2011-02-14_PERMIT FILE - C1980007A (3)

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Subsidence Evaluation for the Exhibit 60E South of Divide and Dry Fork Mining Areas Page 46 • well monitoring continue to be conducted before, during, and after mining in order to determine any mining effects. 8. Although no cracks are expected in the soft, pliable alluvium of the Dry Fork, some cracks are expected to occur on the harder and more highly compacted Dry Fork access road, particularly in the area near the confluence of Deer Creek and Dry Fork. As discussed previously, the range of maximum vertical displacement, tilt, and horizontal strain is projected to be 8.4 to 11.2 feet, 1.3 to 6.4 percent, and 0.7 to 4.2 percent (respectively) in the Dry Fork stream valley and road above the solid coal boundaries at western limits of E -seam longwall panels E2 and E3. 9. The extension of mining into the Dry Fork mining area is expected to minimally impact the surface. The mining thickness is generally less (9 feet and 10 feet) than in the South of Divide mining area and the minimum overburden is thicker (800 feet). The maximum vertical displacement ranges from 6.0 to 8.0 feet, tilt from 0.7 to 2.3 percent, and horizontal strain from 0.4 to 1.4 percent. Thus impacts should be minimal. 10. There is a portion of the Deep Creek Ditch that lies on bedrock and above E -seam longwall panels E5 and E6 if extended east in the Dry Fork mining area. It is recommended that this area be monitored for cracks and appropriate steps taken to seal them, if they occur. 11. Subsidence effects on buildings have not been observed in the Apache Rocks and Box . Canyon mining areas. Baseline information on buildings, such as foundations, walls, chimneys, and roofs, has already been obtained prior to any mining on the Dry Fork Cow Camp in July 2004 (Dunrud 2004b). A pre - mining survey of the Cow Camp structures was performed by West Elk Land Surveying in February 2006. The Minnesota Creek ditch rider's cabin is located near the headwaters of Dry Fork in the Dry Fork mining area. An exterior inspection of the cabin was performed in 2004 by the U.S. Forest Service and Agapito Associates, Inc. ( Agapito, 2005). The structure was reported to be in average structural condition. A pre - mining survey of this structure is recommended. As the longwall mining face moves westward within the area of mining influence of the Cow Camp cabin, a subsidence wave — moving at about the same rate as the mining face — will pass beneath the cabin, subjecting it to (1) tilt and strain, (2) then maximum vertical displacement, (3) then relaxation of these effects, as the longwall mining face moves out of the area of mining influence. The cabin, though temporarily tilted until the longwall face moves out of the area of influence of the cabin, is expected to remain intact during the subsidence episode, because it is small and light, and of wood construction. However, cracks are expected to occur in the foundation, in response to the tilt and strain caused by the subsidence wave produced by the moving longwall mining face below. The Minnesota Creek Ditch Rider's cabin is located above E -seam longwall panel E6 if extended further east than currently planned and is expected to experience similar effects as those described above for the Cow Camp cabin. 831 - 032.810 Wright Water Engineers, Inc.