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October 11, 2011 <br />2.0 BACKGROUND INFORMATION <br />Page 2 <br />The renewable resource lands existing in the form of the Purgatoire River and associated <br />alluvial valley floor are unlikely to be impacted by the anticipated subsidence in this mining <br />plan. The renewable resources are shown on Map 20. The descriptions of the renewable <br />resource lands are available in Exhibit 8. The current mining plan (TR58 —Map 3) under the <br />Purgatoire River and associated alluvial valley floor are development -only workings and do not <br />have any retreat panels. All Maps and Exhibits referenced in this report may be found in the <br />New Elk permit document C 1981012. <br />The stability of development -only workings was analyzed using the Analysis of Retreat <br />Pillar Mining Stability ( ARMPS) computer code developed by the National Institute for <br />Occupational Safety and Health (NIOSH). The program uses the modified Mark - Bieniawski <br />pillar stability formulas and evaluates the stability within a zone comprising a number of pillars. <br />Development -only pillar dimensions were developed for areas underneath the renewable <br />resource lands mentioned above, and areas with cover depth and mining height combinations that <br />preclude the use of retreat mining. <br />For retreat mining, the ARMPS analysis was performed assuming a front gob of one -half <br />the panel length and a single -side gob of a mined -out panel. With ten 20 -ft -wide entries and <br />90 -ft square pillars (center -to- center), the stability factor (SF) for this case was 2.69 for mining <br />5 -ft -thick coal at a depth of 600 ft. This geometry results in an extraction of 39.5% before pillar <br />recovery. The SF of the 90 -ft -wide barrier pillar between the adjacent mined -out panel and the <br />active panel was estimated at 3.8, which will be mined during retreat. Stable retreat panel pillar <br />dimensions (with a SF of at least 1.5 for active panels) were developed for various cover depth <br />and mining height combinations using ARMPS, which will be utilized to develop pillar sizes <br />under variable cover depths and mining heights. <br />Research of the National Register of Historic Places indicates that there are no historic <br />places near New Elk which will be affected by the mine's operation. The mining area underlies <br />the Bosque del Oso State Wildlife area which was transferred to the state by previous mine <br />owners. New Elk has the right to mine in this area as governed by a lease agreement. No <br />surface mining is currently taking place in the vicinity of the New Elk Mine. To New Elk's <br />knowledge, no surface mines are planned in the near future which would conflict with operation <br />of the New Elk Mine. <br />No subsidence features were observed in the Refuse Disposal Area (RDA). According to <br />available mine maps and discussions with long -time mine personnel, this area was undermined <br />as part of the Allen Mine in the early 1960s using room - and - pillar mining methods, and recovery <br />was less than 50 %. The RDA will be located over the far northeast part of the mined area which <br />has been only partially undermined. The RDA will be located from 320 to 900 ft over the old <br />workings. <br />' Mark. C. (1999), "Empirical Methods for Coal Pillar Design," Proceedings, 2nd International Workshop on Coal <br />Pillar Mechanics and Design, Vail, CO, NIOSH IC 9448, pp. 145 -154. <br />Agapito Associates, Inc. <br />