Agenda - Public Works Committee - 04/21/2009

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CASE # ~ DISCUSSION OF STORM SEWER IMPROVEMENTS WITHIN ALPACA ESTATES FOR RAMSEY.COMMONS By: Tim Rimmer, City Engineer Background: The Ramsey Commons project was approved by CityCounci~ on May 13,2008. The project is located at the northwest comer of Armstrong Boulevard and Riverdale Drive. It consists of a 7,800 square foot mu1ti~tenant building, which includes a drive through for a US Bank. The parcel description is Lot 1, Block 1 ALPACA ESTATES and is subject to the City'sstormwater managemenfrequirements fgr developments. The property owner/developer also owns the p~operty directly to the west, which is described as Lot 7, Block 1 ALPACA ESTATES 4TH ADDIrON. There is an existing regional storm basin at the west end of Riverdale Drive that was created for the benefit of ALPACA ESTATES 4TH ADDITON. As part of the site plan application the property ovvner decided to split the regional ponding capacity equally between the two parcels that they own, therefore requiring some on-site. stormwater ratl:) and quality control for each lot. The idea was to develop Lot 1, Block 1. with a reduced on~site ponding requirement, and then duplicate . the process for Lot 7, Block 1 when a proposal came forward in the future. The applicant would construct the reduced on-site ponding required as part of the initial development, including a discharge pipe down to the regional basin approximately 1000' to the west. There is existing storm sewer in Riverdale Drive approximately 600' to the west but it is undersized to accommodate any additional flow, therefore a separate pipe would be required to carry the discharge from their proposed on-site pond to the regional basin. The applicant's initial design was to discharge water directly from their on-site pond into the Riverdale Drive right-of~way and allow it to flow down the street to the existing storm sewer causing additional ponding concerns on the roadway. Observations: ,. The case brought before Council at the time of approval outlined a process that the City was willing to undertake to construct the storm sewer to accommodate the applicant's properties, as well as future development along Riverdale Drive within ALPACA EST A TES 4TH ADDITION. The applicant was going to construct a temporary basin on Lot 7, Block 14TH ADDITION to retain all the runoff from both their sites until such time that the City installs a trunk storm sewer line along Riverdale Drive to the regional basin. It was suggested that this might be accomplished in conjunction with the Armstrong Boulevard improvements planned for 2009. The applicant would pay their stonnwater management fees for both lots and deposit the estimated cost of the improvement in escrow as a funding mechanism to justify the project. The City's obligation would be to pay for the cost of oversizing the pipe, and the installation of other features necessary to serve the larger drainage area. These additional City costs would be recouped through future stonnwater management fees from the undeveloped benefiting parcels, and quarterly storm water utility charges. The developer is now considering advancing the stonn sewer trunk installation as part of their development project. It is estimated that the total project cost for this trunk line is approximately $60,000, and the City oversizing cost is approximately $15,000. The property owner is requesting a process to recoup some of their capital investment for this trunk line installation, with a potential payback over time as others in the area develop and connect. 7