected to occur along the <br />precipitous slopes and cliffs that flank Minnesota Creek, Lick Creek, Deep Creek, and other <br />tributaries. Though unlikely, the worst possible consequences foreseen are that cracks could <br />locally form and be as much as 25 to 50 feet deep above chain pillars and barrier pillars in <br />bedrock on the precipitous slopes, ridges, and/or cliffs that flank Minnesota Creek, Lick Creek, <br />and other tributaries, and may locally accelerate the naturally- occurring rockfall and landslide <br />process. There is a portion of the Deep Creek Ditch that lies on bedrock and above projected <br />extended longwall panels E5 and E6 in the Dry Fork mining area. This should be monitored for <br />cracks and appropriate steps taken to mitigate them if they occur. <br />Some cracks are expected to occur on the Dry Fork access road in the area near the confluence of <br />Deer Creek and Dry Fork. Maximum vertical displacement ranging from 8.4 to 11.2 feet, tilt <br />from 1.3 to 6 percent, and horizontal strain from 0.7 to 4.2 percent are projected in the Dry Fork <br />valley above the western limits of longwall panels E2 and E3. <br />The extension of mining into the Dry Fork mining area is expected to minimally impact the <br />surface. The mining thickness is generally less (9 feet and 10 feet) than in the South of Divide <br />mining area and the minimum overburden is thicker (800 feet). The maximum vertical <br />displacement ranges from 6.0 to 8.0 feet, tilt from 0.7 to 2.3 percent and horizontal strain from <br />0.4 to 1.4 percent. Thus impacts should be minimal. <br />Based on subsidence observations by Dunrud (as discussed in Section 5.3.2), no cracks are <br />expected to occur in either the alluvium in the Dry Fork and Lick Creek drainages or stock <br />watering ponds and drainage diversion ditches. In addition, no cracks are predicted to occur in <br />colluvium more than about ten feet thick. The monitoring suggested in Section 11.3 will <br />compare results expected and actual field results. <br />�J <br />831 - 032.810 Wright Water Engineers, Inc. <br />mi <br />