2011-05-18_PERMIT FILE - C1981012A (2)

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May 11, 2011 Page 18 • The room - and - pillar development plan should be re- evaluated to ensure that operations will not further damage the structure in question. 4.14 Purgatoire River Alluvial Valley Floor 4.14.1 Alluvial Valley Floor Subsidence Control Plan The current mining plan under the Purgatoire River and associated alluvial valley floor are development -only workings and do not have any retreat panels. The extraction ratio is also planned to be less than 50% for these workings. Disturbed area boundaries and stream buffer zones have been clearly marked and will be maintained in accordance with Section 4.02 and 4.06 of the CMLRD Regulation for Coal Mining. According to New Elk officials, stream buffer zone signs have been placed in high traffic areas on site and will be placed along the entire length of the Purgatoire River within the permit boundary. Planned Allen Seam mains to be developed under the alluvial bed will have seven 20 -ft- wide entries and 65 -ft x 75 -ft pillars (center -to- center). The mains have a stability factor of 4.0, for development in 4.5 -ft -thick coal at a depth of 500 ft. This geometry results in an extraction of 49 %. Other pillar designs may ultimately be considered, but in no case will the design ARMPS stability factor be less than 2.0 and extraction ratio be more than 50 %. No material damage to renewable resource lands has been recorded which can be attributed to past mining at the New Elk mine in the 1980s. No discernible effects can be attributed to subsidence induced by the old New Elk workings as evidenced 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, given the low extraction ratios and adequacy of cover depth between them and the underground workings. In addition to the above - mentioned mining controls, the following mitigation and monitoring plan is recommended. 4.14.2 Alluvial Valley Floor Monitoring Plan To ensure that the control plan is effective, the following monitoring plan is recommended: • A pre - mining survey of the alluvial bed within a 10° angle of draw, from the planned Allen Seam workings, should be performed to collect baseline alluvial morphology. • Monthly visual observation of the alluvium within the monitoring area should be performed once the development workings are within a 10° angle of draw, from the planned Allen Seam workings, until two months after development has advanced directly beneath. • Any unusual large crater or crack formation in the alluvium should be noted. Agapito Associates, Inc.