Agenda - Council - 11/23/2010 - Laserfiche WebLink

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Preliminary Site Plan Review- Residence at The COR October 28, 2010, revised November 17, 2010 Page 6 of 9 The following comments are offered regarding the October 15, 2010 plans by Emanuelson -Podas Consulting Engineers: Grading and Drainage: The building floor elevation should be set to be above the adjacent grade of the public streets while meeting ADA accessibility guidelines. The grade from the building to the property lines and extending to the limits of the shared accesses must be set to match the plans for the future buildings and parking. The COR Development utilizes regional stormwater ponds for rate control and water quality treatment. Each individual site needs to provide additional water quality treatment through the use of rain gardens, water quality treatment structures, or other BMP's. The plan is proposing to install a conventional system sewer system (inlet structures and pipes) that lead to discharge points into the existing storm sewer system adjacent to the site. Drainage calculations were received but additional information is required for the appropriate sizing of the proposed Aqua -swirl structures. The AS -3 and AS -4 devices may handle the water quality treatment flows; however, the outlet pipe sizes are 10 "/ 12" respectively and do not match the design pipe sizes of 15" and 18" shown on the storm sewer plans; the AS -7 and AS -8 devices have adequate outlet sizes and will provide treatment for up to the 10 year event. Additional BMP's should also be considered and investigated to provide for some rate control and lessen the need for downstream piping /structure sizing, and reduce the volume of water leaving the site. Please identify overflow routes for all the "ponding areas" around catch basins, especially in area 4 between the parking ramp and proposed liner building. Explain drainage patterns and overflow routes should one or more of these basins become clogged and /or frozen; it appears as if only 2.5" of freeboard is proposed from the entrances on the back side of the proposed liner building. The City currently experiences freezing problems with the floor drains in the parking ramp and we do not want to take additional drainage into our stormwater system. A maintenance plan should be considered for this area, and will be required for the overall system to ensure timely maintenance and performance to the intended design. What are the proposed finished elevations on those private garages back there? A stormwater analysis using EPASWMM or equivalent software that provides dynamic routing and evaluates surcharge impacts must be prepared. Please provide additional information on the proposed courtyard internal to this facility; drainage patterns are unknown and must be accounted for in some fashion. Also, clarify where the site design for this project ends and that of the future parking ramp expansion begins as the surface parking area shown as "ramp addition" is unclear on how drainage will be accommodated. Integration with the parking ramp expansion is key to the successful design of both facilities and coordination must be understood on utilities /drainage, dedicated parking, access locations, grades /elevations and transitions.There appears to be a coordinated storm sewer effort between this project and the Suite Living project to the west; private cross drainage easements will be required to outline responsibilities of each entity as it relates to ownership, maintenance, etc. Are the proposed stubs to the west property adequately sized to handle to proposed runoff from that site (building, paved areas, etc.)? Please explain how the proposed site storm sewer connections will be made to the existing public system in the right -of -way. Are the receiving structures adequate in size and downstream capacity to accept the runoff from this project? All impacts to existing infrastructure for curb cuts and utility connections (streetlights, hydrants, catch basins, streetscape, roadways, etc.) must also include a relocation/restoration plan, not just notes calling out the removals. Notes and details must be added showing impacts to the