2023-08-31_ENFORCEMENT - M1982121

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K1L D UFF RMR Aggregates, Inc. U N ❑ E R G R O U N ❑ Rock Failure Analyses and Stabilization Report E NGIN E E R I N G,INC. Mid Continent Limestone Ouarry Figure 3 (provided by Lewicki & Associates)with corresponding site numbers, detailed below from south to north: • Site 2: 39.57167; -107.322920, approx. elev. 7,170 ft. o Structure measurement (dip/dip direction): 34°;185. 0 15 ft thick upper/lower limestone beds. o Laterally continuous bed surface. No significant aperture or adverse interbed. o Pairs with comparable surface looking west across drainage. • Site 3: 39.57190; -107.32288, approx. elev. 7,200ft. o Upper limestone layer measured 10 ft thick. o Laterally continuous bed surface without significant aperture or interbed. • Site 4: 39.57211; -107.32257, approx. elev 7,290 ft. o Daylight of laterally continuous bedding plane. Upper limestone beds have pinched out at this line of latitude. • Site 1: 39.57250; -107.32250, approx. elev. 7,370 ft. o Structure measurement (dip/dip direc): 28°;183. o Laterally continuous joint surface (>10 meters), wavy, covered in thin talus. o Pairs with comparable surface looking west across drainage. Photos of the site locations are provided in Appendix F. Talus cover and the waviness of the bed surface limited the ability for high confidence structural measurements at some sites. The spatial intent of the slope configuration models discussed in section 6 should be to extend north to where the upper limestone layers pinch out above the current mining activities. The bedrock bedding slope, which is the boundary between the massive limestone below and the adverse limestone units above, was observed as very laterally continuous but could undulate locally creating a slight change in dip direction.To meet the established minimum FOS for the slope, using a bench slope geometry of 1.4H:1V or greater that leaves varying thicknesses of the upper limestone layers in place will likely require the use of mechanical stabilization. This is considered a lesser option for long- term stability and safety, but is considered below on an as needed basis. 8. MINE STABILIZATION A summary of the mine operation plan recommendations, from a geotechnical perspective, is provided here to inform a full mine operation plan provided by RMRA under separate cover. The overall intent is to achieve longterm slope stability by eliminating the potential for headwall failure along the upper limestone beds. The mine plan works under the assumption the upper unit planar slide failure mode , dipping to the south along the laterally continuous bedding plane, will only release in that direction. The mine plan is a phased and stepped approach working from the southwest corner of the headwall to the northeast with the intent to eliminate the possibility of permanent or temporary condition of the upper limestone in the cutslope wall. It is the opinion of WE that the upper limestone layer should be removed completely from the highwall to minimize the risk of another release. This can be performed via multiple mining methods. Page 13 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM