2009-06-09_PERMIT FILE - C1980007A (2)

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West Elk Mine The Box Canyon permit revision area encompasses the remainder of the Box Canyon lease tract. Only B Seam mining is planned in this area. Except as noted, the following discussion of mining, geology and subsidence impacts for the Box Canyon Mining area apply to Panel 25, in Sylvester Gulch. West Flatiron Mining Area -- This area is designated on Map IA and includes extensions of B-seam longwall panels 18A, 18, and 19. South of Divide Mining Area including the Dry Fork Lease - The mining area encompasses the E Seam longwall panels located primarily in Sections 32, 33, 34, 35 and 36 of Township 13 South, Range 90 West of the 6th Principal Meridian, and Sections 1, 2, 3, 4, and 5 of Township 14 South, Range 90 West of the 6th Principal Meridian. The panels are identified as E1 through E9. Dry Fork Lease in the South of Divide Permit Revision Area - The permit revision area is indicated by the regulatory boundary added to the mine permit, as shown on Map 1, and IA. Table 42 Definition of Subsidence Symbols Symbol Definition Dimensions S Vertical Displacement (Subsidence) L Sm Maximum Vertical Displacement (S,„==a•t) L S/Sm Ratio of Vertical Displacement to Maximum Vertical Displacement L/L Sh Horizontal Displacement L t Coal Extraction Thickness L a=(Sm/t) Subsidence Factor LA- a,,, Subsidence Factor above Chain Pillars L/L S = •t Maximum Subsidence Above Chain Pillars L d Overburden Depth L Sm/d Ratio of maximum vertical displacement to overburden depth L/L W, Critical Extraction Width' L/L W/d Mining Width to Overburden Depth Ratio L/L, M Tilt (Slope) L/L Mm Maximum Tilt L/L C Curvature, the reciprocal of Radius of Curvature rad/L (1/L) Cm Maximum Curvature rad/L (I/L) E Horizontal Strain (+) is Positive, (-) is Negative L/L Em Maximum Horizontal Strain L/L Angle of Drawl Degrees B Break Angle Degrees Angle of Major Influence Degrees r Radius of Major Influence L 1- Critical Extraction (Mining) Width - The width of a mining panel necessary for maximum subsidence to occur; the length of the panel must also be greater than, or equal to, critical panel width for maximum subsidence to occur. Critical width (W,,) commonly ranges from 1.0 to 1.4 times the overburden depth (d). Subcritical Mining Width - The width of a mining panel less than critical width (i.e., less than 1.0 to 1.4d). Supercritical Mining Width - The width of a mining panel greater than critical width. 2 - Angle of Draw - The angle-of-draw is the angle between a vertical line drawn upward to the ground surface from the edge of a mined panel (or section of panels) and a line drawn from the edge of a mined panel (or section of panels) to the point of zero surface subsidence (i.e. where there is no measurable or evident subsidence on the ground surface.) 2.05-105 Revised 06105, 03106, 04106 & 05106- PR10;11106- TR107; 09107& 02108-PR12; 04109- TR117