2016-08-11_REVISION - C1982056 (6)

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Twenty rile Coal, LLC. Page 2 August 11, 2016 the approved reclamation plan discussed in section 2.05.4 of the permit. Adequacy issues pertaining to the currently proposed reclamation plan are discussed in section 2.05.4 of this letter. 6. The "Mine Water Discharge and Recycle System" section on proposed page 2.05-50 and the "Fish Creek Dewatering Boreholes, Treatment Systems, and Transfer Pipeline" sections were recently revised with MR299. These revisions were not included in the proposed revised section. Please update these pages to include the revisions made with MR299. 7. Proposed revised page 2.05-50.10 does not appear to take into account the approval of MR299, the proposed revised text does not follow with the preceding page. Please review these pages and revise the most recently approved permit text and insure they follow the preceding and subsequent text and pagination. 8. The design information for the passive water treatment system contained in Exhibit 49EE must be certified by a qualified registered professional engineer experienced in the design and construction of impoundments per Rule 2.05.3(4)(a)(ii)(A). Please submit documentation to be included in the proposed Exhibit that these designs are certified per the cited rule. 9. The current design information for the 6MN Reservoir is contained in Exhibit 8CC of the permit. Please update this exhibit to indicate that the design of the Reservoir has been updated with TR - 84 to include a spillway to facility discharge from the passive water treatment system. Please cite where the modified design can be found in the permit. 10. The current 6MN Reservoir is designed as a closed system and the "upper diversion ditch" was designed to divert 13.16 acre-feet of runoff from a 119.09 acre area around the reservoir based on a 100 year -24 hour storm event. Now it appears a large portion of this 119.09 acre area watershed will be diverted directly into the 6MN Reservoir with the south and north diversion ditch around the proposed passive treatment system. TC submitted Exhibit 49EE-F1, Sheet 1 which also has "Exhibit EX49-172" which is a cross section of the modification of the reservoir embankment to include a new primary spillway for the 6MN Reservoir. However, TC did not provide documentation that the spillway design complies with Rule 4.05.9(2). The spillway system must be designed to safely pass the applicable design precipitation event (100 -year, 24-hour precipitation event because the Reservoir meets the size criteria outline in Rule 4.05.9(4)) plus inflow from the underground mine water. Please provide this documentation or modify the design as necessary for compliance with Rule 4.05.9(2). 11. Section 4.6 of proposed Exhibit 49EE contains a discussion of the basis for the design of the North and South Diversion Ditches. The diversions are depicted in the cross sections provided in Appendix C to Exhibit 49EE. In accordance with Rule 4.05.3(7) the diversion design shall incorporate the following: a. Channel lining, including channel riprap, shall be designed using standard engineering practices to pass safely the design velocities.