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West Elk Mhie <br />The Box Canyon permit revision area encompasses the remainder of the Box Canyon lease tract. Only <br />B Seam mining is planned in this area. Except as noted, the following discussion of mining, geology <br />and subsidence impacts for the Box Canyon Mining area apply to Panel 25, in Sylvester Gulch. <br />• <br />i? <br />West Flatiron Mining Area -- This area is designated on Map 1 A and includes extensions of longwall <br />panels 18A, 18, and 19. <br />South of Divide Mining Area including the Dry Fork Lease - The mining area encompasses the E <br />Seam longwall panels located primarily in Sections 32, 33, 34, 35 and 36 of Township 13 South, <br />Range 90 West of the 6 h Principal Meridian, and Sections 1, 2, 3, 4, and 5 of Township 14 South, <br />Range 90 West of the 6"' Principal Meridian. The panels are identified as E 1 through E9. <br />Dry Fork Lease in the South of Divide Permit Revision Area - The permit revision area is indicated <br />by the regulatory boundary added to the mine permit, as shown on Map 1, and IA. <br />Critical Mining Width - The width of a mining panel necessary for maximum subsidence to occur; <br />the length of the panel must also be greater than, or equal to, critical panel width for maximum <br />subsidence to occur. Critical width (Wcr) commonly ranges from 1.0 to 1.4 times the overburden <br />depth (d). <br />Subcritical Mining Width - The width of a mining panel less than critical width (i.e., less than 1.0 to <br />1.4d). <br />Supercritical Mining Width - The width of a mining panel greater than critical width. <br />Table 42 <br />Definition of Subsidence Terms <br />Symbol Definition Dimensions <br />S Vertical Displacement (Subsidence) L <br />Sm Maximum Vertical Displacement (S,- a•t) L <br />S/Sm Ratio of Vertical Displacement to Maximum Vertical <br />Displacement L/L <br />Sh Horizontal Displacement L <br />t Coal Extraction Thickness L <br />a=(Sm/t) Subsidence Factor L/L <br /> Subsidence Factor above Chain Pillars L/L <br />S, =a, •t Maximum Subsidence Above Chain Pillars L <br />d Overburden Depth L <br />Sm/d Ratio of maximum vertical displacement to overburden depth L/L <br />W, Critical Extraction Width L/L <br />W/d 1? lining Width to Overburden Depth Ratio L./L <br />M Tilt 1 Slo el LL <br />Mm Maximum Tiit L/L <br />C Curvature. the reciprocal of Radius of Curvature rad/L (l/L) <br />Cm Ma-Ni nt:m Curvature rad/L (I /L) <br />E Horizontal Strain (+) is Positive(-) is N- Te anve L/L <br />Em j Itiia?:imum Horizontal Strain UL <br /> Angle of Draw Degrees <br />B Break Angle Degrees <br /> Angel of Major Influence Degrees <br />r Radius of Major Influence L <br />2.05-105 Revised June 200.1 PR 10, Rev. Harch 2006; Rev. April 2006 PR10; May 2006 PRI G, A'ov. 2006 TR107, Sep. 2007 PR-1?;Feb. 2008PR-12