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, <br /> . � �� . <br /> �Bonestroo <br /> Memorandum <br /> 2335 Highway 36 W <br /> St.Paul,MN 55113 <br /> � TO: DARRENAMUNDSEN PRO)ECT: DATE: E-1-2010 Te1651-63Cr4600 <br /> Fax 651-636-1311 , <br /> FROM: PHILLIP ELKIN, PE CLIENT: CITY OF ORONO www.bonestroo.com <br /> Fi�No: 139-10000-1 <br /> ' RE: WOODHILL SENIOR COTTAGES <br /> 10-3471 <br /> After reviewing the plans and drainage calculations submitted from Plow Engineering, <br /> , Inc. dated May 19, 2010 I would ofFer the following comments: <br /> Wetlands <br /> The plan show discharges to wetlands which have not previously been inventoried by the <br /> City. A wetland delineation and MnRAM analysis will need to be conducted on this , <br /> wetland to determine the applicable, setbacks, buffers and water quality requirements of <br /> the discharge. <br /> The proposed retaining wall shown along the southeast edge of the project is ten feet tall <br /> and located within the wetland bufFer. Construction of this wall will most likely result in <br /> impacts to the wetland bufFer and possibly the wetland itself. These impacts must be <br /> included in the wetland permit with mitigation measures. � <br /> Storm Sewer System � <br /> CB 2 seems unnecessary. If erosion is a concern, a reinforced open channel swale would <br /> allow more capacity and reduce the velocities which would occur in a pipe discharge. <br /> • The storm sewer basins do not identify EOF routes or provide skimming devices as <br /> required by the SWMP. <br /> Closed conduit velocities should be limited to 12fps. Outlet pipes from ponds 4 and 2 <br /> have slopes exceeding 30% and will praduce velocities in excess of 20 fps. <br /> The plans should include details of each infiltration basin's outiets—not just basin 1. <br /> Drain tile pipe used in the infiltration basins should be either PVC or HDPE dual wall <br /> smooth interior pipe. The HydroCAD model identifies drain tile pipe with corrugated <br /> interior. Single walled pipe has an inferior structural strength and corrugations which will <br /> fill with sediments and require more maintenance. <br /> Water Quality <br /> The city of Orono's Surtace Water Management Plan (SWMP) outlines water quality <br /> requirements based on the receiving water body. It is unclear what level of TSS and <br /> nutrient removal will be achieved by the infiltration basins. The applicant"wili first need <br /> to pertorm a MnRAM analysis on the receiving wetland to determine the water quality <br /> requirements. <br /> � . . <br /> Page 1 of 1 <br />