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Geotechnical Stability Exhibit <br /> Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry <br /> <br /> January 2024 | 3 <br />1 Introduction <br />1.1 Purpose and Scope <br />This Geotechnical Stability Exhibit (Exhibit) presents the results of HDR Engineering, Inc.’s <br />(HDR’s) geotechnical evaluation for the highwall configurations in the Holcim Morrison Quarry <br />mine near Morrison, Colorado. The work completed has been performed under HDR’s Scope of <br />Work agreement with Holcim (previously Aggregate Industries) dated May of 2022. This quarry <br />is currently operating under Permit M-1973-021 from the Colorado Division of Reclamation <br />Mining and Safety (DRMS), with the existing Permit M-1973-021 Amendment No. 7 (AM-07). <br />The Geotechnical Stability Exhibit prepared by GEI, Inc., dated November of 2020, is included <br />as an appendix to the existing permit. This Exhibit has been prepared to supplement the DRMS <br />Permit M-1973-021 Technical Revision No. 9 (TR-09) and summarizes stability analyses <br />performed to evaluate proposed quarry configurations in relation to the minimum required <br />Factor of Safety (FoS) for rock slope stability per DRMS’s Mined Land Reclamation Boards <br />(MLRB) Policy 30, dated 2018. <br />The following Scope of Work (SOW) was executed by HDR as part of the South Quarry <br />evaluation. <br />· Perform a subsurface exploration of the South Quarry to confirm historic subsurface <br />data. <br />· Develop a 3D model of the South Quarry using available data from previous subsurface <br />explorations and data collected recently by HDR. <br />· Review and provide additional laboratory testing results. <br />· Conduct geotechnical analysis to determine FoS for various anticipated bench <br />configurations for mining of the South Quarry from elevations 6600’ to 6200’. <br />1.2 Site Description <br />The Morrison Quarry is a hard rock aggregate mine located west of Colorado Highway 8 and is <br />approximately 0.5 miles north of U.S. Highway 285 in Morrison, Colorado. The mine location is <br />shown in Figure 1, below, and is located west of the Dakota hogback along the Colorado Front <br />Range, west of Denver. The quarry consists of three mining cells, which include the North, <br />Central, and South Quarries. The North and Central Quarries are currently in the reclamation <br />phase, whereas the South Quarry is active. The approximate extents of these mining cells are <br />shown in Figure 2, below.