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� ,,, <br /> �Bonestroo <br /> Memorandum <br /> 2335 Highway 36 W <br /> St Paul,MN 55113 <br /> T0: DARREN AMUNDSEN PRO]ECT: 10-3460 COMMON DATE: MAY7,2010 Te1651-63Cr4600 <br /> B 0 N D Fax 651-636-1311 <br /> FROM: PHILLIP ELKIN, PE CLIENT: CITY OF ORONO www.bonestroo.com <br /> RE: STORMWATER REVIEW FILENO: 139-10001 <br /> After reviewing the plans and drainage calculations submitted from BKBM,dated April 23, <br /> 2010 I would offer the foliowing comments: <br /> General Comments <br /> • The proposed project will need to meet the water quality requirements of the <br /> Minnehaha Creek Watershed District and the NPDES construction permit. <br /> • The plan will need to include details on pipe stubs shown at the playground and <br /> upper west corner of the project. <br /> • The storm water pond calculations from the 10-day snowmelt need to be <br /> included with the modeling information. <br /> • The overFlow swale of the proposed storm water pond should be reinforced with <br /> rip rap or an equivalent material which withstand the overflow velocities of the <br /> 10-day snow melt. <br /> • Storm water ponds require outlet control structures with skimmers. The <br /> skimmers should extend below the normal water level by at least 4-inches and <br /> have a discharge velocity of 0.5 fps. <br /> • Detention ponds are required to provide an average detention time of 6 hours for <br /> the 2-inch rainfall event. These caiculations should be included in the storm <br /> water model. <br /> • The permanent pool volume of the storm water pond falls short of the City's <br /> requirement. Ponds must be designed to hold the runoff volume from a 2.5 inch <br /> rainfall event below the normal water level. <br /> • A 10-ft wide safety bench shouid be provided in accordance with the City pond <br /> sizing standards. <br /> Paqe l o!/ <br />