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 36 11.6 Buildings 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 on the Dry Fork Cow Camp in July 2004 (Dunrud 2004b) prior to any mining. A pre - mining survey of the Cow Camp structures was performed by West Elk Land Surveying in February 2006 and is included as Exhibit 73. 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. It is recommended that a pre- mining survey be conducted for this structure. 11. 6.1 Lower Dry Fork Cow Camp The cabin exterior is approximately 13 feet wide, 20 feet long, and 8.5 feet high (the wall height). A lean-to 7 feet long and a porch 5.5 feet wide are located on the north and south ends of the cabin (see Figures 7 and 8, of Exhibit 60D for details). The outside walls are of a wood, board -and -bat construction. The foundation, which is of rock and mortar construction (and an estimated 1% feet thick), ranges from about 1 foot high in the back to 20 inches high in the front. The roof is covered with tin. The side windows, which measure 2 by 3 feet in outside dimension, are located in the . approximate center of either wall. Estimated maximum ranges of vertical displacement (S.), tilt (M.), and horizontal tensile and compressive strain (E,„ and –E,„) in the cow camp cabin area are as follows, assuming 14 ft of coal is extracted (see Table 2, Exhibit 60B): S =9 -loft; M =2 -5 %; E m ,- E 0.8 -3 %. As the longwall mining face moves westward within the area of mining influence of the 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. Although the cabin, is projected to be temporarily tilted as it is undermined, it is expected to remain intact during the subsidence episode, because it is small and light, and of wood construction. However, cracks could 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 cracks, which may reach a maximum temporary width of a fraction of an inch to perhaps 1 to perhaps 1'/, inches, will likely close again when the longwall mining face moves out of the area of mining influence of the cabin. Any cracks that develop in the foundation, however, may continue to be visible for the life of the foundation. • 831 - 032.810 Wright Water Engineers, Inc.