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1 <br />5.0 STORMWATER RUNOFF CONTAINI\1ENT <br />' An analysis was conducted of the runoff expected from a 100-year, 24-hour storm within the area <br />tributary to the tailings impoundment. This tributary area will include the aggregate of: <br />' The footprint of the interior of the tailings impoundment; <br />The area upstream of the impoundment, but below the interceptor/diversion ditch; and <br />• The ore stockpile area, from which potentially contaminated runoff will be pumped to the tailings <br />' impoundment. <br />Based upon information obtained from National Oceanographic and Atmospheric Agency (NOAA) <br />' maps, the maximum rainfall to be expected from a 100-year, 24-hour storm in the vicinity of the site is 4.6 <br />inches. The aggregate area tributary to the tailings impoundment is approximately 1.91 acres (83,290 ftr). <br />' Therefore, the maximum accumulated runoff from the tributary area is expected to be 0.73 ac.ft (31,890 ft') <br />(1.91ac. x 4.6"/12"). The surface area of the impoundment at the maximum design elevation of impounded <br />tailings (8,418 ft. AMSL) is approximately 26, 825 ft'. Therefore, the incremental depth of water from a <br />100-year, 24-hour storm would be approximately 1.19 ft. Two feet of freeboard will be provided within the <br />expanded impoundment. Therefore, the freeboard allowance is adequate to accommodate the design storm. <br /> <br /> <br />1 <br /> <br />1 <br /> <br />1 <br />1 <br />1 <br /> <br />14 <br />