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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 precipitous <br />slopes and cliffs that flank Minnesota Creek, Lick Creek, Deep Creek, and other tributaries. Though <br />unlikely, the worst possible consequences foreseen are that cracks could locally form and be as <br />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. There is a small portion of <br />the Deep Creek Ditch that lies on bedrock and above the chain pillars of panel E5 in the Dry Fork <br />mining area. This should be monitored for cracks and appropriate steps taken to seal them if they <br />occur. <br />Some cracks are expected occur on the Dry Fork access road, however, in the area near the <br />confluence of Deer Creek and Dry Fork. Maximum vertical displacement ranging from 8.4 to 11.2 <br />feet, tilt from 1.3 to 6 percent, and horizontal strain from 0.7 to 4.2 percent are projected in the Dry <br />Fork 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 surface. <br />The mining thickness is generally less (9 feet and 10 feet) than in the South of Divide mining area <br />and the minimum overburden is thicker (800 feet). The maximum vertical displacement ranges <br />from 6.2 to 7.0 feet, tilt from 1.0 to 1.9 percent and horizontal strain from 0.6 to 1.0 percent. Thus <br />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 watering <br />i ponds and drainage diversion ditches. In addition, no cracks are predicted to occur in colluvium <br />more than about ten feet thick. The monitoring suggested in Section 11.3 will compare results <br />expected and actual field results. <br /> <br />Tetra Tech - 0907171P 3