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New water and recycle water is contained here for milling operations. It shall be noted that on the west end a very <br />gradual "ramp" was incorporated into the pond so that any errant critters could safely escape. The surface of the <br />textured I-IDPE is rather rough and not slippery when wet. <br />Tailings Impoundment Area <br />Stormwater/Sedimentation Collection Pond - This structure is designed to collect stormwater runoff from the <br />Tailings Impoundment Affected Area and allow any carried sediment a chance to settle for future removal. A rip- <br />rapped discharge weir (12' long x 2' deep) is more than capable of passing tills peak flow. Sizing has been done to <br />allow for containment and settling of a 10 year/ 24-hour storm event (Peak Discharge = +/- 41.0 cfs) and controlled <br />passage of a 100 year/ 24-hour storm event (Peak Discharge= +/- 96.2 cfs). Refer to Exhibit Drawing E13 for <br />construction details and specifications. <br />A storage volume of 0.566 acre-ft (184,430 gal.) is provided for containment below the weir to give sufficient time <br />for settling any sediment. <br />This catchment and settling basin will be constructed down gradient of the disposal cell to intercept and settle <br />sediment from surface water run-off in the event of such an occurrence. Leachate shall be collected and returned by <br />pumping to the impoundment and/or water storage above the mill. Impacts to surface water will be controlled as per <br />the stormwater management plan (6.3.3(2)(c) and Exhibit T) and design details found in the Tailings Impoundment <br />Design Drawings (Exhibit E). <br />This structure also provides for a secondary containment "trap" of sorts so that if there is an unlikely Tailings <br />Impoundment failure, most, if not all, of the failed tailings will become contained here within our property <br />boundary. <br />Concrete Leachate Collection Barrier - A system consisting of a concrete barrier constructed, grouted, and pinned to <br />bed-rock down gradient of the impoundment, including a process water return and recycle pump, will be used to <br />collect and recycle leachate (see drawings of Exhibit E). Additionally it is worth note that the leachate water quality <br />exceeds that of the groundwater as demonstrated in 6.3.3(1)(i). <br />A composite liner is mechanically connected to the concrete barrier's continuous footing. This will allow for <br />leachate to migrate through the GeoComposite layer to the BDPE layer and be collected in the leachate recycle <br />system. <br />Diversion Ditch -A trapezoidal channel with a bottom width of 6 feet, side slope of 1:1 and a minimum clear depth <br />of 2 feet will be constructed at each end of the impoundment bench as it is raised, at the intersection with the natural <br />grade, to provide a permanent stormwater control. Type L riprap, sized nominally with a median diameter of D50=9 <br />inches, shall be hand placed at a depth of 18 inches. Rubble and/or slightly weathered stone sorted on-site from <br />available material that meets this size specification shall be acceptable for use. <br />This perimeter ditch will be constructed in phases as the impoundment expands. Refer to Exhibit E Drawing E7 for <br />the Phase 1 ditch and Drawing E10 for Phase 2 ditch. Interim diversion along the projected side slope line, prior to <br />raising an impoundment bench, shall be achieved by utilizing woven polypropylene sand bags (nominally 14"x26" <br />50# capacity) stacked two bags wide as the first course and one bag wide, centered, as the second course. The <br />sandbags shall be removed as permanent riprapped channel is installed. Refer to Exhibit E Drawing E13 for <br />construction details. <br />The existence of a natural diversion channel will also be acceptable for stormwater diversion as is found near the <br />bottom half of the impoundment area. This natural channel is incorporated into the sedimentation pond. This <br />system is capable of passing a 100 year/ 24-hour storm event (3.8" as reported by NOAA Atlas 2, Vol. 111) For <br />more information on stormwater management refer to 6.3.3(2)(c) and Exhibit T. <br />Impoundment -The lined impoundment, more thoroughly described in 6.33(2), will be built up using an upstream <br />method on the down-slope face from the coarser fraction of the waste stream by hydraulic placement and hydraulic <br />classification. A maximum of 40 square feet of new impoundment face will be formed daily. A maximum slope of <br />1.5h: Iv (f 33.7°) will be maintained at the face. This is sufficient to provide a stable impoundment embankment <br />Page 4 of 37