2102 ROSS AVE 2025-07-28 - Laserfiche WebLink

landscaping, buffer enhancement, estuarine wetland creation and untouched riverside. The ' impervious areas are divided into pollution generating surfaces and non-pollution generating surfaces. Pollution generating surfacing will be routed to one of several DOE approved Contech Stormwater StormFilters sized to treat a small tributary basin. The project will discharge at the ' ordinary high water elevation of the existing drainage ditch on Ross Avenue in order to mimic predevelopment hydrology and drainage patterns. The coated metal rooftop area is a non- pollution generating surface and will be discharged directly into the bioswale/ditch system along Ross Avenue. See Appendix for WQ Analysis and Design A 24-hour storm with a 6-month return frequency was used for the flow control treatment design of the proposed Contech StormFilters. Continuous modeling using Western Washington Hydrologic Modeling (WWHM 3) was used for obtaining the design flow volume (QwQ). Calculations are shown in Appendix C and the developed drainage flow ' is tabulated below: Basin A: QwQ=0.088 cfs Basin B: QwQ=0.205 cfs ' See Appendix C for additional information and visual representation of the drainage basin map. D. Stormwater Flow Control Plan ' According to the 2010 City of Everett Stormwater Management Manual and Appendix I- E from the DOE manual, Flow Control is not required,because the site discharges into an exempt receiving Water Body. ' E. Stormwater Treatment Plan Pollution generating surfacing will be routed to a DOE approved Contech Stormwater StormFilter® with Metal Rx media sized to treat the tributary basin for enhanced treatment. There are two separate drainage basins for the proposed improvements. Basin ' A includes runoff from the lot in the northwest corner of the project site and Basin B includes runoff in the southeast corner of the project site between the proposed wharf and Ross Avenue. ' Runoff from Basin B is currently treated by a 7-cartridge stormfilter manhole with pre- treatment settling vaults. The addition of impervious surface created by the proposed crane pad in Basin B was modeled using WWHM3 and results indicated that the 7- ' cartridge stormfilter manhole has sufficient capacity to treat the additional runoff produced. See Appendix C for Western Washington Hydrologic Modeling (WWHM3) and sizing of the Contech StormFilter. i Stormwater Site Plan Page 17 ' McClean Ironworks Site Improvements August 2014 I