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A sensitivity analysis evaluated the number of storage years (Y) to maximize <br />sediment storage capacity and maintain compliance with the applicable rules <br />and regulations. The number o£ storage years (Y) was increased in the • <br />sedimentology sub-routine until the effluent settleable solids concentration <br />in Pond 10 discharge exceeded the water quality criterion (0 .5 milliliters <br />per liter [ml/1]), or the model indicated there was less than one {1) foot of <br />storage room in the pond (the elevation difference between calculated top o£ <br />sediment storage and principal spillway invert elevation). The storage years <br />(Y) value was then set at the year proceeding the year the settleable solids <br />concentration exceeded the effluent limitation or for the last year the model <br />indicated there was sufficient storage for the design storm sediment yield. <br />The SEDCAD4 model results present the maximum sediment storage while <br />retaining capacity to store the design storm runoff and maintain compliance <br />with applicable rules and regulations. <br />Storaqe Capacity. Results of the TR-30 SEDCAD4 demonstration show the storm <br />runoff volume from the 10-year, 29-hour event to be 2.17 acre-feet (ac-f t). <br />There will be no discharge through the emergency spillway during the 10-year, <br />29-hour event. In addition, there will be adequate freeboard between the <br />water surface elevation and top of embankment for both the 25-year and 100- <br />year, 29-hour events. The following summarizes storage capacity for the TR- <br />30 10-year, 24-hour event SEDCAD4 demonstration. <br />Total pond storage capacity (at dewatering orifice elev <br />Principal spillway invert elevation (ft msl) _ <br />Storm predicted effluent peak settleable concentration <br />Predicted annual sediment loading = <br />Predicted sediment storage = <br />Predicted maximum sediment storage elevation (ft msl) _ <br />Number of storage years (Y) _ <br />9.37 ac-ft <br />6,784.0 ft <br />0.0 ml/1 <br />0.09 ac-ft <br />7.10 ac-ft <br />6,783.0 ft <br />80 years <br />The 25-year and 100-year, 24-hour storm event SEDCAD demonstrations present <br />conservative top of sediment elevations. Because these demonstrations assume <br />the principal spillways are clogged, the sediment storage elevations are over <br />estimated. While the calculated sediment storage elevations for the 25-year <br />and 100-year events are above the principal spillway invert elevation (6-inch <br />de-watering orifice), the respective sediment storage elevations are less <br />than the top of the 36-inch CMP riser portion of the principal spillway. <br />Spillways. In accordance with Rule 4.05.9(2), Pond 010 was designed and <br />constructed with both a principal and emergency spillway. Exhibit 13-4A <br />shows spillway locations and specifications. The principal spillway consists <br />of a 6-inch diameter dewatering orifice cut into a 36-inch CMP riser which <br />drops into the 29-inch CMP barrel. This spillway will keep the pond level at <br />the 6,784.0 elevation. The SEDCAD4 demonstration in Addendum 13-3A-A shows, . <br />in accordance with Rule 4.05.9 (2)(b), there is no discharge through the <br />emergency spillway during the 10-year, 24-hour event. The peak stage <br />elevation from the 10-year, 24-hour event is shown on Exhibit 13-4A. <br />TR-30 13-3A.9 Revised 05/07 <br />