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C-s <br />COLORADO <br />Division of Reclamation, <br />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 <br />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 * 1876* <br />