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I <br /> iion— a = n <br /> 5TORMWATER <br /> 1,,r . sow-nONs INC <br /> IJuly 20, 2011 <br /> I Steve Pesce <br /> PACLAND <br /> 11711 SE 8th Street, Suite 303 <br /> 1 Bellevue, Washington 98005 <br /> RE: StormFilter Review, Seaway Lot 3B and Norpro Building B Project <br /> CONTECH Stormwater Solutions Inc. has reviewed the plans showing the StormFilter stormwater treatment <br /> I system for the Seaway Lot 3B and Norpro Building B project in Everett, Washington. The original plans were <br /> prepared by WH Pacific, but additional flow from the Norpro Building B site will be added.The new design is <br /> being prepared by PACLAND. <br /> IThe original mass-loading design was for a total basin size of 0.38 acres,with 0.25 acres of pollution generating <br /> impervious surface and a 2 year release rate from the upstream detention system of 0.002 cfs. The new Norpro <br /> building design will add an additional 0.23 acres of roof runoff and 0.08 acres of landscape, which is considered <br /> I NPGIS and will increase the total release rate to 0.0036 cfs. The total peak flow rate resulting from the 100-year <br /> release rate will be less than 0.23 cfs. The original design utilizes a 48" Manhole StormFilter unit with 2 filter <br /> cartridges and ZPG filter media and will be sufficient to handle the increase in flow from the Norpro site(see <br /> I attached mass-loading calculations). <br /> Two 7.5-gpm filter cartridges will treat 0.033 cfs,which meets the treatment requirement. Since the internal <br /> I <br /> bypass capacity of the 48" Manhole StormFilter is 1.0 cfs,the StormFilter may be used online as shown on the <br /> plans; a separate high flow bypass structure is not required. <br /> In summary,the StormFilter is expected to operate in accordance with CONTECH Stormwater Solutions' design <br /> I intent. Please note that CONTECH Stomiwater Solutions has not reviewed the hydraulics of the collection <br /> system upstream or downstream of the filter. <br /> IPlease do not hesitate to call if you have any questions or require more information. <br /> ISincerely, <br /> At, Jr' m.. <br /> Kathryn Thomason, P.E. <br /> I Stormwater Design Engineer <br /> CONTECH Construction Products, Inc. <br /> I <br /> 1 <br /> ©2006 CONTECH Construction Products Inc. 11835 NE Glenn Widing Dr.,Portland OR 97220 Page 1 of 1 <br /> www.contech-cpi.com Toll-free:800.548.4667 Fax:800.561.1271 TS-P052 <br />