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Q& MLENK <br />Real People. Real Solutions. <br />January 9, 2418 <br />City of Orono <br />Attn: Jeremy Barnhart <br />2750 Kelley Parkway <br />Orono, MN 55356 <br />RE: Preliminary Plat Application 18-3999 <br />Southways Addition <br />Engineering Review #1 <br />Dear Jeremy: <br />Resolution Exhibit C <br />635 <br />2638 Shadow Lane <br />Suite 200 <br />Chaska, MN 55318-1172 <br />Ph: [952) 448-8838 <br />Fax: (952) 448-8805 <br />Bolton-Menk.com <br />As requested, I have completed an engineering review of the documents submitted for the above <br />referenced project. In addition, Adam Edwards has provided comments for inclusion with this review. <br />We offer the following observations, comments, and recommendations for your consideration: <br />1.0 GENERAL: <br />1.1 Stormwater management for the site to meet regulatory requirements is proposed through use <br />of wet retention basins. The following should be considered regarding the proposed system: <br />a. Volume control and water quality measures must be provided as well to meet NPDES <br />requirements. Plans should be revised to include volume reduction equal to I" of runoff <br />from the new impervious surface. If infiltration is considered infeasible, other methods of <br />volume reduction must be considered. It appears that there are sufficient areas high <br />enough above the water table to provide localized filtration practices or amended soils. <br />Also, the overall estimate of Total Suspended Solids (TSS) and Total Phosphorus (TP) <br />from proposed improvements must be reduced from pre -project conditions. Calculations <br />detailing volume control and water quality compliance must be submitted for review and <br />approval. If the applicant pursues a design with less than the normally required infiltration <br />volume, sequencing of design to provide treatment to maximum extent practical must be <br />provided. <br />b. An Outlet Control Structure (OCS) that provides skimming must be installed on the wet <br />retention ponds in order to keep floatables in ponds. The following should be considered <br />regarding OCS design: <br />i. The inlet pipe from the pond to the OCS should be submerged with back slope from the <br />UCS to the pond to facilitate maintenance. The normal water level should be <br />controlled by a weir in the structure or the outlet pipe. The inlet pipe should be one <br />nominal size larger than the outlet pipe to limit flow control and turbulence at the pond <br />interface. <br />ii. A sloped rim should be utilized, per City Standard Details, with the bottom of the rim <br />placed at the predicted 100 year high water level. <br />iii. A trashguard should be installed on the outlet pipe. <br />c. Wet retention basins must provide a minimum 1800 cubic feet per acre of drainage area. <br />The stage -storage curves for permanent pools must be submitted for review to verify <br />H:+OBNO\C13115486'z-18.3999 Brackets Poitnt'\Southways_Pre PlatRevlew-1_2018-01.09Aocx <br />Ballon S Meek is an <br />