2012-02-13_REVISION - C1981012 (8)

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The renewable resource lands existing in the form of the Purgatoire River and associated alluvial valley floor are unlikely to be impacted by any anticipated subsidence in the mining plan. The locations of these renewable resources are shown on Map 20. The description of the renewable resource lands is in Exhibit 8. The current mining plan under the State Highway 12, the Purgatoire River and associated alluvial valley floor are development -only workings and do not have any retreat panels. The extraction ratio is planned to be less than 50% for these workings. The stability of development -only workings, as well as retreat panel workings was analyzed using the Analysis of Retreat Pillar Mining Stability (ARMPS) computer code developed by NIOSH. The program uses the modified Mark - Bieniawski pillar stability formula and evaluates the stability within a zone comprising a number of pillars. Development -only pillar dimensions were developed for areas such as underneath the renewable resource lands mentioned above, and areas with cover depth and mining height combinations that precluded the use of retreat mining. Stable panel pillar dimensions were developed for various cover depth and mining height combinations using ARMPS. The details of this analysis are included in Exhibit 24. If subsidence has occurred in the permit area, caused by past mining, no material damage to structures or renewable resource land has occurred. No discernible effects can be attributed to subsidence induced by the old New Elk Mine workings. This is supported by the stable condition of the Colorado & Wyoming Railroad right -of -way and Colorado Highway 12. Any effect of subsidence on the renewable resource lands located in the Purgatoire River area is considered unlikely. There are no structures that will be undermined using retreat methods and subsided in this permit application. The details of structures 44, 45, 46, and 47 are shown in relation to the permit boundary and mine plan in Figure 19. Mining detail, showing development -only mining areas and retreat (pillar recovery) mining, is shown on MAP 3 Mine Plan. The gas wells will be protected by a barrier pillar. Gas and water pipelines associated with the gas wells will be protected by a corridor in which no retreat mining will occur. At the extents of each of the panels, a bleeder entry is left in place to maintain the ventilation system. Pillars will not be recovered in the bleeder entry. Structures (and their owners) to be undermined by room and pillar development methods only are listed below. Detail numbers are drawn from Map 20, Sheet 1-New Elk Mine Structure Inventory Map. Exhibit 42 includes a table of all of the structures in the permit boundary. • Alluvial valley floor • Highway 12 • Purgatoire River • Irrigated pasture land (Vigil) • Detail 1— Pipelines and roads to 35 -13 New Elk (XTO Energy) • Detail 3— Pipelines and roads to 35 -16 New Elk (XTO Energy) PR -04 2.05 -93 Revised 02/09/12