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• This is a steady state model and should be representative of the more constant <br /> flows that will result from snowmelt runoff. Figure 3a in Appendix E shows the <br /> results of the modeling. <br /> The expected removal efficiency using the existing trap is about 58 percent. This <br /> trap was originally designed for 50 percent efficiency. The effect of enlarging this <br /> trap to promote better settling is shown in Figure 3a (Appendix E). The increase <br /> in removal effectiveness would increase to about 78 percent by doubling the size <br /> of the trap. However, reconfiguration of this trap may not be necessary. <br /> Henderson may evaluate the performance of the existing trap by sampling <br /> influent and effluent for total suspended solids (TSS) during peak discharge to <br /> quantify the evaluation. If the results of sampling indicate poor settling <br /> performance, the pond will be enlarged. <br /> The volume of the trap was checked against the criteria specified by the Urban <br /> • Drainage and Flood Control for the metro Denver area. Approximately 31.4 <br /> percent of the total basin are considered impervious (including roofs, pavement, <br /> and the final cover for Pond 1.2). Based on this ratio, the total volume of a "dry" <br /> pond is 4065 cubic feet for best management, water quality improvement. The <br /> actual volume of the existing trap is about 4620 cubic feet, indicating that the <br /> existing trap meets the Urban Drainage criteria. The Urban Drainage criteria <br /> also recommend a reservation of 20 percent for accumulated sediment. The <br /> existing trap has 13 percent additional volume for sediment. Therefore, the <br /> amount of sediment will be monitored and removed when total depth of the trap <br /> to the outlet is less than 2 feet. <br /> 2.4 Final Cover and Surface Reclamation <br /> MA ft,• <br /> 13 <br /> June 29,1999 <br /> TA.dw <br />