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The existing portables were constructed in 2015. Roof runoff from the portables drains to gravel <br />pads under the portables that serve as infiltration facilities. The Stormwater Technical <br />Memorandum for the 2015 portables project is included as an attachment in Appendix C of this <br />report. Stormwater design for the two proposed portables will use a similar approach. <br />METHODOLOGY <br />Drainage design for the project is based on City of Everett Municipal Code (EMC) 14.28, <br />Surface and Storm Drainage. <br />The EMC 14.28 refers to the Washington State Department of Ecology's (DOE) Stormwater <br />Management Manual for Western Washington (Stormwater Manual) for the city's stormwater <br />technical manual. <br />Western Washington Hydrology Model (WWHM 2012) is used for runoff and stormwater <br />management modelling. <br />This project is categorized as a redevelopment project adding more than 2,000 square feet of <br />hard surface area but less than 5,000 square feet of hard surface area and is subject to Minimum <br />Requirements #1 through #5 in the Stormwater Manual. <br />Stormwater management design for this project uses infiltration in gravel infiltration beds under <br />the portable buildings. The Low Impact Development (LID) performance standard is met by <br />infiltration. WWHM calculations demonstrating compliance are included in Appendix B. <br />Stormwater Site Plan, Including SWPPP 2 - u <br />Silver Lake Elementary School Portables <br />