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<br />TR-9 Geotechnical Review Memo October 23, 2025 <br /> <br /> <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us <br />Jared S. Polis, Governor | Dan Gibbs, Executive Director | Michael Cunningham, Director <br />Date: October 23, 2025 <br /> <br />To: Amy Yeldell <br /> <br />CC: Travis Marshall <br /> Russ Means <br /> <br />From: Zach Trujillo <br /> <br />RE: Mid Continent Limestone Quarry, DRMS File No. M-1982-121 <br /> Technical Revision No. 9 – Highwall Reclamation Stabilization Response Review <br /> <br /> <br />Amy, <br /> <br />As requested I have reviewed the provided geotechnical report, “Highwall Reclamation Stabilization” <br />(Report) and associated adequacy responses dated October 3, 2025 for Technical Revision No. 9 (TR-9). <br />The Report is conducted by Golden Geotechnics, Inc. (GGI) on behalf of RMR Aggregates, Inc. (RMR) <br />for the Mid-Continent Limestone Quarry (Mine). The purpose of the proposed Report is to outline a plan <br />for highwall stabilization for current site conditions in the event of revocation and forfeiture of the Mine. <br />The Report is based on the site reconnaissance and engineering analysis provided in Kildruff <br />Underground Engineering’s (KUE) report, “Failure Analyses and Stabilization Report” that was approved <br />under Technical Revision No. 6 (TR-6). For more information on the referenced KUE’s engineering <br />report, please refer to TR-6 and the Division’s associated review letters dated September 29, 2023, <br />February 6, 2024, and March 25, 2024. <br /> <br />As noted earlier in this memo, the proposed Report is based on the engineering analysis and site <br />reconnaissance conducted by KUE. Most of the site parameters and conditions are carried over to the <br />Report from the original analysis provided under TR-6. After reviewing the updated Report and provided <br />responses, the primary differences between KUE’s analysis and the Report come from an adjustment to <br />the assigned cohesion value of the interbed material and adjustment to the mechanized stabilization <br />approach based on the related stability analysis. <br /> <br />Material Strength Property - Cohesion <br /> <br />As discussed in previous memos, the material strength properties used within the Report were assumed <br />and back-calculated values used in KUE’s engineering report which was approved under TR-6. With no <br />site-specific material strength testing, material strength properties were taken from published and verified <br />typical values for the encountered limestone and interbed material at the Mine. Using conservative site <br />parameters, a back analysis was conducted by setting the factor of safety to just below 1 which is the <br />minimum criteria for a failure. The purpose of this back analysis was to corroborate the published value <br />for cohesion used in the geotechnical model. The back analysis calculated value is which is the <br />cohesion value used for the interbed material associated with the geotechnical analysis provided under <br />TR-9. Based on the conservative approach in determining the interbed material cohesion along with the