2008-03-21_PERMIT FILE - C1980007A (5)

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West Elk Mine • 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 Pen-nit 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 in- cluding Dry Fork muting area (60E), as the primary future mining area, but retain discussion' of subsidence parameters for the Apache Rocks, Box Canyon,, and West Flatiron 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 areas. Specifically, MCC has retained Wright Water Engineers, Inc. (WWE) of Denver to evaluate subsidence and probable hydrologic consequences. WWE worked closely with Mr. C. Richard 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 particular note with respect to this South of Divide permit revision document, is the report prepared by Mr. Dunrud entitled, Some Engineering Factors Controlling Coal Mine Subsidence in Utah and Colorado (Dunrud 1976). In that report, Mr. Dunrud evaluated subsidence in the Mesaverde Formation at the Somerset Mine, less than two miles from the West Elk Mine. Working closely with Mr. Dunrud, WWE has adopted the following multi-faceted approach to quantifying subsidence in the permit area: I . The existing longwall panels at the mine site have been extensively monitored and WINE has • evaluated the relevant data. These data provide the basis for Mr. Dunrud's conceptual model, which is described later in this permit text and in Exhibits 60 and 60B. Please note that Exhibit 60 addresses the Apache Rocks and Box Canyon mining areas and Exhibit 60B specifically addresses the South of Divide mining area. (Exhibit 60C addresses the subsidence and geologic hazards for the West Flatiron lease tract). Exhibit 60D addresses Geologic Hazard Field Observations for the South of Divide Mining Area. Exhibit 60E, completed by TetraTech, Inc., addresses the extensions of Panel E1 through E 6 into the Dry Fork Lease. 2. WWE has utilized a computer model to quantify subsidence, and this thodel has been calibrated using the data collected at West Elk Mine. The model was developed by Dr. Syd Peng and Dr. Yi Luo at West Virginia University and is referred to as the "Comprehensive and Integrated Subsidence Predict'i'on Model (CISPM)." 3. WWE has thoroughly reviewed the literature regarding subsidence and associated hydrologic consequences. We have checked the findings associated with Ndr. Du u-ud's conceptual model and the CISPM innodel with findings from case studies as described in the literature, and we have concluded that the results are consistent. 4. Finally, subsidence projections described herein have been carenzily reviewed by Mr. Dunrud for reasonableness. IvIr. Dunn_-ud has visited the West Elk Mine a_ea on _n==Iny occasions and he is familiar with key factors pertaining to subsidence as they relate to the South of Divide and other active mining areas. Consequently, Mr. Dunrud is v.,ell qualified to draw conclusions about the nature of subsidence that is likely to occur. 2.05-106 Reused June 3005 PRIO. Reis. Harch 2006: Rev. Apri1 ?006 PRIO; hlay?006 PRIO, Nov. 2006 TRI07 Sep. 2007 PR-1?; Feb. 2008PR-12