2010-03-04_REVISION - C1996083 (3)

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C-1996-083 TR-65 MLT Adequacy Review 04-Mar-2010 Page 2 of 3 for the vicinity of the West Mains, in a manner consistent with monuments established elsewhere at the mine. No response required. MTI 2004 Section 3.0 - Geotechnical Framework 16. Section 3.1 describes the geologic setting of the Somerset Coal Field and the Bowie No. 2 Mine. The "West Mains fault" is addressed at the bottom of Page 9, but does not appear on Figure 1 of Maleki. A faint, dashed line does appear on revised Map 27 (and on PAP Map 07 - Geology) in the approximate location described by MTI 2004. Map 08 (Geologic Cross Section) of the PAP clearly illustrates the interpreted magnitude of the fault, and implies a near-vertical plane. Due to the potential significance of this feature, its existence should be clearly indicated on each Map for which the fault may be pertinent. At a minimum, please modify Maps 07, 14-B and 27 to clearly portray the location of what the Division understands to be the "West Mains fault ". For Map 07, it may be more accurate to illustrate the location on the surface, if known, rather than at the B- or D-seam depth. The West Mains fault has been added to Maps 07 and 27. Please add the predicted fault trace to Map 14-B, as originally requested. MTI 2004 Section 4.0 - Mains Orientation and Pillar Designs 17. The stability of near-seam strata was evaluated at the corridor for the layout illustrated in MTI 2004 Figure 1. An empirical technique developed by NIOSH was used to confirm that the (then-planned) orientation was optimal for stability of the rooms with respect to the horizontal stress field. As stated in 4.1 - Mains Orientation, "the rule of thumb is that the mains should be oriented near parallel to maximum horizontal stress to minimize roof stability problems." The orientation of the mains evaluated for MTI 2004 was N 100° E, which was deemed to be favorable because it lay within 20 degrees of the maximum stress orientation (N 90° E). However, the orientation of the mains illustrated on revised Maps 14-B and 27 appears to be N 55° E, which is skewed 35 degrees from the maximum stress orientation. The bearing of the West Mains corridor has been rotated 45 degrees from the layout evaluated in 2004. Please re- evaluate the stability of near-seam strata using the corridor layout now proposed with TR-65. MTI 2010 does not specifically evaluate the stability of near-seam strata using the corridor location proposed with TR-65, but pillar stresses and factors of safety were analyzed (see item 18). No additional response to this item is required.