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A concrete trickle channel is necessary within the pond, parallel to Eighth Street <br />along the south side of the proposed berm, to transport trickle flows from the <br />existing 66" x 48" CMP culvert under Eighth Street at Maple Street. The pond <br />northerly berm has been designed to a maximum height of ten feet above Eighth <br />Street. The top of the berm would be located approximately 60 feet south of the <br />proposed south edge of Eighth Street so as to soften the appearance of the berm as <br />viewed from the north and accommodate future street widening of Eighth Street. <br />The existing 8' x 6' box culvert under Main Street would need to be extended on <br />the upstream end to accommodate the future widening of Eighth Street and <br />construction of the berm. It is anticipated that the regional detention pond will be <br />utilized for both passive recreation use and for active uses such as soccer. <br />Preliminary grading for the regional detention pond was prepared in order to <br />determine volumes and approximate earthwork quantities. The area of land <br />required to construct the pond is approximately 60 acres. <br />Volume 3 of the Urban Drainage & Flood Control District's Manual was utilized <br />for the pond water quality design component. Based on the upstream tributary <br />watershed percent impervious of 2.28 % and an extended dry detention pond drain <br />time of 40 hours, the required water quality capture volume was found to be 6.7 <br />acre-feet. To accommodate this volume, the bottom three feet (elevation 4979.5 <br />to elevation 4982.5) of the pond will function as a water quality component as <br />shown on the preliminary design drawing and its related details. By providing the <br />water quality component, the proposed regional detention pond will meet the <br />National Pollution Discharge Elimination System (NPDES) permit requirements <br />for best management practices. The NPDES permit is required to ensure that Best <br />Management Practices are used to reduce the pollutants in storm water discharges <br />associated with construction activities. <br />Preliminary Regional Detention Pond Costs: <br />A preliminary regional detention pond design and construction cost opinian was <br />prepared by Rocky Mountain Consultants, Inc. and is included on the following <br />page. Components of the cost estimate and quantities were derived from the <br />preliminary design drawing contained within Appendix 4. <br />19 <br />