3.0. SR 12-13-1993 - Laserfiche WebLink

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1 . i I 1 . 1 i ~ 13. Re-analyze the proposed access at the most northerly end of the site for safety concerns and environmental concerns, specifically the need to cut down mature trees to provide adequate site lines and detennine whether or not it is reasonable to allow an access off of Jackson at this point. At the City Council workshop meeting on November 22, 1993, the developer indicated this access point would be removed. Therefore, no analysis of this area was performed. B. DRAINAGE " 152-090I.d~~ 1. Re-analyze the drainage plan, specifically the two-thirds of the site that flows to the east under TH 169. Analyze the need or lack thereof for an outlet from the regional pond, given the phasing of the proposed shopping center. Under the proposed plan to drain water to the east, as shown on Exhibit 8, approximately two~thirds of the Elk Park Center site drains to ponds that ultimately outlet under TH 169 to Wetland 171W (171W is the DNR Protected Waters designation). The remaining third of the site drains to two ponds along the south edge of the property. From the two south ponds the water drains into the City storm sewer system along Freeport A venue, ultimately flowing through the City and into the Mississippi River. If this option of drainage to the wetland is implemented, an outlet from the wetland is necessary to meet the approval of the Minnesota Department of Natural Resources and other agencies. A feasibility study completed in October 1993 concluded that, during a 100-year storm event, stormwater from the Elk Park Center development would raise the water surface of Wetland 171 W relatively higher than the current rise in the wetland for a 100-year event. The Minnesota DNR requires an outlet be provided for DNR Protected Waters that will maintain water fluctuations from storm water discharges consistent with existing conditions. A model of the existing conditions shows water levels rise 2.81 feet for a 100-year event, whereas with Elk Park Center draining to the wetland with no outlet, the rise if 5.60 feet. . The same feasibility report from October 1993 concluded that a 48" outlet would be sufficient to maintain water fluctuations consistent with existing conditions. This 48" storm sewer pipe would run along the eastern right~of- way of TH 169 from the wetland southerly to near the railroad tracks that cross TH 169. Construction of the 48" outlet from Wetland 171W would not need to occur until the final phases of the Elk Park Center development. During the first phases of construction, if the project is phased properly, stormwater could be ponded on the remaining undeveloped site following Best Management Practices without providing an outlet across TH 169 to the wetland. -9- 230-152-10