31 SW EVERETT MALL WAY 2018-01-02 MF Import

Labco Auto Body Repair Facilely Drainage Report, May 20, 1991 Page 2 The proposed drainage facilities for this taevelopment include curbing to transport water to catch basin, a storm water collection and detention system. Outlet structures with orifices will meter the collected storm water to match the pre-devebnment flow rates off the site. The Everett Drainage Ordinance No 670-60 is 4isoof ,,au.., e�uating the sites runoff characteristics and %%4ien sizing the sites stor *4der detentior id ` As directed by the AS, City of Everett a 5-year, 24 hour storm fregW.?cy'� used to estiill~allowable release rate for the site and for sizing the bio-filtration A. 25-year, 24 a„ the frequency is used for sizing the stone water detention sys"). The Everett Draina;e Cal -,nation Submission Form was used to estimmF storm waver runoff, required storm ester as+denbon and orifice sizing for the storm water ot+ntrol s+ n�lure. It is proposed lh@l & daserMon system's flow control structure be construrcted wi11h two orifi6es. This approach,omovek ne peaks off the smaller frequency stone€ �e,id Provides additional protet;;fion to the downstream conveyance sYitem. Stone water runoff from the building roof and paved areas will be conveyed through a series of catch basins and 12 inch diameter conveyance piping to a 36-inch diameter underground detention tank located north of the proposed building. Storm water discharged from the detention facilities at a rate equivalent the 5-year pre -developed flow rate will be directed to an oil -water separator. Discharge from the oil -water separator will be conveyed to the bio-filtration swab. swale for final polishing. For storms with a discharge greater than the 25-year event, the flow will be directed by the control structure to the existing ditch line along the east edge of the site. The portions of the site disturbed by construction and not covered by surface parking or building foot print will be landscaped or hydroseeded to protect against erosion. A temporary erosion plan is provided for the control of storm water construction activity. TIRIAaco.WPS