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KILDUFF <br /> o.- <br /> UNDERGROUND MEMORANDUM <br /> ENGINEE RING,INC. <br /> To: Robert Wagner From: Sean Sundermann <br /> Company: RMR Aggregates, Inc. Date: June 20 2023 <br /> Project: Mid Continent Limestone Quarry Prj No.: P-23018SS <br /> Location: Glenwood Springs, CO RE: Rock Failure Analysis and Stability <br /> On behalf of RMR Aggregates, Inc. (RMRA), Kilduff Underground Engineering, Inc. (KUE) has <br /> performed an evaluation of the factors that led to the West highwall ground event and to <br /> assess the long-term stability of the east highwall in its current state.The intent is not to <br /> evaluate stability during mining operations on the East Face but is intended to determine a safe <br /> work area for performing mining operations below the East Face in its current condition. This <br /> evaluation was conducted as a step in the larger evaluation of both the current and future <br /> mining areas adjacent to the highwall ground event area. <br /> PROJECT BACKGROUND <br /> Mr. Wagner (RMRA) reported to KUE that a headwall ground event had occurred on the West <br /> Wall of the Mid Continent Limestone Quarry on January 18, 2023. KUE Principal Geologist Sean <br /> Sundermann, PG, CEG and Senior Construction Specialist Jim Johnson performed a site walk of <br /> the site on January 26, 2023 with RMRA staff to evaluate the current condition the slope and <br /> initial assessment of the root cause of the event. <br /> Regional Geology <br /> The quarry lies primarily within the Mississippian-age Leadville Limestone, a very fossiliferous, <br /> massive, coarse to finely crystalline limestone and dolomite formation, as mapped by the <br /> Colorado Geological Survey (Kirkham et al., 20081). The unit is described by Kirkham et al. as <br /> 200 feet thick in the site area. The Leadville Limestone formation consists of gray to bluish-gray, <br /> coarse to finely crystalline limestone underlain by Dolomitic limestone with 20 feet to 30 feet of <br /> varying amounts of sand expected in the basal unit. Underlying the Leadville Limestone is the <br /> Upper Devonian-age Chaffee Group. Near the southeast flank of the White River Uplift, the <br /> Gilman Sandstone, the upper unit of the Chaffee Group, is predominantly a 16-foot thick <br /> calcareous sandstone (Kirkham et al., 2008), pinching out towards Glenwood Springs. The <br /> proposed expansion area is bound to the north by a mapped bedrock graben,just south of the <br /> Glenwood monocline axis, exposing the younger fossiliferous limestone unit of the Lower <br /> 1 Kirkham, R., Streufert, R., Cappa,J.,Shaw,C.,Allen,J.,and J.Jones,2008, Geologic map of the Glenwood Springs quadrangle, <br /> Garfield County,Colorado;Colorado Geological Survey, Map Series 38,scale 1:24,000. <br /> Page. 1 <br /> 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM <br />