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prior to raising an impoundment bench, shall be achieved by utilizing woven polypropylene sand bags <br />(nominally 14"x26" 50# capacity) stacked two bags wide as the first course and one bag wide, centered, as the <br />second course. The sandbags shall be removed as permanent riprapped charmel is installed. Refer to Exhibit E <br />Drawing E13 for construction details. <br />The existence of a natural diversion channel will also be acceptable for stormwater diversion as is found near <br />the bottom half of the impoundment area. This natural channel is incorporated into the sedimentation pond. <br />This system is capable of passing a 100 year/ 24-hour storm event (3.8" as reported by NOAA Atlas 2, Vol. 111). <br />The Tailings Impoundment shall also be constructed to maintain a minimum of one (1) foot of freeboard between <br />the ponded area of process water collection and the rising embankment face. This will be sufficient to contain a 100 <br />year/24-hour event that falls inside the Diversion Ditch perimeter. A significant level of safety above and beyond <br />the containment requirement of a 10 year/24-hour event. Refer to Exhibit B for a description of the Temporary <br />Substitution Water Plan to account for capturing any of this rainfall in the lined area of the impoundment. <br />Also during a 100 year/24-hour event, a Peak Discharge into the Sedimentation Collection Pond will be produced in <br />the amount of +/- 96.3 cfs. <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 <br />rip-rapped discharge weir (12' long x 2' deep) is more than capable of passing this peak flow. Sizing leas been <br />done to allow for containment and settling of a 10 year/ 24-hour storm event (Peak Discharge = +/- 41.0 cfs) <br />and controlled passage of a :100 year/ 24-hour storm event (Peak Discharge = +/- 96.2 cfs). Refer to Exlubit <br />Drawing E13 for 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 <br />time 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 <br />retuned by pumping to the impoundment and/or water storage above the mill. Impacts to surface water will be <br />controlled as per the stormwater management plan (Exhibit T) and design details can be found in the Tailings <br />Impoundment Design Drawings (Exhibit E). <br />Page 32 of 37