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Stormwater Technical Memo Project: 20090010 Swift Bus Rapid Transit Northern Terminal at Everett Station Perteet TO: George Baxter, Everett Transit CC: File FROM: Erik Emerson, PE DATE: May 13, 2009 RE: Documentation of Stormwater Standards Compliance The Swift Bus Rapid Transit (BRT) North End Station will be constructed in a portion of the Everett Station complex south of the existing bus platform and west of the newly constructed Sound Transit train platform. The purpose of this memorandum is to document the project's approach to storm water quality treatment and flow control requirements. No storm water mitigation facilities are proposed for the project due to the following: 1. The project lies within the North Everett combined sewer zone. Water quality treatment is therefore not required due to the treatment received in the City's sewer treatment plant. Detention is only required in this zone for pipe capacity issues. 2. The site currently drains to a detention facility installed during the construction of Everett Station to mitigate capacity issues due to that project. Since the BRT project lies within the limit of the original collection area for this detention system the proposed development's flow impacts have already been accounted for by the original project. 3. The site is currently nearly 100% impervious.The project will not increase, and will likely show a minor reduction in, the total impervious area on the site. Under City of Everett drainage code the project would not be required to provide improvements for treatment or detention because there is no increase in impervious area and correspondingly no increase in site runoff. 4. Sound Transit is completing the construction of a parking lot and pedestrian overpass project within the bounds of the Everett Transit complex. As part of this plan the BRT site was anticipated to be turned into a parking lot. Permits were issued for these improvements prior to the BRT project beginning. Since no additional storm water improvements were required for the Sound Transit design it is assumed that the BRT project will not require them either. During preliminary design of the project the City of Everett indicated that this assessment appeared to be correct. At the time the City's main concern was the Swift BRT North Terminal at Everett Station Page 1 Documentation of Stormwater Standards Compliance Stormwater Technical Memo