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l <br /> ( <br /> i <br /> � Thc options for storm �vatcr u�catmcnt for mulitiplo-family, commercial, and industrial projects <br /> in thc City of Gvcrctt arc: <br /> ( <br /> 1 a) an infiltr..tion Uasin, iP suitablc soils cxist on the sitc <br /> � b) a wetpond <br /> c) ,�construcled wctland <br /> ' d) a SMI 5tonnFilter, with prctrcatmcnt <br /> All storm watcr facilitics shall Uc dcsigncd in :iccordancc with cuiTcnt and applicablc City <br /> � st�ndards and/or design policics. <br /> � <br /> � The follo�vins arc Ihe Cih�'� current dcsi��n �olicies f�r use of SMI StormFilters for stonnwater <br /> � trcaUnent: <br /> I) Thc SlormPiltcr must bc preceded by a pre[rcat�ucnt wetvaulUtank containing at Ieast <br /> 30% of lhe 6-month, 24-hour stonn runoff volumc from the contributing, dcveloped <br /> drainr,gc arca; or by anodicr prcucatment systcm that has rcceivcd a General Use Level <br /> Dcsignation (GULD) from thc Washington State Depa�lment ef Ecology. <br /> 2) The 5torm�ilter must lreat, at a mininmm, thc developed pcak 11o�v from the contributin� <br /> � area for thc 6-month, 24-hour storm. <br /> i 3) The StormPilter caru•idges shall bc designed �vith a maximunt ilow rate of 15 epm per <br /> � cartridge, if SBUI-1 or a comparaUle single-event hydrological model is used ro gener:te <br /> the Ilows. IP the �\�'1'HM is used to gencrate the ilo���s, lhc dcsign ilow per carlridgc <br /> � shall be 7.5 gp�». i��s�, no,,.s si,,,u ��i,ypassed around the StormFilter vault, Uut should <br /> ( gencrally pass through thc pretreatmcnt devicc. <br /> � 4) The StormPilter media shall larget dissoh�ed pollutanls and nutrienls, in addition to total <br /> � suspended solids. As more effective media become available in the future, thc <br /> StormPilter shall be upgradcd, dw•ing routinc cartridge replacement, to uti!ize these <br /> � impro��ed mcdia. <br /> � 5) The SlormPilter shall Ue designed with the mininuun hcad differential behveen inlet :mJ <br /> outle[ tha� is recommendecl by the manufacturcr for the speciGc model used. <br /> � Downstrcam hydraulic calculations will bc performed to demonstrate that downstrrun <br /> condilions will c�mse backwater conditions Ihat reduce thc hydraulic potential across thc <br /> � filter to Icss than what is reconuucnded by Ihe manuFacWrcr. <br /> � 6) R :tinc mainlcnance of the Stornil�ilter is required. A dctailed operation and <br /> maintenance plan for thc system must be prepared tor approval by the City. A certiticatc <br /> � of system maintenance must Ue submitted ro lhe City annualiy. <br /> ( 7) Dlaintenance anrl operation of the StormPiltcr on tliis sile sha�l be adapted, in U�e future, <br /> � to rct7ccl tl�c ctu•rcnt knowlcdge rc�arding this cmcrging tcchnolor�y. <br /> 3) All olher applicable, and non-conllicting, crite�:a in the current edition of SIvll's Product <br /> llesign A�;.uival shall be I'ollo�.ved in thc design, constniction, and maintenancc of thc SMI <br /> Stormriitcr on this sitc. <br /> 9) Por StormPiltcrs located do�vnstream of dctcntion systems, the Sn41 mass loading design <br /> � procedure, wi�h the 1'ollo�ving .ssumptions, shall be utilized: <br /> a. 'I'SS rcmoval rcquircd = SO�b <br /> b. Assunted SO�o TSS rcmn��;d efficiency ibr prcu•catment dcvice �vith DOG GUi_D. <br /> � S:\jzimmcrm\���i�rJ\StonuPiltcrdcsen.doc <br /> ( Primc�IS/'I/_'UOI, <br /> � <br />