2019-02-20_REVISION - M1988112 - Laserfiche WebLink

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RECEIVED Battle Mountain Resources,Inc. FEB 2 0 2019 P.O. Box 310 DMSCN OF RECIAWTIN San Luis, CO 81152-0310 MINING AND SAFETY February 12, 2019 .VIr. Lucas West State of Colorado Division of Reclamation, Mining and Safety 1313 Sherman Street, Room 215 Denver, CO 80203 Re: Addendum to TR-34 South Diversion Ditch Overflow Section Grading San Luis Mine Project Permit No. M-88-112 Dear Mr. West: The purpose of this letter is to provide notice on regrading work of the South Diversion Ditch Overflow Section for Battle Mountain Resources Inc.'s (BMRI) Permit No. M-88-112. As.previously submitted in TR-34, the Design Report, South Diversion Ditch Drop Structure (Miller Geotechnical Consultants, Inc., February 2017) details the design approach of the diversion ditch, overflow section, and drop structure. The South Diversion Ditch was designed to divert upland runoff from a 100-year event around the perimeter of the tailings storage facility (TSF) impoundment and over the south abutment of the tailings dam via a drop structure. Larger floods were intended, by design, to overtop the ditch and flow into the tailings impoundment, which has adequate capacity to contain floods up to and including the probable maximum flood (PMF) event. The portion of the ditch that is designed to overtop is called the overflow section. During the PMF, 1,800 cfs (approximately 41ac-ft) would pass over the overflow section to the TSF. In the fall of 2016, routine maintenance was performed on the South Diversion Ditch. This maintenance included removal of accumulated sediments, vegetation, and slight regrading of the Ditch in a few areas. The maintenance activities did not change the existing function of the Ditch. Part of the 2016 planned Ditch maintenance included reshaping the overflow section. This planned work included lowering the west side of the Ditch, on the east side of the tailing facility, for a length of approximately 500 feet, to an elevation of 8625.5 feet above mean sea level (amsl). Since the overflow section grading was located over a portion of the TSF liner, BMRI postponed this portion of the Ditch maintenance until the depth of the liner could be field verified.