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To: Jared Ebert <br /> Date: December 29. 2017 <br /> Page 16 <br /> Response 31 <br /> The projected, maximum water surface elevation in the pond is projected to occur as <br /> dewatering is initiated in Phase 1 (when groundwater storage and the natural groundwater <br /> flow rate must be captured). As dewatering commences, the rates drop resulting in a <br /> reduced standard operating surface elevation. Both conditions leave adequate freeboard <br /> in the pond to accommodate stormwater flows. See Section 5.1 in the revised <br /> groundwater modeling report. <br /> Comment 32 <br /> The "general backfill detail"provided on Exhibit F shows a perforated drain pipe set at <br /> the level of the base of the excavation on top of bedrock and fed/drained by perforated <br /> riser pipes. Please provide more detailed plans for this drain construction including, but <br /> not limited to:pipe diameter, elevations and gradients, riser spacing,filter material, geo- <br /> textile wrap used, etc. <br /> Response 32 <br /> Telesto has added an additional figure to the mine plan, and three new drawing sheets in <br /> Exhibit G that details the plan for the perimeter drain system. The drain on the south side <br /> of the Little Cache is projected to be 8" diameter while the drain on the north is 6" <br /> diameter. The drains will be installed from 0 to 0.5% overall slope. Risers are planned <br /> every 400 feet. Filter material is limited to drain sand as specified with no geo-textile <br /> wrap. <br /> Comment 33 <br /> Please provide documentation that the perforated drain as designed will function to pass <br /> groundwater around the lined pits to mimic pre pit groundwater hydraulics and will <br /> prevent offsite impacts from mounding and shadowing. <br /> Response 33 <br /> The purpose of the perforated drain system is to "replace" the natural hydraulic capacity <br /> of the aquifer that has been reduced by the lining system. The current groundwater flow <br /> parallels the Cache la Poudre River. The flow rates through the site area range from 160 <br /> (north side) to 280 (south side) gallons per minute (gpm). The corrugated and perforated <br /> pipe placed horizontally (totally flat) has the capacity to transmit 172 and 388 gpm, <br /> Response to DBMS comments T E L E S T O <br />