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1 Sanborn Creek Subsidence Page 5 September 2, 1997 <br />' MINING ENVIRONMENT <br />' The planned location of the thirteen B Seam longwall panels is <br />shown on Figure 1. Five depth contours are shown; 2500-f t, <br />J 2000-ft, 1500-ft, 1000-ft and 500-ft. Longwall mining will proceed <br />_' from the maximum depth of Panels #2 - #13 toward the shallower <br />existing Sanborn Creek Mine workings. The long axis of Panel #1 <br />-- will roughly parallel to the strike of the B Seam and increases <br />1 erratically in depth by about 260-ft from east to west because of <br />the ridges that protrude into the North Fork valley between Bardine <br />_ Canyon and "C" Gulch. <br />'' The drill hole interburden lithology data provided was broken <br />down into the proportions of sandstone, shale and coal and is <br />presented in Table 1, The lithologic distribution in the <br />-' interburden is variable. However, sandstone is the predominant <br />lithology present in the interburden. Sandstone is the most <br />- favorable lithology for multiple seam mining, which is the case for <br />1 portions of all of the planned Sanborn Creek Mine longwall panels. <br />Sandstone is favorable because of its generally higher strength <br />-' which more rapidly distributes the stress concentrated under the <br />barrier pillars in the overlying mine workings (Chanda, 1989). <br />-- Figure 2 indicates that the weighted average 56$ sandstone <br />' recorded in the borehole logs (Table 1) actually predicts an 18° <br />angle of draw. The use of a 25° angle of draw conservatively <br />- extends the predicted area of longwall mining induced subsidence <br />effects to a greater distance beyond the surface projection of the <br />-' mining boundaries, approximately 99~ greater, than predicted by the <br />l 18° lithology based angle of draw. <br />-' The geometric conditions of each of the planned Sanborn Creek <br />Mine longwall panels are presented in Table 2. Specifically, the <br />-'~ individual planned longwall panel dimensions and the approximate <br />.' depth of various locations along the boundaries of the panel, i.e. <br />the depth at the center of the starter room, where the panel <br />ribsides are one-half the panel width from the ends of the panel, <br />1 where the depth contours cross the panel boundaries and the depth <br />at the center of the face-support recovery room. Table 2 <br />-- demonstrates that the maximum depth of the individual panels is at <br />the starter room and, except for Panel #1, the minimum depth at the <br />face-support recovery room. The southeast corner of Panel #7 is <br />approximately 90-ft lower than the center of the recovery room <br />because of the side-hill slope on the west side of Hawksnest Creek. <br />Lt Similarly, the west end of the Panel #10 recovery room is slightly <br />shallower than the center and the east end of the Panel #11 <br />recovery room is slightly shallower than the center because of the <br />~~ side-hill slopes of "A" Gulch. <br />1 <br />-' S <br />