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4.5 Sediment Pond Designs <br />The ponds will all be temporary structures, and therefore must be able to hold the 10 -YR, 24 -HR <br />runoff while either holding the 25 -YR or passing it safely through an emergency spillway. Maps G -2, <br />G -3, and G -4 show the pond design details, including stage- storage curves, plan views of the ponds, <br />and spillway designs. As shown in Table G -7 below, all of the ponds can contain the 10 -YR and 25- <br />YR events. For this reason, there is no flood routing demonstration of the emergency spillways, but <br />there are designs for these spillways in case a much larger event occurs. This goes beyond the design <br />requirements but has been employed regardless. <br />The ponds will each have two discharge devices: 1) a 4" pipe with a valve that is normally shut and <br />will only be opened after large storm events and 2) a trapezoidal emergency spillway built into the top <br />of the embankment. These ponds will only be present for the life of the mine. After such time, the <br />drainage areas leading to the ponds will be fully reclaimed. It is important to note that these areas are <br />now almost devoid of vegetation so that SMO will be significantly improving the long term <br />reclamation of the site and lessening the sediment contributions to Sneffels Creek. <br />Revenue Mine August 2012 G -21 <br />