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u <br />The number of storage years (Y) was increased in the sedimentology sub-routine <br />until the effluent settleable solids concentratiort in the pond fliacharge exceeded <br />the water quality criterion (0.5 milliliters per liter [ml/1]), or until there was <br />two feet of elevation between the top of the sediment storage level and the invert <br />of the principal spillway. The storage year value was then set at the year <br />preceding the year that the settleable solids concentration exceeded the effluent <br />limitation or for the last year the model indicated there was sufficient storage <br />for the sediment yield from the design storm. The SEDCAD4 model results presented <br />herewith reflect a (Y) value that allows for the maximum sediment storage that is <br />either just below the elevation which would result in a settleable solids <br />concentration in the pond discharge greater than the water quality criterion or at <br />an elevation which retains sufficient capacity to store sediment yield from the <br />design storm event. <br />Pond 008 Summary <br />Total pond storage capacity (at principal spillway elevation) _ <br />Principal spillway invert elevation (ft msl) _ <br />. Storm predicted peak settleable concentration = <br />Predicted annual sediment loading = <br />Predicted sediment storage = <br />Predicted sediment storage elevation (ft msl) <br />Number of storage years (Y) _ <br />Certification Statement <br />7,66 ac-ft <br />7,015.3 ft <br />0,0 ml/1 <br />0,01 ac-ft <br />3,89 ac-ft <br />7,013.3 ft <br />270 years <br />The earthen impoundment, principal spillway and emergency spillway are pre- <br />existing. The original design, as-built plans and modifications were <br />prepared under the supervision of others. Pond 006 was originally <br />constructed as shown on Exhibit 7-17A, Sediment Pond 008 As-Built, which was <br />certified by Ronald J. Gehrke, a registered professional engineer in the <br />State of Colorado experienced in the design and construction of earthen <br />structures. The trapezoidal emergency spillway was constructed in 1992 as <br />shown on Exhibit 7-17C, Sediment Pond 008 As-Built, and which was certified <br />by Mike Alltavia, a registered profession engineer in the State of Colorado <br />experienced in the design and construction of earthen structures. The design <br />and construction o£ the replacement principal spillway, an 8-inch plastic <br /> corrugated straight pipe, approved under TR-37 in October 2005, was <br /> TR-92 5 Revised 09/07 <br />