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West Elk Mine <br /> <br />2.05-120 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; <br /> 12/20- TR149; 12/21- TR150, 1/24-TR152 <br />movement of the landslide located on the left abutment of the dam. The construction and <br />implementation of these structures and activities will allow the dam to withstand a seismic event <br />of at least magnitude 2.3 (Richter scale) generating a peak ground acceleration (pga) of 0.16 g. <br />As stated in the GEI report, a maximum seismic event and pga anticipated to be generated by <br />mining in the SOD will be ML 2.3 and 0.06 g, respectively. Barr Engineering evaluated the <br />stability of the newly constructed dam during the Summer of 2008 (see Exhibit 76) and verified <br />that the safety factor of 1.5 and would not be impacted by mining-induced seismicity. <br />Subsidence Control Plan - 2.05.6 (6)(b)(iii)(B), (6)(d)(i&ii), (6)(e)(iv) & (6)(f)(i-vii) <br />Description of Mining Methods – 2.05.6 (6)(f)(iv)( A& B) <br />As discussed in Section 2.05.6(6)(e)(i)(A), Brief Description of Mining Method, the longwall <br />mining method is planned for the SOD, Apache Rocks West, Southern Panels and Sunset Trail <br />mining areas. A general east-west panel layout, is planned except for the E-seam longwall panels <br />LWE16 and LWE17 that will be in a north-south orientation. Although longwall mining may <br />initially induce more caving and fracturing of the roof rocks, it offers the advantages of maximizing <br />resource recovery. The longwall method also causes more uniform subsidence (full extraction of <br />panel) and causes equilibrium conditions to be reached in a shorter period of time (i.e., there is no <br />additional, lingering pillar crushing in panels). See further discussions in the current version of <br />Exhibit 60E. <br />Also as discussed in Section 2.05.6(6)(e)(i)(A), Brief Description of Mining Method, retreat mining <br />of the Sunset South Mains will be utilized in the Sunset Trail Mining area. Exhibit 84, the <br />Geotechnical Assessment For The Purpose Of Pillar Extraction Between 2 And 30 Crosscuts In <br />Sunset South Mains, dated December 27, 2023, and the Geotechnical Assessment For The Purpose <br />Of Partial Pillar Extraction Between 2 And 29 Crosscuts In Sunset Mains, dated April 22, 2024, <br />analyzes and depicts detailed mining sequences, modelling parameters, subsidence predictions and <br />minimum and maximum depths of cover for retreat mining in the Mains. <br />Although subsidence is primarily a result of the secondary recovery of coal from a longwall coal <br />panel, subsidence type features may occur when developing main entries/roadways under <br />shallow, unconsolidated and saturated cover. Such was the case in October 2020 when <br />developing main entries under South Prong Creek. To avoid similar issues in the future, MCC <br />has performed an analysis of the minimum depth of cover required for development mining in <br />the West Elk Mine to avoid the potential for this type of surface subsidence impacts. MCC will <br />adhere to the recommendations for development mining beneath perennial streams as detailed in <br />Appendix A of Exhibit 60E. <br />Preventive Measures – 2.05.6(6)(f)(iii) <br />State-of-the-art longwall mining technology will continue to be utilized for extraction of the B <br />Seam and E Seam coal within the permit area. Although longwall mining may initially induce <br />more caving and fracturing of the roof rocks, as compared to the room-and-pillar method, it <br />offers the advantages of maximizing resource recovery; more complete subsidence; equilibrium <br />conditions occurring in a shorter period of time; more uniform and predictable parameters <br />necessary for the evaluation of probable hydrologic consequences; and in general, fewer and less <br />significant adverse hydrologic impacts than room-and-pillar mining.