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J-2 Contracting Co.—DPG Pit— Technical Revision No. 1 Adequacy Review Response <br /> File No. M-2019-028 <br /> -7- <br /> Case 3- Cache La Poudre River <br /> The mining operation (Phase 3 silt pond) is adjacent to the Cache la Poudre River on the <br /> north side of the mining site. The mining depth was assumed to be 60 feet in this area <br /> based on bore log information in the geotechnical report. The minimum mining setback <br /> was set 150 feet from the river bank. <br /> At a setback of 150 feet, the resulting safety factor of 2.39 exceeds the MLRB minimum <br /> requirement of 1.50 for an embankment adjacent to a critical structure. The resulting <br /> safety factor of 1.76 is above the MLRB minimum requirement of 1.30 for an embankment <br /> subject to earthquake loading. Assuming the silt pond is full of water provides greater <br /> safety factors, 2.77 under static loading and 1.78 under earthquake loads. The proposed <br /> setback of 150 feet from the river bank is satisfactory. <br /> Case 4- Gas Line Easement <br /> The mining operation (Phase 1 silt pond) is adjacent to a pipeline easement along the <br /> east side of the mining site. The mining depth was assumed to be 85 feet in this area <br /> based on bore log information in the geotechnical report. The proposed mining setback <br /> was set 50 feet from the pipeline easement. <br /> Case 4 - At a setback of 50 feet, the resulting safety factor of 1.52 exceeds the MLRB <br /> minimum requirement of 1.50 for an embankment adjacent to a critical structure. The <br /> resulting safety factor of 1.30 is equal to the MLRB minimum requirement of 1.30 for an <br /> embankment subject to earthquake loading. Assuming the silt pond is full of water <br /> provides greater safety factors, 2.60 under static loading and 1.79 under earthquake <br /> loads. The proposed setback of 50 feet from the gas line easement is satisfactory. <br /> An updated Slope Stability Case Location Map is attached showing the locations of all <br /> stability analyses cross sections. The revised Case 3 and Case 4 Galena cross-section <br /> and results output are also attached for your reference. <br /> 13. On page 2 of the report the Operator states, the slope of the silt pond was also modeled at <br /> 3H:1 V. On page 2 of the technical revision request the Operator states the silt ponds (Phases 1 <br /> and 3) will be mined at a 2HAV slope. Please explain this discrepancy and update the stability <br /> analysis accordingly. <br /> Response: See above response to #12. <br /> 14. The operator supplied the XSTABL slope stability analysis data electronically on May 26, 2021. <br /> However, the Division was unable to open the files. Please provide the XSTABL slope stability <br /> analysis data from the Civil Resources, LLC report in a spreadsheet format to allow the Division <br /> to duplicate the analysis with Clover Technology's Galena software for verification purposes. <br /> Response: See above response to #12. Also, the revised Case 3 and Case 4 electronic <br /> Galena files have been supplied to the Division for its use in verifying the analysis. <br /> Permit Commitments <br /> 15. During the original permit application review the Operator committed to submitting a technical <br /> revision with the design information prior to construction for the slurry wall liner for Phase 1 <br /> (proposed Phase 2). See Item #25 in the adequacy response letter for the original application <br /> V 305 Denver Avenue-Suite D•Fort Lupton CO 80621 •Ph: 303-857-6222•Fax: 303-857-6224 <br />