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F)� <br /> March 1, 2021 <br /> Amy Eschberger <br /> Environmental Protection Specialist <br /> Colorado Division of Reclamation, Mining and Safety <br /> 1313 Sherman Street, Room 215 <br /> Denver, CO 80203 <br /> RE: Lyons Quarry; DRMS File No. M-1 977-141; Technical Revision No. 5; <br /> Verification of Grading Plan <br /> Dear Ms. Eschberger, <br /> This letter is to verify that the slopes and overall configuration shown on the Final Grading Plan <br /> presented in Technical Revision No. 5 meet the geotechnical specifications of the 2008 Kleinfelder <br /> Summary Report of Engineering Stability Analysis (Kleinfelder Report)or that additional analysis has <br /> been performed to show that conservative factors of safety have been met. <br /> The Kleinfelder Report states that where the highwall and rock slopes will remain exposed, the final <br /> reclamation slopes can have the following configuration: <br /> • Dacite left at existing slope angle with loose rock scaled from the face of the dacite. <br /> • Fountain Formation laid back to a single overall slope angle of 1.5H:1 V(33 degrees from the <br /> horizontal). <br /> • Rockfall catchment berm on minimum 20-foot-wide bench, constructed at the toe of the <br /> Fountain Formation and on top of the dacite sill at the contact of the two units. <br /> • Rockfall catchment berm on minimum 20-foot-wide bench, reclaimed or constructed at existing <br /> benches and at the toe of the dacite unit. <br /> Technical Revision No. 5 includes technical specifications covering scaling of loose rock from the dacite <br /> highwall as well as a provision for rock reinforcement to be installed where necessary for stability at the <br /> discretion of the on-site geotechnical engineer overseeing construction.The Fountain Formation will be <br /> laid back to a single overall slope angle of 2H:1 V(26.5 degrees)which is less steep than the Kleinfelder <br /> Report requirement. Due to the change to the Fountain Formation slope angle, restricted access to the <br /> rockfall catchment area, and additional analysis using the Colorado Rockfall Simulation Program <br /> (CRSP) using an updated slope configuration, a bench and berm at the toe of the Fountain Formation <br /> as well as a berm along the reclaimed bench within the dacite are not necessary for public safety. At <br /> Quarry 1 a 30-foot-high berm will be constructed to connect the existing slopes opposite of the highwall <br /> to create a large catchment basin for any rockfall from either the dacite or the laid-back Fountain <br /> Formation with a conservative factor of safety. At Quarry 2 backfill will be placed against the dacite <br /> highwall as discussed below.At the base of the dacite highwall between Quarry 1 and Quarry 2 a <br /> roughly 20-foot-high catchment berm will be constructed a minimum of 20 feet from the toe of the <br /> highwall. <br /> Quarry 2 has been partially backfilled as noted in Technical Revision No. 3.Technical Revision No. 5 <br /> provides for the completion of backfilling Quarry 2 up to the contact of the dacite with the Fountain <br /> Formation, above which the Fountain Formation will be laid back to 2H:1 V, along the east slope. The <br /> south and west slopes of Quarry 2 will be filled up to the crest of the Fountain Formation to create a <br /> natural swale that existed pre-mining. The Kleinfelder Report states that the existing highwall and rock <br /> idrinc.com <br /> 1670 Broadway,Suite 3400,Denver,CO 80202-4824 <br /> (303)764-1520 <br /> 1 <br />