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COLORADO <br />Division of Reclamation, <br />Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />Inter Office Memorandum <br />To: Tabetha Lynch, DRMS <br />From: Robin Reilley, GISP, DRMS <br />Date: 6 December 2018 <br />RE: Foidel Mine; C1982-056 <br />TR84 Adequacy Review <br />I received a request on 8 November 2018 to assess the above referenced permit renewal for <br />compliance with rules 4.05.3 and 4.05.9 and, their associated adequacy questions. The Adequacy <br />questions date form 11 August 2016. New design drawings for the proposed system were <br />received by DRMS on 7 November 2018 and reviewed. The documents reviewed comprised the <br />CH2M Hill report entitled: <br />1. Twentymile Coal Mine Discharge Passive Treatment System prepared in October 2018 <br />for Peabody Energy <br />2. Final Design Drawings included in Appendix C <br />3. Appendix G; Foidel Creek 6M7VMine Water Storage and Stormwater Design Basis. <br />4. Previous adequacy and responses <br />My review follows. Adequacy review questions are numbered and carry on the previous numbering system. <br />10. The current 6MN Reservoir is designed as a closed system and the "upper diversion ditch" was <br />designed to divert 13.16 acre-feet of runoff from a 119.09 acre area around the reservoir based on <br />a 100 year -24 hour storm event. Now it appears a large portion of this 119.09 acre area watershed <br />will be diverted directly into the 6MN Reservoir with the south and north diversion ditch around <br />the proposed passive treatment system. TC submitted Exhibit 49EE-F1, Sheet 1 and includes <br />Exhibit EX49-172 which is a cross section of the modification of the reservoir embankment to <br />include a new primary spillway for the 6MN Reservoir. However, TC did not provide <br />documentation that the spillway design complies with Rule 4.05.9(2). The spillway system must <br />be designed to safely pass the applicable design precipitation event (100 -year, 24-hour event), <br />because the Reservoir meets the size criteria outline in Rule 4.05.9(4)) plus inflow from the <br />underground mine water. Please provide this documentation or modify the design as necessary <br />for compliance with Rule 4.05.9(2). <br />DRMS Response 27 November 2018 <br />of COLO <br />H0 <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us I ** <br />John W. Hickenlooper, Governor I Mike King, Executive Director I Virginia Brannon, Director * 1876 <br />