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COLORADO <br /> ® C 0 Division of Reclamation, <br /> mil. Mining and Safety <br /> Department of Natural Resources <br /> Date: October 7,2020 <br /> To: Tabetha Lynch <br /> CC: Jason Musick <br /> From: Zach Trujillo <br /> RE: Foidel Creek Mine,DRMS File No. C-1982-056 <br /> Foidel Creek Mine TR-94 Adequacy Review Memo <br /> Tabetha, <br /> As requested I have reviewed Foidel Creek Mine's(Foidel)TR-94. TR-94 proposes to update the Foidel <br /> PAP to include modifications to the Coal Refuse Disposal Area(CRDA)due to surveying errors with the <br /> construction of the second lift. Included with TR-94 is an associated geotechnical slope stability analysis <br /> with the modified CRDA design.North West Colorado Consultants,Inc. (NWCC),on behalf of Foidel, <br /> ran a two dimensional slope stability analysis for both the completed CRDA fill slopes and global <br /> stability of the completed CRDA fill slopes and existing reclaim spoils utilizing the Morgenstern-Price <br /> method. This method is suitable for circular failure surfaces. The factor of safety results of the stability <br /> analyses are 2.3 and 2.2 respectively. These results exceed the minimum requirements for factor of safety <br /> (1.5)as required by 4.10 and subsequently 4.09.1(7). <br /> When reviewing NWCC's geotechnical analysis,NWCC states that, "[a]s noted in NWCC's original <br /> report,conservative soil properties were used in our analysis."After searching through documents in our <br /> system, I was unable to find this referenced original report.Additionally,when reviewing currently <br /> approved geotechnical reports,a range of soil properties were used previously. With that said,I am <br /> unable to determine what soil properties were used in NWCC's geotechnical analysis provided with <br /> Foidel TR-94.Additionally,there is no indication regarding where the cross-sections are located at for the <br /> CRDA with the associated geotechnical analyses.Please have Foidel provide responses to the following <br /> comments: <br /> • Please provide the soil properties used in the geotechnical analysis used for the proposed <br /> modified CRDA. <br /> • Please provide information that shows where the profiles used in NWCC's geotechnical analysis <br /> are located for the proposed modified CRDA. <br /> This concludes my review of Foidel's TR-94. If you have any questions,feel free to contact me. <br /> Sincerely, <br /> Foidel Creek Mine TR-94 Memo October 7,2020 <br /> pF COlO <br /> H <br /> 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us I * * <br /> Jared S. Polis, Governor I Dan Gibbs, Executive Director I Virginia Brannon, Director * * <br />