Agenda - Council - 12/14/2010 - Laserfiche WebLink

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Final Site Plan Review Residence at The COR December 8, 2010 Page 7 of 11 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 ramp expansion. The COR Development utilizes regional stonnwater 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 treatment structures /manholes at the discharge points (Aqua - swirl and Ecostorm structures). The model was developed showing these structures as a reach, and therefore no outlet pipe sizing was provided at the tie -in to the public system; this info must be incorporated into the model to justify treatment structure sizing and removal efficiencies, and resubmitted for review prior to issuance of a building permit. The model must also be revised to account for the entire contributing area (including the courtyard), as the flooding elevations for the ponding areas around catch basins exceeds the first floor elevation of the building (broad crested weir input for overflow points). 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 the courtyard area and alleyway between the parking ramp and proposed liner building. While the revised plans provide spot elevations and call out overflow points to explain drainage patterns, the model does not provide the same level of detail and must be revised accordingly, including the 100 year event with a partially blocked pipeThe City currently experiences freezing problems with the floor drains in the northeast corner of the parking ramp and we do not want to take additional drainage into our stormwater system; rather we would like to connect that existing system into the proposed storm sewer line in the alleyway for an additional overflow point from the existing system. The proposed grades of the alleyway are not tied into the grades of the existing parking ramp, and it appears as if up to 2' of grade different will be experienced; how do you intend to treat this grade differential relative to appearance, safety, and drainage? 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. Please provide additional information on the proposed courtyard area;is the proposed storm sewer in this location intended as a separate line from the roof drainage ?. A combined line is not recommended. Integration with the parking ramp (existing and proposed 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. All proposed site storm sewer connections into the existing public system in the right -of -way must be constructed with RCP pipe; no PVC or HDPE is allowed. The model must also be submitted to City staff to verify that the receiving structures are 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 be coordinated with City personnel prior to impacts. These impacts should also include irrigation, bedding material, structural soils, etc., not just