2008-03-21_PERMIT FILE - C1980007A (5)

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West Elk Mine Tremors generated by bumps and rock bursts in the Somerset Mine area attain magnitudes that have shaken structures in the West Elk Mine area and have been felt sometimes by West Elk Mine personnel. These local tremors may affect underground workings, landslide or potential rock fall areas, particularly during prolonged periods of increased precipitation. It is noteworthy, however, that the Rulison nuclear shot in 1969, which produced a tremor with a Richter magnitude of 5.2 (many times greater than the magnitudes of any recorded bump or rock burst), did not affect the Somerset Mine, and did not trigger any known landslides or rockfalls. In contrast to microcseismic effects generated by bumps and rock bursts that are sometimes felt at the surface a mile or more from room-and-pillar mining operations, the initial cave in a longwall panel may well generate the largest seismic event. In some longwall mines which have thick and strong roof rocks, the initial cave may not occur for several hundred feet, and thus, can generate a shock wave through the mine and overburden that can be felt at the surface for considerable distances from the mine. However, the initial observed cave in the West Elk Mine occurs in 0 to 45 feet from the start of the panel. MCC has experienced no measurable microseismic events at the surface due to initial longwall caving and bumps originating from the mine. Because roof conditions are similar in the Apache Rocks and Box Canyon mining areas, MCC does not anticipate any different microseismic effects in these areas than has been experienced in the current mining area. It is important to note that mining plans for the SOD area do not include undermining the reservoir or the escarpments adjacent to the reservoir. In fact, Minnesota Reservoir is located outside of the angle of mining influence of the nine projected panels (panels E1 through E9) for the South of i Divide mining area. The northwest corner of panel E9, which is nearest to the reservoir, is located 800 feet away. The angle of draw to this nearest area of nijuing is 69°. The angle is much greater than the maximum of 20° projected for the SOD mining area. This means neither Minnesota Reservoir or Monument Dam will not be subsided or be within the angle of draw of longwall mining in projected panel E9. The potential for landslides, rockfalls, and other seismic impacts to Minnesota Reservoir are discussed in detail in the preceding sections titled "Potential Impacts of Subsidence and Mine- Induced Seismic Activity on Landslides and Rockfalls" and "Effects Of Subsidence And Mine- Induced Seismic Activity On Man-Made Structures And Renewable Resources - Minnesota Reservoir". As stated in these previous sections, field observations during the past nine years (1996 through 2004) indicate landslide movement occurs in response to moisture and ground saturation, and is not noticeably affected by subsidence or any mine-related seismic activity caused by longwall mining beneath or near the landslides. Additionally, records of seismic events in the immediate area of the West Elk Mine provided by the NEIC indicate that since 1983, the largest event registered 3.60 on the Richter scale and occurred on June 20, 2002. No evidence was observed that this event resulted in new or renewed movement of landslides in the mine area or damage to Mlonument Dam or Minnesota Reservoir. A coal bounce measuring 3. on the Richter scale occurred in the mine area on October 10, 2004 and no impacts to surface features or structures vas noted. flistorically, coal bounces in the area have been recorded in the range of <2.0 to 3.3. None of these events appear to have impacted the area landslides, and in particular, Monument Dam or Minnesota Reservoir. As indicated in the GEI report contained in Exhibit 72, it is unlikely that mining in the SOD will result in seismic events greater than 23. 2.05-160 Revised Jayne 200.1 PRIO, Rev. Alar•ch 2006; A1ay 2006 PRIG, Alov. 2006TR107,Apri12007TR108;Sep. 2007 PR12; Feb. 2008 PR-12