Laserfiche WebLink
BOLTON 2638 Shadow Lane <br /> f'\ Suite 200 <br /> & MENK <br /> Chaska, MN 55318-1172 <br /> Real People. Real Solutions. Ph: (952)448-8838 <br /> Fax: (952)448-8805 <br /> Bolton-Menk.com <br /> March 1, 2021 <br /> City of Orono <br /> Attn: Jeremy Barnhart <br /> 2750 Kelley Parkway <br /> Orono,MN 55356 <br /> RE: Preliminary Plat Application <br /> Long Bridge <br /> Engineering Review#1 <br /> Dear Jeremy: <br /> As requested,I have completed an engineering review of the revised documents submitted for the above <br /> referenced project. We offer the following observations,comments,and recommendations for your <br /> consideration: <br /> 1. Four dry retention basins are proposed for stormwater runoff management to meet regulatory <br /> requirements. The following must be considered regarding stormwater management: <br /> a. Per City requirements,the proposed stormwater management system must limit proposed <br /> peak runoff rates to that of existing for the 1, 10,and 100 year—24h hour events. Per <br /> NPDES requirements,the system must also treat the water quality volume,calculated as 1" <br /> times the sum of new and fully reconstructed impervious surface.If infiltration is <br /> prohibited as outlined by NPDES requirements,a wet sedimentation basin or filtration <br /> basin may be utilized. <br /> b. Based on suspected soil conditions and the submitted calculations,site soils do not seem <br /> conducive for infiltration. If infiltration is not possible due to site soils,volume control will <br /> not be required per NPDES requirements,but the water quality volume must still be <br /> treated.A permanent volume must be provided below the outlets for each basin to treat this <br /> volume. If using filtration,an underdrain must be installed with the basins to ensure <br /> complete drawdown between rainfall events. In addition,filtration basins should be located <br /> a minimum 3' above the water table to ensure proper functionality. <br /> c. Per City requirements to track TMDLs and reduce loads to meet required Waste Load <br /> Allocations,the calculations for Total Suspended Solids(TSS)and Total Phosphorus(TP) <br /> loading must be provided. <br /> d. Facilities necessary for the ultimate development(street construction, sewer,basins,etc.) <br /> must be installed and the site mass-graded at the same time as street construction to ensure <br /> all drainage ways,watersheds,and runoff management systems are constructed per the <br /> approved Stormwater Management Plan and are sized adequately for proposed <br /> improvements. <br /> e. An 8' wide bench must be provided around each basin to provide access to the outlet and <br /> for basin maintenance. <br /> f. Basins must be permanently vegetated prior to issuance of any building permits. <br /> g. Native vegetation should be utilized in basins and wetland buffers. <br /> B:\ORNO\Surface Water Management\MS4 Administration\MCM-5_Post-Construction Stormwater Management\2_Site Plan Reviews\Long Bridge\Long <br /> Bridge_PrePlatReview 2021-03-01.docx <br /> Bolton&Menk is an equal opportunity employer. <br />