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1 <br /> E. Stormwater Treatment Plan <br /> Narbeck Creek: <br /> ' Since all runoff draining to Narbeck Creek is from non-pollution generating surfaces, no additional <br /> stormwater treatment BMPs are proposed. <br /> ' Powdermill Gulch Creek: <br /> Stormwater treatment for the Powdermill Gulch Creek basin will be provided through source <br /> control and by a compost stormwater filter. Source control will be achieved by keeping roof <br /> leaders separate from surface runoff until downstream of the water quality facility to the maximum <br /> extent practicable. A Contech StormFilter will be provided to treat all onsite runoff from pollution <br /> generating surfaces within the Powdermill Gulch Creek basin. A Vortech 1000 structure is <br /> ' provided upstream of the StormFilter for presettling. <br /> The small parking area in the southern portion of the existing development will receive runoff <br /> treatment via a StormFilter Catchbasin. The structure has a built in baffle wall chamber to separate <br /> Idebris from the runoff prior to being routed through the compost filter. <br /> The following WWHM3 calculations were utilized to size the StormFilter facility: <br /> Western Washington Hydrology Model <br /> PROJECT REPORT <br /> ' Main Site <br /> Project Name: PMGC <br /> 11 Site Address: 23rd Dr W <br /> City Everett, WA <br /> Report Date : 7/20/2011 <br /> Gage Everett <br /> ' Data Start : 1948/10/01 <br /> Data End 1997/09/30 <br /> Precip Scale: 0.80 <br /> WWHM3 Pro Version:homith afiom3 1 a <br /> sna infd <br /> raj I.-it <br /> o� �31 3 3 3 <br /> a 9/6�� isJ k 3 M: 7 <br /> -�" ��' j!kielm $ •'[tie}� � <br /> '[f3 ;c it <br /> OMB ffff <br /> ran e 4 Y 3 <br /> r Y 1 <br /> 6/16/2011 Stormwater Site Plan Page 29 <br /> 1 <br />