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West Elk Mine <br />to south) to subcritical in the eastern part of the panels. Maximum subsidence (Sm=a t) above <br />panel centers is projected to range from 4.8 to 6 feet (0.4t to O.St) beneath areas of greatest <br />overburden depth to 7.2 to 9.6 feet (0.6t to 0.8t) neaz the head of Sylvester Gulch. The <br />maximum subsidence above the chain pillars (S~ ae~t) is projected to range from 2.4 feet (0.2t) <br />in areas of thinnest overburden to 6.0 feet (O.St) feet in areas of thickest 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, compared to the western panel area, <br />where the sandstone is less than 50 feet thick. <br />• Western Panels E Seam Mininz - For E Seam mining, all throe western panels (numbered from <br />south to north) will be of supercritical width (i.e., mining width greater than critical; critical <br />width is the mining width needed to cause maximum subsidence) in areas neaz the head of Pond <br />Gulch, in the Horse Gulch azea, and the two unnamed draws east of Horse Gulch. Only in areas <br />of the higher ridges adjacent to these draws will the panels be of subcritical width (mining width <br />less than cridcal). With a projected longwall panel width of 950 feet, assuming an 11-foot coal- <br />extraction thickness and chain pillaz dimensions and geometry similaz to the current West Elk <br />mining azea, maximum subsidence is projected to 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 azea where the Marine Sandstone beneath the D-Seam is about 100 feet thick. <br />For E Seam mining and subsequent B Seam mining, the three mining panels will range from <br />supereriticai to critical in the draw areas, previously mentioned in the E Seam mining section, to <br />subcritical in the ridge azeas adjacent to these draws. Because the total extraction thickness will <br />average 23 feet (E Seam, 11 feet; B Seam, 12 feet), the total maximum subsidence (vertical <br />displacement) after mining both seams is projected to range from about 13.8 to 18.4 feet (-0.6t <br />to 0.8t). <br />Box Carryon Mining Area -Overburden depth above the projected longwall panel centers in the <br />Box Canyon mirring azea (in the B Seam) ranges from about 750 feet beneath Box Canyon and the <br />unnamed gulch west of Box Canyon to about 2,300 feet beneath West Flatiron (see Map 14 for <br />details). With a projected longwall panel width of 1,100 feet, assuming acoal-extraction thickness <br />of 12 feet and chain pillar dimensions similar to the current West Elk mining area, maximum <br />subsidence (Sm aY) 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 />Flatiron. Maximum subsidence (Sm) above panel centers is projected to range from 7.2 to 9.6 <br />feet (0.6t to 0.8t) beneath the canyons to about 6.0 to 8.4 feet (O.St to 0.7t) beneath areas of <br />greatest overburden depth. Maximum subsidence above chain pillars (S~) is projected to range <br />from 1.2 to 3.6 feet (O.lt to 0.3t). <br />2.05-114 Revised November 1004 PRIO <br />