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24,4's <br /> CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br /> Include computer printouts,calculations, equations,references,storage/volume tables,graphs as necessary <br /> to show results and methodology used to determine the storage facility volumes. Where the Western <br /> Washington Hydrology Model(WWHM)or other approved continuous runoff model is used,its <br /> documentation files shall be included. <br /> E. Develop a Stormwater Treatment Plan <br /> The step-by-step process in Chapter 4 of this volume must be used to determine the type of treatment <br /> facilities applicable tothe project. <br /> Oil control facilities for runoff treatment must be located upstream of treatment and detention facilities and <br /> as close to the source of oil-generating activity as possible. Table 3.1 summarizes placement considerations <br /> of other treatment facilities in relation to detention. <br /> Table 3.1 Treatment Facility Placement in Relation to Detention. <br /> . � may►' � <br /> Water Quality Facility Preceding Detention (Following Detention <br /> Filter strip OK No—must be installed before flows <br /> (Volume III, Chapter 6) concentrate. <br /> Basic or large wet pond OK OK—less water level fluctuation in ponds <br /> (Volume III, Chapter 7) downstream of detention may improve <br /> aesthetic qualities and performance. <br /> Basic or large combined Not applicable Not applicable <br /> detention and wet pond <br /> (Volume III,Chapter 7) <br /> Wet vault. OK OK <br /> (Volume Ill, Chapter 7) <br /> Basic or large sand filter or sand OK with OK—sand filters downstream of detention <br /> filter vault pretreatment facilities may require field adjustments if <br /> (Volume Ill, Chapter 5) prolonged flows cause sand saturation and <br /> interfere with phosphorus removal. <br /> CMedia Filters OK Not OK for some types of media, such as <br /> compost Z?'UV OI *4i1 <br /> Stormwater treatment wetland/ OK OK—less water level fluctuation land better <br /> pond (Volume Ill, Chapter 7) plant diversity are possible if the stormwater <br /> wetland is located downstream of the <br /> detention facility. <br /> In the Stormwater Treatment Plan, include a drawing of the proposed treatment facilities,and any structural <br /> source control BMPs. The drawing must show overall measurements and dimensions,placement on the <br /> site, location of inflow,bypass,and discharge systems. <br /> Drainage from non-pollution generating impervious and pervious surfaces does not require treatment. <br /> However,if runoff from non-pollution generating surfaces reaches a runoff treatment BMP,flows from <br /> those areas must be included in the sizing calculations for the facility. Once runoff from non-pollution <br /> generating areas is mixed with runoff from pollution-generating areas,it cannot be separated before <br /> treatment. <br /> Runoff from backyards can drain into native vegetation in areas designated as open space or buffers. In <br /> these cases,the area in native vegetation may be used to provide the requisite water quality treatment, <br /> provided it meets the requirements outlined in Volume III,Chapter 12 for dispersion. <br /> Volume I—Minimum Technical.Requirements <br /> 3-7 <br />