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•fi' � <br /> Memorandum �Bonestroo <br /> To: Tom Kellogg Project: 1200 Old Chrystal Bay Road Date: 6/2�/ZOO� 2335Highway36 W � <br /> St.Paul,MN 55113 <br /> From: Lance Hoff Cllent: �It�l Of OfOf10 Tel 651-636-4600 <br /> � Fax 651-636-1311 <br /> Re: Drainage Review File No: 139 Gen-Plat 3181 www.bonestroo.com <br /> As request,we have reviewed the proposed project against the requirements and standards of <br /> the City of Orono. Our comments follow below: <br /> 1. An emergency overflow(EOF)must be provided from the pond. The EOF elevation <br /> should be placed at the calculated 100-yr HWL of 950.6. The EOF must be armored � <br /> with either riprap(could be granite)or permanent erosion control mat(which can be <br /> vegetated). <br /> 2. Pond contours should be provided below the NWL. <br /> 3. A 10'wide 10:1 aquatidsafety bench is required between the elevations of 950(NWL) <br /> and 949. <br /> 4. Existing conditions peak flow rates are not met. The table below summarizes our <br /> modeling results: <br /> Storm Retum <br /> Period <br /> Peak Flow 2-Y� 10-yr 100-yr . <br /> (cfs) . <br /> West Existing 0.5 1.8 4.0 <br /> Proposed 1.4 3.3 6.2 <br /> East Existing 0.3 1.4 3.1 <br /> ' Proposed'� 0 0.2 0.6 <br /> Overall Existing 0.8 3.2 � 7.1 <br /> Proposed 1.4 3.3 6.4 <br /> *Includes the effects of the proposed pond. � <br /> The effects of the pond are sufficient to meet existing conditions to the east. <br /> � However, none of the:existing conditions peak flow rates to the west are met and the <br /> overall existing conditions are only met for the 100-yr storm. Modifications are <br /> : required to the drainage systerrrto reduce peak flows to the west and/or route flows <br /> : from the west to the proposed pond. <br /> 5. 'Similar to the water quantity analysis,water qual'ity is easily met for the east side of <br /> the property due to the proposed pond. The west side has no proposed water quality <br /> � treatment. This is problematic from both a water quantity and quality perspective in <br /> � that the majority of the proposed hard cover is designed to drain to the west. <br />