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The watershed area for Pond 004 is presented on Map 2.05.3 M4, Drainage and Sediment Control <br />Plan. The structure elevations input into the model are based on the physical survey conducted in <br />September 2005. The stage /storage inputs utilized data presented by SCC in the as -built report <br />previously approved as part of Seneca H Mine Technical Revision No. 37 (TR -37). This TR was <br />approved by CDRMS on September 12, 2007. <br />• <br />U <br />SEDCAD4 uses an Annual R factor for a set number of storage years (Y) to determine if the pond <br />capacity is adequate to store the calculated sediment yield from the design storm. The 2009 <br />sedimentology demonstration used an Annual R factor of 10, which is appropriate for reclaimed and <br />revegetated landscapes. In previous Pond 004 SEDCAD4 modeling exercises (i.e., the TR -37 <br />demonstration) the storage year value (Y) was artificially set at two (2) years. Use of this value <br />resulted in low sediment storage capacity because the model suggested that the pond needed a large <br />amount of capacity to store water. <br />The number of storage years (Y) was increased in the sedimentology sub - routine until the effluent <br />settleable solids concentration in the pond discharge exceeded the water quality criterion (0.5 <br />milliliters per liter [ml/1]), or until there was two feet of elevation between the top of the sediment <br />storage and the invert elevation of the principal spillway (in accordance with guidance in the <br />SEDCAD4 User's Guide [Warner et al, 1998]). The storage year value was then set at the year <br />preceding the year that the settleable solids concentration exceeded the effluent limitation or for the <br />last year the model indicated there was sufficient storage for the sediment yield from the design storm. <br />The SEDCAD4 model results presented herewith reflect a (Y) value that allows for the maximum <br />sediment storage that is 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 an elevation which <br />retains sufficient capacity to store sediment yield from the design storm event. <br />The 2009 SEDCAD4 demonstration shows that with the revised number of storage years (650 years), <br />the effluent from Pond 004 meets the requirements of Rule 4.05.2(7). In addition, the updated <br />SEDCAD4 demonstrations shows that the pond satisfies the operational criteria of Rule 4.05.9(2)(b) <br />and Rule 4.05.9(2)(c)(iii). <br />Pond 004 As -Built Summary <br />Total pond storage capacity (at principal spillway elevation) _ <br />Principal spillway invert elevation (ft msl) = <br />Storm predicted peak settleable concentration (outflow) _ <br />Predicted annual sediment loading = <br />Predicted sediment storage (total volume) _ <br />Predicted sediment storage elevation (ft msl) _ <br />Number of storage years (Y) = <br />7.56 ac -ft <br />6,948.2 ft <br />0.0 ml/l <br />0.01 ac -ft <br />4.0 ac -ft <br />6,946.2 ft <br />650 years <br />2.05.3 -E2.C5 11/09 <br />