04/25/2001 Env Bd Packet - Laserfiche WebLink

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CYAN SITE GRADING AND NEW WATER QUALITY TREATMENT POND Site grading will occur to facilitate construction of the SuperTarget Store and other retail shops, construction of parking Tots, depressed islands, planting beds; one water quality treatment pond, creation of bio - swales and bio- retention basins. Existing site soil regime is of a naturally high infiltration media. The soil is classified by the Soils Conservation Service as Zimmerman fine sand and Category A soils. Drainage calculations (see Exhibit F) for the predevelopment 100 -year event computed a total site runoff of only 1.54 cfs. In order to maintain the post - development runoff rates at the predevelopment rates a storage pond with dry storage above the normal wet water level is planned on the site. Bio- retension basins are located in the northeast and southeast corners of the site. The storm water treatment pond is planned to have a. wet storage volume of 13.5 acre -ft (National Urban Runoff Program (NURP) wet volume required 5.5 acre -ft) and a dry storage capacity of 9.9 acre -ft and discharge from the site through one each 2 -inch and 6 -inch diameter pipes. The smaller 2 -inch diameter is to minimize storm water discharge for the one -year event to 0.05 cfs and the two pipes combined limit the 100 -year event to 1.21 cfs. The storage depth will bounce for each of the various rainfall frequency events with maximum depth of 5.0 feet in the 100 -year event. (See Exhibit F) Per communications with city staff and DNR Area Hydrologist, Mr. Tom Hovey APPLICANT understands that the ordinary high water (OHW) elevation of the nearest lake (George Watch Lake) to the southeast of the site is 883.5 to 884.0 and has a regional flood plain elevation of 886.9. This brings the OHW into the northern shoulder right -of -way of I -35W. APPLICANT will progress with Rice Creek Watershed District approval of the grading, drainage, and wetland impact/mitigation plan. The project will require approvals from the watershed district and city. SITE ACCESS AND TRAFFIC The site will gain access from two (2) planned locations long Lake Drive. No access to 77th Street is planned. Apollo Drive is planned to be extend easterly into the site. A secondary access point is planned along Lake Drive north of Apollo Drive. • The City is conducting traffic and roadway feasibility studies for improvements necessary due to normal growth, other developments underway, and this APPLICATION. The City as to roadway widths, lane configurations, center islands, traffic signals and right -of -way requirements has not released preliminary design considerations. APPLICANT has provided all information it City as to projected traffic volumes and will continue to support the traffic and roadway study needs. PARSONS TRANSPORTATION GROUP Barton•Asehman • De Lauw. Collier, • Steinman Town Center Narrative Page -15- 04/ 09/ 01