Agenda Packets - 2008/12/22 - Laserfiche WebLink

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December 22, 2008 Item No. 7C Page 3 x Infiltration Basins: The original 2007-2008 Feasibility Report prepared in December 2006 had laid out the preliminary approach to stormwater infiltration, based on an anticipated change in the Rice Creek Watershed District (RCWD) rules. RCWD did in fact adopt their new rules on February 13, 2008. In response to the new RCWD rules, and recognizing their large impact on the overall Street and Utility Improvement Program, the City developed the SIP during the summer of 2008. The components of the SIP were based on compliance with the approved RCWD rules, and were adopted via Resolution 7319 on August 11, 2008. Although RCWD had adopted their new rules in February, they continued work throughout the summer and fall of 2008 on developing standardized tools, including calculation worksheets, to apply the new rules to project permit submittals. RCWD also experienced change in Staff and consultants during this time, slowing progress on the development of these tools. It was critical that the City receive clear direction for applying the rules to the 2009-2010 Street and Utility Improvement Project, so the process could be used with consistency throughout the remaining projects in the overall Program. Therefore, we maintained frequent communication with RCWD Staff and Consultants regarding the calculation methods and permit application tools. The final direction from RCWD in regard to the required calculations and permit application tools was received by the City on October 30, 2008. However, in order to keep the 2009-2010 Street and Utility Improvement Project on schedule and allow time for the SIP appeal process, the proposed locations of infiltration features needed to be identified by the end of September. The locations were determined based on initial feedback from RCWD on preliminary calculations performed by the City. Based on those preliminary calculations, a total of 117 features were identified, affecting 104 properties. Notifications were sent to those affected properties on September 26, 2008. The final direction from RCWD in late October on the application of the rules included a much broader approach to the infiltration calculations. Based on these final calculations, it was possible to reduce the number of infiltration features on the project. Those basins that were in the best locations, provided the most benefit, and had the best construction characteristics were kept in the project. Those eliminated were the ones located in less desirable locations from a drainage standpoint, those providing smaller volumes, and those which would have been more difficult to construct.