2024-01-22_PERMIT FILE - C1980007A (4)

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West Elk Mine 2.05-115 Rev. 06/05- PR10, 03/06- PR10, 05/06- PR10, 11/060- TR107, 04/07- TR108, 09/07- PR12, 02/08- PR12; 11/10- MR372; 10/20- MR-452; 12/20- TR149; 12/21- TR150, 1/24-TR152 Based on mapping and observations by Mr. Dunrud in the B Seam of the Somerset Mine, impacts to the coal and rocks below the mined coal bed are expected to be limited to about one mining thickness. Impacts to the floors of the mine workings are expected to be limited to the chain pillars, because the floors of the longwall panels are loaded with caved roof rocks and overlying strata before deformation in the floor can occur. Floor heaving, pillar punching (the pillar punches into the floor and roof rocks), and squeezing (plastic flowage, see Dunrud 1976 for more details) are the only expected deformation in the immediate mine floor, which consists of impure coal, shale, sandstone and claystone. Deformation in the floors of the chain pillars is expected to occur after the longwall panel is mined and the pillars begin to yield. Possible Subsidence Consequences Southern Panels, SOD, Apache Rocks West, Dry Fork and Sunset Trail Mining Areas – Modeled and predicted subsidence impacts for the mining areas has been provided in the Exhibit 60 through 60E series as well as Exhibit 84. Subsidence features observed to date have been reported in MCC’s subsidence monitoring reports that have been submitted quarterly to the CDRMS as required. Potential Impacts from Local Seismic Activity Earth tremors have been recorded or felt by local residents in the Somerset area since the early 1960s. The tremors commonly are the result of coal mine bumps and rock bursts, which are spontaneous releases of strain energy in highly stressed coal and rock. In the Somerset Mine area before closure, the bumps and rock bursts were common in room-and-pillar mining areas where stresses concentrated within isolated pillars and blocks of coal (called bump blocks). Earth tremors have continued sporadically in the Somerset Mine area 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 area and have been felt sometimes by West Elk Mine personnel. These local tremors may affect underground workings, landslide or potential rockfall 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, was many times greater than the magnitudes of any recorded coal bump. To Mr. Dunrud’s knowledge, the Rulison nuclear shot did not trigger any known landslides, rockfalls, did not affect the Somerset Mine, neither did it impact reservoirs, ponds, nor streams in the Southern Panels mining area. In contrast to microseismic 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 has occurred 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.