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

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May 11, 2011 Page 3 A comprehensive study of subsidence related to longwall mining in the Allen Mine was initiated in 1981. The final report for this study is dated September 19, 1982. This study obtained subsidence data (vertical and horizontal) over longwall and room - and - pillar mining areas. According to New Elk, the data obtained during this study indicate that subsidence in this area typically occurs as vertical displacement of the total overburden unit (i.e., very little differential settlement) with dampened horizontal status. Partial subsidence data indicate maximum vertical displacement of about 3 ft over a 6 -ft -high longwall panel and maximum horizontal displacement of less than 1 ft. This displacement occurred within 6 months of longwall undermining. Subsidence under room - and - pillar areas was considerably less (maximum vertical 0.3 and 1.4 ft) with most displacement occurring within 3 months. Based on the data obtained, it can be inferred that subsidence over the New Elk mine occurs quickly and in mass, with very little visible surface expression. Therefore, it is reasonable to conclude that any subsidence that may have resulted from undermining (more than 20 years ago) with pillaring and longwall extraction has already occurred and that additional subsidence resulting from placement of the refuse pile would be minimal. The stability of the refuse pile as designed (stability factor [SF] 1.5) should not be affected by subsidence. The post - mining and pre - mining land uses of the permit area are identical and are described in detail in Section 2.04.3 of the current permit. The land use is shown on Map 4, Pre - Mine Land Use, and Map 15, Surface Disturbance and Post - Mining Land Use —East Portal and Map 16, Surface Disturbance and Post - Mining Land Use —West Portal. The Operator does plan to monitor for subsidence at the New Elk mine. Mining during the permit term will be in the non - renewable resource areas as shown on Map 20 Sheets 1-3—Structure Inventory. No retreat mining will be performed under renewable resources. 3.0 SURFACE SUBSIDENCE PREDICTION Since no pillar extraction is planned under this permit and development -only mining with adequate stability factors (2.0 for mains /sub -mains pillars and 1.5 for panel pillars) is to be performed in the Apache and Allen seams, AAI anticipates that no mining- induced surface subsidence will occur. The stability of the workings was analyzed using the Analysis of Retreat Pillar Mining Stability (ARMPS) computer code developed by National Institute for Occupational Safety and Health (NIOSH) with the assumption that all workings will be development -only. The program uses the modified Mark - Bieniawski pillar stability formula' and evaluates the stability within a zone comprising a number of pillars. Appropriate pillar sizes for mains /sub -mains and panels were determined for varying cover depths and extraction thicknesses. Coal extraction from 20 -ft wide entries and crosscuts is typically not associated with trough subsidence, which is characterized by the formation of a broad and elliptical basin at the surface and is induced by total extractions over large areas. Sinkhole subsidence, progressive caving of strata from the mine roof upwards, is the only likely subsidence associated with such narrow entries. However, several studies indicate that the probability of sinkhole subsidence Mark. C. (1999), "Empirical Methods for Coal Pillar Design," Proceedings, 2nd International Workshop on Coal Pillar Mechanics and Design, Vail, CO, NIOSH IC 9448, pp. 145 -154. Agapito Associates, Inc.