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Geotechnical Stability Exhibit ��� <br /> Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry <br /> 3 ield Evaluations <br /> Prior to HDR's involvement with the quarry, numerous field evaluations were performed by <br /> Lyman Henn, Holcim (conducted as former Aggregate Industries), GEI, and Tetra Tech. In <br /> total, 28 geotechnical borings were performed within the South Quarry since 2005. A full <br /> summary of the drilling efforts and locations are provided in GEI's Permit M-1973-021 AM-07 <br /> Geotechnical Stability Exhibit. The results of those evaluations have been included along with <br /> recent HDR evaluations, to develop the design and recommendations included in this report. <br /> The following sections summarize the effort by HDR to support the design and <br /> recommendations included in this report. <br /> Annual Quarry Inspections <br /> HDR was contracted in 2021 and 2022 to assist in preparing the Annual Geotechnical <br /> Addendums as required by Permit M-1973-021 Amendment No. 3 (AM-03) and carried forth in <br /> subsequent amendments to the current Permit M-1973-021 AM-07. These Addendums allow <br /> the DRMS to review existing and evolving quarry conditions at the Morrison Quarry. As part of <br /> these Addendums, HDR staff performed onsite inspections to document exposed rock <br /> conditions such as joint and foliation orientations, shear zones, intrusions, and rock types for <br /> areas mined in the respective calendar year. The Geotechnical Scanline data was incorporated <br /> with the geotechnical boring data to develop a conceptual model regarding the structure and <br /> quality of the bedrock currently exposed and anticipated to be encountered during mining. <br /> Refer to the 2021 and 2022 Morrison Quarry Geotechnical Addenda for a summary of the <br /> findings during the annual inspections. <br /> 2022 Geotechnical Borings <br /> A total of five (5) borings were drilled during the 2022 explorations. One (1) of the borings was <br /> advanced for a forthcoming groundwater pump test, and was therefore drilled using destructive <br /> methods and not included in the borings utilized for design. The remaining four (4) borings were <br /> performed by Authentic Drilling, Inc, of Kiowa, CO. Core samples of the underlying rock were <br /> collected utilizing HQ sized wireline to depths ranging from 380.2 to 401.0 feet below ground <br /> surface (bgs), and were performed between July 6, 2022, and July 22, 2022. HDR provided <br /> drilling oversight and logged the core recovery and strata. Refer to Table 1 below for a <br /> summary of the geotechnical borings performed for the Morrison Quarry, and Appendix A, <br /> Subsurface Exploration Findings for the 2022 Geotechnical Boring Logs. <br /> Table 1 —Summary of 2022 Borings <br /> Completion Approximate Total <br /> Boring Date Northing Easting Elevation (ft.) Depth <br /> (ft.) <br /> HDR-002 7/12/2022 1653224.052 3083166.334 6602.3 380.2 <br /> HDR-003 7/20/2022 1653191.774 3082950.6 6604.5 391.0 <br /> May 2023 1 8 <br />