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1 <br /> 1 <br /> ' Stormwater Detention Criteria <br /> Design detention using StormSHEDTM single event program(1992 Department of Ecology <br /> (DOE) SBUH flow control standard) and ensure the detention passes the program's testing <br /> ' routine. Factor of safety included in the design according to the Everett Stormwater Manual. <br /> Precipitation Values <br /> ' Precipitation values for the 24-hour storm are shown below based on the COE Stormwater <br /> Management Manual. <br /> ' 6-month 1.12 inches <br /> 2-year 1.55 inches <br /> 10-year 2.25 inches <br /> 25-year 2.60 inches <br /> 100-year 3.25 inches <br /> Water Quality Treatment <br /> ' • Filterra Bioretention Systems. The Western Washington Hydrologic Model(WWHM) <br /> software program is used to size the Filterra units. <br /> ' • Bypass flows greater than the required treatment rate. <br /> • Provide basic treatment. <br /> • Percent filtered is greater than or equal to 91 percent,modeled as sand filter in WWHM <br /> ' program. <br /> Other Criteria <br /> SEPA: Not available at this time. <br /> ' PROPOSED DRAINAGE CONDITIONS <br /> The James Monroe Elementary redevelopment project includes the construction of a building <br /> ' with a 46,000-square-foot footprint, a covered play area,accessory buildings, adjacent parking, <br /> and a fire access road. The existing structures and storm system on the property will be <br /> demolished,but the existing athletic field and the northwest portion of the site will remain <br /> ' undisturbed. The existing drainage pattern of runoff collection and conveyance through storm <br /> drain pipe and catch basins will not be altered. The existing discharge location for site runoff <br /> will remain intact and the proposed drainage system will connect to it. <br /> ' Runoff from pollution-generating impervious surfacing is designed to drain as sheet flow across <br /> the surfacing and along the concrete curbs. Runoff will be directed to the proposed Filterra <br /> Bioretention structures located throughout the paved parking area. The Filterra systems release <br /> to a proposed underground detention system located along the western boundary of the site. The <br /> detention system will be composed of StormTech Chambers surrounded by crushed rock that <br /> James Monroe Elementary School 4 Reid iddleton <br /> Drainage Report <br /> 1 <br />