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Preliminary Site Plan Review -Residence at The COR <br />October 28, 2010 <br />Page 6 of 9 <br />The COR Development utilizes regional stormwater ponds for rate control and water quality treatment. <br />Each individual site needs to provide additional water quality treatment through the use of rain gardens, <br />water quality treatment structures, or other BMP's. The plan is proposing to install a conventional system <br />sewer system (inlet structures and pipes) that lead to discharge points into the existing stonn sewer <br />system adjacent to the site. Drainage calculations were received but additional information is required.for <br />the appropriate sizing of the proposed Aqua -swirl structures. The AS-3 and AS-4 devices may handle the <br />water quality treatment flows; however, the outlet pipe sizes are 10"/ 12" respectively and do not match <br />the design pipe sizes of 15" and 18" shown on the storm sewer plans; the AS-7 and AS-8 devices have <br />adequate outlet sizes and will provide treatment for up to the 10 year event. Additional BMP's should <br />also. be considered and investigated to provide for some rate control and lessen the need for downstream <br />piping/structure sizing, and reduce the volume of water leaving the site. <br />Please identify overflow routes for all the "ponding areas" around catch basins; especially in area 4 <br />between the parking ramp and proposed liner building. Explain drainage patterns and overflow routes <br />should one or more of these basins become clogged and/or frozen; it appears as if only 2.5" of freeboard <br />. is proposed from the entrances on the back side of the proposed liner building. The City currently <br />experiences freezing problems with the floor drains in the parking ramp and we do not want to take <br />,_ additional drainage into our stonnwater system. A maintenance plan should be considered for this area, <br />and will be required for the overall system to ensure timely maintenance and performance to the intended <br />design. What are the proposed finished elevations on those private garages back there? A stormwater <br />analysis using EPASWMM or equivalent software that provides dynamic routing and evaluates surcharge <br />impacts must be prepared. <br />Please provide additional information on the proposed courtyard internal to this facility; drainage patterns_ <br />are unknown and inust be accounted for in some fashion. Also, clarify where the site design for this <br />project ends and that of the future parking ramp expansion begins as the surface parking area shown as <br />"ramp addition" is unclear on how drainage will be accomrnodated. Integration with the parking ramp <br />expansion is key to the successful design of both facilities and coordination must be understood on <br />utilities/drainage, dedicated parking, access locations, grades/elevations and transitions.There appears to <br />be a coordinated storm sewer effort between this project and the Suite Living project to the west; private <br />cross drainage easements will be required to outline responsibilities of each entity as • it relates to <br />ownership, maintenance, etc. Are the proposed stubs to the west property adequately sized to handle to <br />proposed runoff from that site (building, paved areas, etc.)? , - <br />Please explain how the proposed site storm sewer connections will be made to the existing public system <br />in the right-of-way. Are the receiving structures adequate in size and downstream capacity to accept the <br />runoff from this project? All impacts to existing infrastructure for curb cuts and utility connections <br />(streetlights, hydrants, catch basins, streetscape, roadways, etc.) must also include a relocation/restoration <br />plan, not just notes calling out the. removals. Notes and details must be added showing impacts to the <br />structures and roadways, methods of connections, and mitigation/restoration; including sawcutting, <br />coring, closures, timing, etc. <br />Is there any dewatering required for this project? If so, the appropriate permit must be secured from the <br />DNR, and the City will want to review the dewatering plan prior to hnplementation. No dewatering <br />activities can occur until the required permit is secured and submitted for review. <br />Additional permits that will be required include, but are not limited to, an NPDES construction permit <br />from the MPCA (which includes a SWPPP plan), LRRWMO, right-of-way, and City contractor's license. <br />74 <br />