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

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Final Site Plan Review -Suite Living at The COR December 8, 2010 Page 6 of 10 Engineering Review Reviewer: Tim Himmer, City Engineer thimmer (dci. ramsev. mn. us 763 - 433 -9893 The following comments are offered regarding the December 3, 2010 plans by Landform Engineering Company: 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 improvements. There appears to be discrepancies between the overflow locations along the west side of the building and the landscape plan; care should be taken to ensure that installed plant material does not restrict flow through this area or flooding concerns could be realized. 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 storm sewer system (inlet structures and pipes) with the east half of the site discharging to a proposed design on the adjacent Residence at the COR property and ultimately to the public system, and the west half directed into the public system in Sunwood Drive. Drainage calculations were received but additional information is required for the appropriate sizing of the proposed treatment structure /manhole at the discharge points (Ecostorm structure). The model was developed showing this structure 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 CB overflow and ponding in the low areas of the parking lot and green space. 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. 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 the proposed coordinated storm sewer effort between this project and the Residence at the COR to the east; private cross drainage easements will be required to outline responsibilities of each entity as it relates to ownership, maintenance, etc. All proposed contours must be tied into existing contours of the surrounding area, and extend 100' beyond the property limits. Since the development of lots 3, and 4 are interrelated with regards to constructability and drainage, future revisions to the plans should include an overlap of the grading plans. A maintenance agreement will be required for the overall system to ensure timely maintenance and performance to the intended design. The proposed site storm sewer connection 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