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Morrison Quarry AM-07 Geotechnical Stability Exhibit <br /> DRMS Permit M-1973-021 <br /> Aggregate Industries WCR Inc. <br /> Objective: Develop strength parameters for Precambrian bedrock at Morrison Quarry's South <br /> Quarry to support highwall stability evaluations. The stability evaluations will focus on <br /> localized benches as well as global highwall failures. <br /> Background: Aggregate Industries(AI) owns and operates the Morrison Quarry near Golden, <br /> Colorado. Morrison Quarry is a hard rock aggregate mine that produces materials by <br /> blasting bedrock from steep highwalls and hauling materials to an on-site crushing and <br /> processing plant. The site contains four separate quarries shown in Figure 1, and their <br /> current status is summarized below: <br /> Quarry ID Status <br /> North Quarry Mining is complete, quarry is reclaimed. <br /> Provides water storage for Town of Morrison. <br /> Central Quarry Mining is complete, currently used for stockpiles. <br /> Reclamation pending. <br /> South Quarry Currently being mined. <br /> Upper slopes have been reclaimed. <br /> West Quarry Undeveloped, Al looking to develop West Quarry in <br /> 2021. <br /> Al intends to increase the highwall slope at the South Quarry to mine additional <br /> reserves from existing highwall benches below El. 7000. Future excavations in the <br /> quarry floor are also intended to be steeper than the currently permitted <br /> highwall/bench configuration of 40-feet high, 40-feet wide benches. Al is seeking to <br /> increase the maximum bench height to 70-feet and reduce the bench width to 30-feet <br /> or less based on results of stability evaluations. <br /> Photos 1 and 2 were taken by GEI's unmanned aerial vehicle and show the condition of <br /> the highwall as of December 2019. <br /> Geologic Setting: <br /> Bedrock at Morrison Quarry is primarily composed of Precambrian granitic gneiss and <br /> biotite gneisses, with localized zones of sillimanitic gneiss. The granitic gneiss is <br /> characterized by mineral composition and is primarily composed of fine to medium <br /> grained feldspars, quartz, and biotite, pyroxene, and amphibole,and contains thin <br /> foliations generally 1cm thick or less. The biotite gneiss is similar to the granitic gneiss <br /> but contains less feldspar and quartz. The sillimanitic gneiss is fine to medium grained <br /> but also contain the mineral sillimanite, which is a product of secondary mineralization. <br /> The sillimanitic gneiss is not sold by the mine due to its low durability, and is instead <br /> discarded and stockpiled on site, and may be used in the future for reclamation <br /> purposes. Available laboratory data on the sillimanitic gneiss does not show a marked <br /> decrease in unconfined compressive strength or shear strength test results, but most <br /> failures are related to outcrops or exposures of the sillimanitic gneiss. A cut slope in the <br /> Central Quarry reveals a 10-to 15-foot-thick band of sillimanitic gneiss, and outcrops of <br /> sillimanitic gneiss have been highlighted and included in geologic maps prepared by GO <br /> GEI Consultants, Inc. 1 of 25 Appendix C.1 <br /> November 2020 <br />