2011-02-02_REVISION - C1980007 (2)

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MCOAL NYL.L.C. A Subsk lmy of Arch Weste n L3Ihm Woos Grasp, LLC February 02, 2011 Mr. Tom Kaldenbach Colorado Division of Reclamation, Mining and Safety Office of Mined Land Reclamation 1313 Sherman Street, Room 215 Denver, Colorado 80203 West Elk Mine P.O. Box 591 5174 Highway 133 Somerset, CO 81434 (970) 929.2200 Fax (970) 929-5050 Re: Mountain Coal Company, LLC, West Elk Mine; Permit No. C-1980-007; Technical Revision No. TR-124, Addition of Maximum Projected Areal Extent of Potential Mining; Responses to Adequacy Comments Dear Mr. Kaldenbach: Mountain Coal Company, LLC (MCC) provides the following responses to the adequacy comments on Technical Revision No. 124 per your letter of February 01, 2011. The Division's comments are quoted below and are followed by MCC's responses. 10. "Please revise Map 51 to show a 20-degree angle of draw around the perimeter of the workings. Please use the method of determining vertical distance that is explained in our letter of January 27, 2011 regarding Appendix B of MCC's Spring 2010 subsidence report. A 20-degree angle of draw is appropriate based on the 18.4-degree value at Station 101 of the Appendix, plus an assumed additional amount of 10% to recognize the maximum angle of draw at a location may be greater than 18.4 degrees. Also, please change the wording in the Map 51 legend that begins with "Approximate limit of the maximum" to the following: Subsidence boundary at 200 angle of draw using the greatest vertical distance in each projected mining area (vertical distance is the elevation difference between the projected edge of the subsidence basin on the land surface and the nearest edge of the longwall panel)." In compliance with Rule 2.05.6(6)(e)((F)(III), MCC will revise Map 51 to show "the ground surface areal extent of an area determined by the projection of the angle of draw, if predicted ... or 45', if no prediction...", at the revised predicted maximum E- seam angle of draw of 190. This maximum predicted value was provided in the revised Spring Subsidence Report Appendix B memorandum by Wright Water Engineers (WWE) also submitted to the Division today. While it can be argued that the angle of draw at a future location could be larger than 18.4° that was measured at Station 101, we are not aware of any evidence that this is the case and do not believe this single measurement justifies an extra 10% to be added. As presented in the revised Appendix B memorandum, the predicted angle of draw for the E-seam in Exhibit 60E currently ranges from 15° to 17° and was based on the subsidence monitoring data from MCC's B-seam longwall mining. The E- seam subsidence data predominantly conforms to the predicted range with one exception (Station 101) at 18.4°. All other data from the B-seam and E-seam show angles of draw less than the maximum predicted value of 17°. Nonetheless, MCC agrees with WWE's recommendation that the maximum predicted E-seam angle of