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West Elk Mine <br />would likely be through linear zones of structural weakness (i.e., fractures, joints) which <br />may have caused the canyon to form initially. It is believed, however, that fractures and <br />joints will terminate in the soft, ductile shale and claystone units. <br />2. Cracks could locally form and be as much as 75 to 200 feet deep above chain pillars and <br />barrier pillars on the precipitous slopes, ridges, and/or cliffs that flank West Flatiron and <br />may accelerate the naturally-occurring rack fall and landslide process. <br />The worst possible, but again very unlikely, underground impacts in the Apache Rocks and the <br />Box Canyon mining azeas may be that: <br />1. Interconnected fractures in the fractured zone may form in the Marine Sandstone that <br />underlies the D-Seam and impact isolated groundwater that may be presem. Any water <br />presem in these lenticular sand units of the Marine Sandstone might therefore be diverted <br />to the mine workings. <br />2. Though unlikely, fractures filled with water and methane that were reported in the <br />abandoned Oliver No. 2 Mine (Dunrud 1476, p. 30-34) might be encountered or <br />intersected by the B-Seam fractured zone that may divert the water and methane to the B- <br />Seam workings. <br />Poteruial Impacts)`i-om Local Seismic Activity <br />.~ Earth tremors have been recorded or felt by local residents in the Somerset area since the eazly <br />1960s. The tremors commonly are the result of coal mine bumps and rock bursts, which are <br />spontaneous releases of strain energy in highly stressed coal and rock. In the Somerset Mine area <br />before closure, the bumps and rock bursts were common in room-and-pillar mining areas where <br />stresses concentrated within isolated pillars and blocks of coal. Earth tremors have continued <br />sporadically in the Somerset Mine area since the mine was closed. <br />Tremors generated by bumps and rock bursts in the Somerset Mine area attain magnitudes that <br />have shaken structures in the West Elk Mine area and have been felt sometimes by West Elk <br />Mine personnel. These local tremors may affect underground workings, landslide or potential <br />rock fall areas, particulazly during prolonged periods of increased precipitation. It is noteworthy, <br />however, that the Rulison nuclear shot in 1969, which produced a tremor with a Richter <br />magnitude of 5.2 (many times greater than the magnitudes of any recorded bump or rock burst), <br />did not affect the Somerset Mine, and did not trigger any known landslides or rockfalls. <br />In contrast to seismic effects generated by bumps and rock bursts that aze sometimes felt at the <br />surface a mile or, more from room-and-pillar mining operations, the initial cave in a longwall <br />panel may well generate the lazgest seismic event. In some longwall mines which have thick and <br />strong roof rocks, the initial cave may not occur for several hundred feet, and thus, can generate a <br />shock wave through the mine and overburden that can be felt at the surface for considerable <br />distances from the mine. However, the initial observed cave in the West Ells Mine occurs in 0 to <br />-'" , <br />U <br />2.05-132 RevisedJw. 1995 PR06; 1/96RN03; RevisedJa2 1998 PR08 <br />