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West Elk Mine mining area. Earth tremors have been recorded or felt by local residents in the Somerset area since the eazly 1960s. The tremors commonly aze the result of coal mine bumps and rock bursts, which aze spontaneous releases of strain energy in highly stressed coal and rock. In the Somerset Mine azea before closure, the bumps and rock bursts were common in room-and-pillar mining azeas where stresses concentrated within isolated pillazs and blocks of coal. Earth tremors have continued sporadically in the Somerset Mine azea since the mine was closed. Tremors generated by bumps and rock bursts in the Somerset Mine area attain magnitudes that have shaken structures in the West Elk Mine azea and have been felt sometimes by West Elk Mine personnel. These local tremors may affect underground workings, landslide or potential rock fall azeas, particulazly 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 aze sometimes felt at the surface a mile or more from room-and-pillaz mining operations, the initial cave in a longwall panel may well generate the lazgest 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 aze similar in the Apache Rocks and Box Canyon mining areas, MCC does not anticipate any different microseismic effects in these azeas than has been experienced in the current mining azea. It is important to note that mining plans for the SOD azea 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 El through E9) for the South of Divide mining azea. The northwest corner of panel E9, which is neazest to the reservoir, is located 800 feet away. The angle of draw to this neazest azea of mining 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 aze 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 yeazs (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 neaz 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 2.05-159 Revised June 2005 PR/0, Rev. March 2006; May 2006 PRIO