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Peabod <br />1111 ENERGY <br />Twentymile Coal, LLC <br />RECEIVED <br />SEP 0 7 NIB <br />Ms. Tabetha Lynch, Environmental Protection Specialion of Redamation, <br />p <br />Division of Reclamation, Mining, and Safety sMining & Safety <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />(303) 866-3567 X 8147 <br />29515 Routt County Road 27 <br />Oak Creek, CO 80467 <br />970.879.3800 <br />September 5, 2018 <br />RE: Twentymile Coal, LLC - Foidel Creek Mine (Permit No. C-82-056), Technical Revision <br />(TR16-84) — 6MN Passive Water Treatment System (Revised Submittal) <br />Dear Ms. Lynch: <br />Twentymile Coal, LLC (TC) requests CDRMS approval of a Technical Revision to our existing approved <br />Permit for construction, operation, maintenance, and reclamation of a passive water treatment system to <br />treat excess mine water discharge from the 5 -Main North (5MN) Borehole and 10 -Right (IORT) <br />Boreholes. Generally, the excess mine water discharge will be water resulting from progressive <br />dewatering of mine water accumulations in the sealed and abandoned Wadge Seam mine workings in the <br />Eastern and Northern Mining Districts. This revised submittal reflects modification of the design and <br />permitting information originally submitted in 2016, for an alternate location which avoids potential U.S. <br />Army Corps of Engineers (USACE) jurisdictional and permitting issues. <br />As TC proceeds with planned and permitted development and mining of the Wolf Creek Reserve, it will <br />be necessary to drain accumulated ground water from two underground pools which currently exist in the <br />overlying workings, as an operational and safety consideration and to comply with applicable Mine Safety <br />and Health Administration (MSHA) requirements. The north pool will be drained through an <br />underground borehole(s) and pump/piping system to the existing 5MN Borehole. The south pool will be <br />drained by the existing IORT Mine Dewatering Boreholes and transferred through existing or new <br />pipelines to either the 18 -Left Shaft site or the 6 -Main North (6MN) water handling system. Dependent <br />on the volume that must be drained from the south pool, some of this water may be transferred to 18 -Left, <br />with no treatment necessary. The deep well pumps would operate at 600 to700 gpm, but would operate <br />intermittently, with an average pumping rate of approximately 200 gpm. <br />The ground water discharge from the Mine is expected to have iron, sulfate, and TDS levels which are <br />above natural ambient runoff. While some of the pumped ground water may be directly diverted for mine <br />uses, it is anticipated that most of the pumped mine water will need to be treated to meet applicable CDPS <br />effluent discharge limitations before being discharged to the mine water system. Based on previous <br />studies and results from operating wetlands, previous experience with passive treatment where mine <br />discharge water was routed through a wetland prior to discharge, and a subsequent site feasibility study by <br />CH2M Hill reviewing potential treatment options, the preferred treatment approach is passive treatment. <br />At some future point in time after the passive treatment system is well-established, its effectiveness is <br />proven, and conditional on receipt of a Water Quality Control Division Discharge Permit, modifications <br />to the system may be permitted and implemented to allow direct discharge to area drainages. <br />The proposed passive treatment approach will consist of a series of four constructed treatment cells, <br />which will include both open water pond areas and shallow constructed wetlands to provide physical, <br />chemical, and biologic treatment in both aerobic and anaerobic zones. The initial cell will include a <br />