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West Elk Mine 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. • Table 42 Definition of Subsidence Tenns S mbol Definition Dimensions S Vertical Displacement (Subsidence) L Sm Maximum Vertical Dis lacement Sm=a t L S/Sm Ratio of Vertical Displacement to Maximum Vertical Dis lacement LIL Sn Horizontal Dis lacement L t Coal Extraction Thickness L a= S„Jt Subsidence Factor UL a Subsidence Factor above Chain Pillars UL S =a •t Maximum Subsidence Above Chain Pillars L d Overburden De th L Sm/d Ratio of maximum vertical displacement to overburden de th UL WQ Cdtical EMradion Width UL W/d Minin Width to Overburden De th Ratio UL M Tilt Sloe UL Mm Maximum Tilt UL C Curvature the red rocel of Ratlius of Curvature rad/L 1/L Cm Maximum Curvature rad/L 1/L E Horizontal Strain (+) is Positive, (-) is Negative LIL Em Maximum Horizontal Strain UL ~ Angle of Draw Degrees B Break An le De Tees An el of Ma'or Influence De rees r Radius of Ma'or Influence L The focus of Exhibit 60B is on the South of Divide Mining Area. It is not feasible to quantify subsidence by reference strictly to the Permit Revision Area; to the contrary, it is necessary to evaluate the relevant panels in their entirety. Exhibit 60 addresses subsidence in the Apache Rocks and Box Canyon mining areas. Since mining activities are continuing in these areas, Exhibit 60 has been retained in the permit. The discussions in this section, however, focus on the South of Divide mining area, as the primary future mining area, but retain discussion of subsidence parameters for the Apache Rocks and Box Canyon mining areas. MCC has made a major commitment to thoroughly understanding and describing the nature of subsidence that will occur in the South of Divide and other active mining azeas. Specifically, MCC has retained Wright Water Engineers, Inc. (WWE) of Denver to evaluate subsidence and probable hydrologic consequences. WWE worked closely with Mr. C. Richazd Dunrud on this project. Mr. Dunrud was employed by the U.S. Geological Survey (USGS) throughout his career and is a recognized authority on subsidence. Of particulaz note with respect to this South of Divide pernut revision document, is the report prepared by Mr. Dunrud entitled, Some Engineering Factors Controlling Coal Mine Subsidence in Utah and Colorado (Dunrud 1976). hi that report, Mr. 1.05-94 Revised November 2004 PRIO