2023-08-31_ENFORCEMENT - M1982121

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WL D UFF RMR Aggregates, Inc. U N ❑ E R G R 0 U N C Rock Failure Analyses and Stabilization Report ENGIN E E R I N G,INC Mid Continent Limestone Quarry 1. PROJECT BACKGROUND 1.1. GENERAL DESCRIPTION A headwall ground event occurred on the West Wall of the Mid Continent Limestone Quarry (Figure 1) on January 18, 2023. Mr. Robert Wagner of RMR Aggregates, Inc. (RMRA) reached out to Kilduff Underground Engineering, Inc. (KUE) the following day to discuss the potential causes of failure. KUE Principal Geologist Sean Sundermann, PG, CEG and Senior Construction Specialist Jim Johnson performed a site walk of the site on January 26, 2023 with RMRA staff to evaluate the current condition the slope and initial assessment of the root cause of the event. At that time a general scope of work was developed to evaluate the geotechnical factors that led to the West highwall ground event and to assess the long-term stability of the West and East sides of the highwall in its current state. This report is the program deliverable that delivers on the following scope of work items: • Description of findings from multiple site reconnaissances; • Kinematic analyses of failure modes; • Long Term Steady-State stability analysis; • Rockfall modeling; • Rockfall mitigation recommendations for current configuration; • Geotechnical input to long-term stabilization plan; and • Mechanical stabilization scheme. Results and findings of the above scope of work are summarized in the report sections below. Photos, field measurements, and model runs from multiple analyses are provided in the attached appendices: Appendix A—2023 Field Photographs Appendix B— Discontinuity and Structure Measurements Appendix C— Kinematic Analyses Appendix D— Planar Failure Appendix E— Rockfall Modeling Appendix F—July 2023 West Face Field Photographs Appendix G—Active Stabilization Design 1.2. REGIONAL AND QUARRY GEOLOGY The quarry lies primarily within the Mississippian-age Leadville Limestone, a very fossiliferous, massive, coarse to finely crystalline limestone and dolomite formation, as mapped by the Colorado Geological Survey (Kirkham et al., 20081). The unit is described by Kirkham et al. as 200 feet thick in the site area. The Leadville Limestone formation consists of gray to bluish-gray, coarse to finely crystalline limestone underlain by Dolomitic limestone with 20 feet to 30 feet of varying amounts of sand expected in the basal unit. Underlying the Leadville Limestone is the Upper Devonian-age 1 Kirkham, R., Streufert, R., Cappa,J.,Shaw,C.,Allen,J.,and J.Jones,2008, Geologic map of the Glenwood Springs quadrangle, Garfield County,Colorado;Colorado Geological Survey, Map Series 38,scale 1:24,000. Page 1 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM