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December 27, 2023 Page 1-1 <br />Agapito Associates, Inc. <br />1 INTRODUCTION <br />This report provides the assessment of the geotechnical parameters associated with secondary <br />pillar extraction in the E Seam in Sunset Mains South between crosscuts 2 and 30 (see Figure 1- <br />1). Following discussions with Arch West Elk (West Elk Mine), a comprehensive review of the <br />geotechnical environment, and the consideration of the mining constraints for the panel, Agapito <br />Associates, Inc. (Agapito) has made recommendations for maximum pillar extraction. Agapito <br />considered the following requirements: <br /> Pillar extraction will not take place at depths of cover less than 250 feet (ft). <br /> Pillar extraction will stop one crosscut outby of the BF Fault at the outby end of Sunset <br />Mains South. <br /> In order to maintain a bleeder system around areas of gob and to inspect inby seals, a single <br />life-of-mine roadway must remain travelable during and after pillar extraction activities. <br /> The pillars will be extracted in their current state and, as such, additional development and <br />roof bolting should not be considered for preparation in the pillar extraction plan. <br /> To avoid unstable remanent pillars, the pillar extraction should aim to mine as much of the <br />pillar as practically possible. <br /> If a large percentage of the pillar remains following extraction, the remaining pillar should <br />be classed as long-term stable. <br /> <br />The geotechnical environment was characterized from geological and geotechnical information <br />provided by West Elk Mine, including borehole logs from drillholes in the vicinity of the panel, <br />geological structure drawings, surveyed mine plan drawings, and overburden depth contour <br />boundaries. Agapito also drew on its extensive experience of ground condition characterization <br />and geotechnical design in the E Seam at the mine. <br />The pillar stability assessment utilized industry standard empirical pillar design formula and <br />criteria. The numerical model program LaModel was used to assess the detailed stress environment <br />during pillar extraction following extraction of the pillars in the panel. <br />Surface subsidence modeling was carried out using the Surface Deformation Prediction System <br />(SDPS) to estimate maximum surface displacement following pillar extraction in the panel. <br />