2024-02-01_REVISION - M1973021 (2)

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Geotechnical Stability Exhibit Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry January 2024 | 8 3 Field Evaluations Prior to HDR’s involvement with the quarry, numerous field evaluations were performed by Lyman Henn, Holcim (conducted as former Aggregate Industries), GEI, and Tetra Tech. In total, 28 geotechnical borings were performed within the South Quarry since 2005. A full summary of the drilling efforts and locations are provided in GEI’s Permit M-1973-021 AM-07 Geotechnical Stability Exhibit. The results of those evaluations have been included along with recent HDR evaluations, to develop the design and recommendations included in this report. The following sections summarize the effort by HDR to support the design and recommendations included in this report. A Boring Location Map of historic and recent borings at the Morrison Quarry is included in Appendix A. 3.1 Annual Quarry Inspections HDR was contracted in 2021 and 2022 to assist in preparing the Annual Geotechnical Addendums as required by Permit M-1973-021 Amendment No. 3 (AM-03) and carried forth in subsequent amendments to the current Permit M-1973-021 AM-07. These Addendums allow the DRMS to review existing and evolving quarry conditions at the Morrison Quarry. As part of these Addendums, HDR staff performed onsite inspections to document exposed rock conditions such as joint and foliation orientations, shear zones, intrusions, and rock types for areas mined in the respective calendar year. The Geotechnical Scanline data was incorporated with the geotechnical boring data to develop a conceptual model regarding the structure and quality of the bedrock currently exposed and anticipated to be encountered during mining. Refer to the 2021 and 2022 Morrison Quarry Geotechnical Addenda for a summary of the findings during the annual inspections. 3.2 2022 Geotechnical Borings A total of five (5) borings were drilled during the 2022 explorations. One (1) of the borings was advanced for a forthcoming groundwater pump test, and was therefore drilled using destructive methods and not included in the borings utilized for design. The remaining four (4) borings were performed by Authentic Drilling, Inc, of Kiowa, CO. Core samples of the underlying rock were collected utilizing HQ sized wireline to depths ranging from 380.2 to 401.0 feet below ground surface (bgs), and were performed between July 6, 2022, and July 22, 2022. HDR provided drilling oversight and logged the core recovery and strata. Refer to Table 1 below for a summary of the geotechnical borings performed for the Morrison Quarry, and Appendix A, Subsurface Exploration Findings for the 2022 Geotechnical Boring Logs.