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2. Surface Water <br /> Surface water flows drain naturally from the south to the north towards the Eagle River. During <br /> mining, runoff that occurs within the disturbed area will all be routed to the active mining pit. A <br /> natural berm will be maintained along the north side of the site at all times to prevent surface <br /> water discharge. Two sumps will be installed within the site to collect stormwater and allow it to <br /> evaporate.No sediment will be allowed to leave the site and cloud any downstream waters. The <br /> site will not affect existing water rights, as the pit will not expose groundwater and will not store <br /> stormwater for more than 72 hours. After reclamation, stormwater encountered in the mining <br /> area will continue to infiltrate or evaporate via the sumps. <br /> Stormwater will runoff from the general area of the airport south of the Tower Pit, in addition to <br /> the area of the pit itself, and be collected in sumps located in the east and west ends of the site. <br /> Map C-2 shows the location of the sumps in each phase. The drainage basins are shown on Map <br /> C-1. The entire site will be enclosed by at least a 2-foot tall natural stormwater berm at all times. <br /> During mining this berm will be at least six feet tall. Following the completion of mining and <br /> reclamation, it may be reduced in height as it will no longer be needed as a visual barrier. The <br /> site access will have this berm as a hump in the access road. The rest of the site will have it as a <br /> portion of the natural visual berm. It will remain following all reclamation, as the floor of the pit <br /> is not being revegetated. <br /> Based on using an encompassing site berm,the worst case stormwater scenario to evaluate is at <br /> the end of mining. This is when the greatest drainage area for the site exists. Using the Natural <br /> Resource Conservation Service T-55 Method, the runoff for the 100-YR 24-HR event was <br /> calculated for each sump. This is then compared to the total capacity of that portion of the site to <br /> a depth of two feet to determine if there is sufficient storage capacity. <br /> Tower Pit 11L.-la• 1-and 151[M-l-1 <br /> I,1< <br /> October 2018 G-2 <br />