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11.6 Buildings <br />Subsidence effects on buildings have not been observed in the Apache Rocks and Box Canyon <br />mining areas. Baseline information on buildings, such as foundations, walls, chimneys, and roofs, <br />has already been obtained prior to any mining on the Dry Fork Cow Camp in July 2004 (Dunrud <br />2004b). A pre-mining survey of the Cow Camp structures was performed by West Elk Land <br />Surveying in February 2006 and is included as Exhibit 73. The Minnesota Creek ditch rider's cabin <br />is located near the headwaters of Dry Fork in the Dry Fork mining area. An exterior inspection of the <br />cabin was performed in 2004 by the U.S. Forest Service and Agapito Associates, Inc. (Agapito, <br />2005). The structure was reported to be in average structural condition. A pre-mining survey should <br />be conducted for this structure. <br />11.6.1 Lower Dry Fork Cow Camp <br />The cabin exterior is approximately 13 feet wide, 20 feet long, and 8.5 feet high (the wall height). A <br />lean-to 7 feet long and a porch 5.5 feet wide are located on the north and south ends of the cabin <br />(see Figures 7 and 8, of Exhibit 60D for details). The outside walls are of a wood, board-and-bat <br />construction. <br />The foundation, which is of rock and mortar construction (and an estimated 1'/2 feet thick), ranges <br />from about 1 foot high in the back to 20 inches high in the front. The roof is covered with tin. The <br />side windows, which measure 2 by 3 feet in outside dimension, are located in the approximate <br />center of either wall. <br />Estimated maximum ranges of vertical displacement (Sm), tilt (Mm), and horizontal tensile and <br />compressive strain (Em and -Em) in the cow camp cabin area are as follows, assuming 14 ft of coal <br />is extracted (see Table 2, Exhibit 60B): <br />Sm = 9 -10 ft; Mm = 2 - 5%; Em, -Em = 0.8 - 3%. <br />As the longwall mining face moves westward within the area of mining influence of the cabin, a <br />subsidence wave-moving at about the same rate as the mining face- will pass beneath the cabin, <br />subjecting it to (1) tilt and strain, (2) then maximum vertical displacement, (3) then relaxation of <br />these effects, as the longwall mining face moves out of the area of mining influence. <br />The cabin, though temporarily tilted until the longwall face moves out of the area of influence of the <br />cabin, is expected to remain intact during the subsidence episode, because it is small and light, and <br />of wood construction. However, cracks are expected to occur in the foundation, in response to the <br />tilt and strain caused by the subsidence wave produced by the moving longwall mining face below. <br />The cracks, which may reach a maximum temporary width of a fraction of an inch to perhaps 1 to <br />perhaps 1 %4 inches, will likely close again when the longwall mining face moves out of the area of <br />mining influence of the cabin. Any cracks that develop in the foundation, however, may continue to <br />be visible for the life of the foundation. <br />Cracks, of as much as 1 to perhaps 1 %4 inches wide, are also expected to locally occur in the Dry <br />Fork road near the Cow Camp and elsewhere during mining. The cracks will likely close again once <br />the longwall mining face moves out of the area of influence of the road area. <br />11.6.2 Minnesota Creek Ditch Rider's Cabin <br />This cabin was built in the 1950's and is 24 feet 4 inches by 16 feet 4 inches single-story wood <br />framed building. The cabin is located outside of the angle of draw for the planned mining and thus <br />no impacts from mining are expected. It is recommended that a pre-mining survey of the structure <br />be performed. <br />Tetra Tech - 0907171P 29