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Peab 0 <br />1111 ENERGY <br />Twentymile Coal, LLC <br />Mr. Jared Ebert, Environmental Protection Specialist <br />Division of Reclamation, Mining, and Safety <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />(303) 866-3567 X 8120 <br />29515 Routt County Road 27 <br />Oak Creek, CO 80467 <br />970 879 3800 <br />July 19, 2016 <br />RF: Twentymile Coal, LLC - Foidel Creek Mine (Permit No. C-82-056), Technical Revision (TR16-84) — <br />6MN Passive Water Treatment System <br />Dear Mr. Ebert: <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 (TORT) <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. <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 under round 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 TORT 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 to be discharged is expected to have iron, sulfate, and TDS levels which are above <br />natural ambient runoff. While some of the pumped ground water may be diverted for mine uses, it is <br />anticipated that most of the pumped mine water will need to be treated to meet applicable CDPS effluent <br />discharge limitations prior to discharge to Fish Creek. Based on previous studies and results from <br />operating wetlands, previous experience with passive treatment where mine discharge water was routed <br />through a wetland prior to discharge, and a subsequent site feasibility study by CH2M Hill reviewing <br />potential treatment options, the preferred treatment approach is passive treatment. <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 anerobic zones. Treatment mechanisms include <br />precipitation of iron (iron hydroxides and oxyhydroxides) and certain other constituents in oxygenated <br />open -water (aerobic) environments and complexing as sulfide compounds under anerobic conditions; <br />conversion of sulfates to insoluble sulfides under anerobic conditions, and sorption of many of the <br />constituents of TDS to organic and metal surfaces and biological reduction of anions in an anerobic <br />environment. Anerobic conditions will be established in the treatment cells through establishment of an <br />