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• • Eastern Panels -The eastern panels, which trend about N80°W, will range from about <br />critical to subcritical in width in the west ends of panels 1, 2, 3, and 4 SE (numbered from <br />north to south) to subcritical in the eastern part of the panels: Maximum subsidence (Sm a t) <br />above panel centers is projected to range from 4.8 to 6 feet (0.4t to O.St) beneath areas of <br />greatest overburden depth to 7.2 to 9.6 feet (0.6t to 0.8t) near the head of Sylvester Gulch. <br />The maximum subsidence above the chain pillars (SAP ant) is projected to range from 2.4 <br />feet (0.2t) in areas of thinnest overburden to 6.0 feet (O.St) feet in areas of thickest <br />overburden. <br />The Marine Sandstone located beneath the D-Seam is about 100 feet thick in the eastern panel <br />area. This sandstone may reduce the subsidence factor, compazed to the western panel area, <br />where the sandstone is less than 50 feet thick. <br />• Western Panels E-Seam Mining -For E-Seam mining, all 'three western panels (numbered <br />from south to north) will be of supercritical width (i.e., mining width greater than critical; <br />critical width is the mining width needed to cause maximum subsidence) in areas near the <br />head of Pond Gulch, in the Horse Gulch area, and the two unnamed draws east of Horse <br />Gulch. Only in azeas of the higher ridges adjacent to these draws will the panels be of <br />subcritical width (mining width less than critical). With a projected longwall panel width of <br />950 feet, assuming an 11-foot coal-extraction thickness and chain pillaz dimensions and <br />geometry similaz to the current West Elk mining area, maximum subsidence is projected to <br />range from 6.6 to 8.8 feet (0.6t to 0.8t). <br />• Maximum subsidence is expected to be closer to 6.6 feet (0.6t)~ beneath the ridges and closer to <br />8.8 feet (0.8t) beneath the draws. Maximum subsidence above the chain pillars (S~) is <br />predicted to range from 0.6 feet (O.OSt) where the overburden is thinnest (in the draws) to about <br />3.6 feet (0.3t) beneath the ridge azeas. Maximum subsidence may be less in the northeastern <br />part of the panel area where the Marine Sandstone beneath the D-Seam is about 100 feet thick. <br />Western Panels-Combined E and B-Seam Mining -For E-Seam mining and subsequent B- <br />Seam mining, the three mining panels will range from supercritical to critical in the draw <br />azeas, previously mentioned in the E-Seam mhung section; to subcritical in the ridge azeas <br />adjacent to these draws. Because the total extraction thickness will average 23 feet (E- <br />Seam, 11 feet; B-Seam, 12 feet), the total maximum subsidence (vertical displacement) after <br />mining both seams is projected to range from about 13.8 to 48.4 feet (-0.6t to 0.8t). ' <br />Box Canyon Mining area -Overburden depth above the projected longwall panel centers in <br />the Box Canyon mining area (in the B-Seam) ranges from about 750 feet beneath Box <br />Canyon and the unnamed gulch west of Box Canyon toy about 2,300 feet beneath West <br />Flatiron (see Map 14 for details). With a projected longwall panel width of 1,100 feet, <br />assuming acoal-extraction thickness of 12 feet and chains pillar dimensions similar to the <br />current West Elk mining azea, maximum subsidence (Sm at) is projected as follows: <br />1. The first two northern panels will range from supercritical to critical at points of minimum <br />• overburden depth beneath the canyons to subcritical beneath ridges on the flanks of West <br />2.05-]]6 <br />March 2005PR1/ <br />,,, ~yA7 <br />