2022-09-29_PERMIT FILE - C1980007 (5)

Home Browse Search

Subsidence Evaluation for the Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 33 831-032.923 Wright Water Engineers, Inc. December 2021 8. This area is located on the east side of the main Deep Creek channel above longwall panel E3. This area is identified as having low to moderate rockfall potential. It is located in an area too remote for any access roads or manmade features. Following mining in these longwall panels, no additional rockfall was observed during semi-annual field studies. 9. This area is located on the eastern boundary of the Deep Creek watershed. This rockfall area would have been over the eastern ends of panels E3, E4, and E5 if mined to the maximum projected potential extent. However, based on where mining stopped in these panels, the rockfall areas were outside the influence of mining. Of the areas listed above, most occur near local drill roads or agricultural access roads, which have only local, limited traffic on them. Any rocks that may fall in these areas could be readily removed before local traffic is impacted, should rockfalls occur on these remote roads. Evidence of naturally occurring rockfalls, such as remnant boulders located at the base of steep slopes, or in the run-out zones of these areas, and documentation of these areas prior to mining is recommended. Based on semi-annual observations in the Apache Rocks, Box Canyon, Southern Panels, and Sunset Trail mining areas, subsidence and any seismic activity caused by longwall mining is not expected to significantly affect rockfall areas with an estimated high to low rockfall potential. Only rockfall areas with an estimated very high rockfall potential were noticeably affected. However, because there are no rockfall areas with an estimated very high rockfall potential in the Southern Panels and Sunset Trail mining areas, the planned longwall panels in these mining areas will most likely not affect rockfall areas. 10.3 Importance of Baseline Landslide and Rockfall Data The most significant landslide in the Southern Panels mining area, in terms of proximity to man- made structures, is located above the northern part of E-seam longwall Panels E16 and E17 (Map 1). Although there is a large landslide within the area of mining influence of the southeast corner of E-seam longwall panel E8 (mostly in the NE¼ of Section 8), the landslides located north and south of Minnesota Reservoir are the most important in the mining area. Existing, natural (baseline) conditions are monitored before mining begins in order to document their natural state. The cracks, bulges, and depressions observed in the landslide areas north and south of Minnesota Reservoir are much more extensive and dramatic than those caused by subsidence. The vertical aerial photographs obtained by the West Elk Mine (dated July 2, 2004) provide good baseline images of all the natural, pre-mine features in the Southern Panels mining area. Observations made by WWE in the area of the West Elk Mine indicate that mining may accelerate the natural landslide process, where there are landslides that have already become unstable. However, annual observations of the surface cracks and depressions in the landslide area on Jumbo Mountain above mined B-seam longwall panels 8 and 9 determined that landslides are very likely only related to natural mass-gravity movements and not related to mining. Baseline observations and photographs have been gathered in the areas with low to moderate rockfall potential that are listed in Section 10.2 prior to mining activities. Evidence of naturally occurring rockfalls, such as remnant boulders of the base of steep slopes, or in the run-out zones of these areas with a rockfall potential have been documented prior to mining.