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I <br /> Verizon Communications-Stormwater Site Plan Everett, WA <br /> The StormFilter Vault was sized usingthe SBUH flow converted to an equivalent WWHM <br /> q t <br /> flow, as presented below, along with the sizing recommendations from Contech. <br /> IWWHM Sizing <br /> Per the 2005 DOE Manual, Figure 9.6b provides the required ratio to apply to the water <br /> I quality treatment flow rate. That chart specifies that for a 6-month, 24-hour precipitation <br /> of 1.12 inches, the ratio (k) to apply is 2.80. The chart is shown below and the calculation <br /> showing this factor applied to the water quality flow rate is also shown below. <br /> 1.8132 CFS/ 2.80 = 0.65 CFS <br /> 1 0.65 CFS x 7.48 Gallon x 60 Seconds = 292 GPM <br /> Seconds 1 CF 1 Minute <br /> IWith WWHM sizing, the 27"-tall Contech StormFilter cartridges have a treatment flow rate <br /> of 11.25 GPM. Therefore, based on WWHM sizing, the number of cartridges required is: <br /> 111 292 GPM/ 11.25 GPM/cartridge = 26 cartridges <br /> This calculation is confirmed with the Contech Stormwater Treatment System Calculations, <br /> I <br /> shown below. Therefore, this project proposes to provide 26-27" cartridges installed <br /> within an 8'x16' StormFilter Vault. <br /> I <br /> SBUH Peak/WWHM Off-Line 15-min WO Flow Ratio vs <br /> I6-Month Precipitation for 0%to 100%Impervious Areas <br /> R 7.0 <br /> a 6.0 <br /> t <br /> i 5.0 <br /> o <br /> (K) 4.0 <br /> y 3 - <br /> spo, <br /> • <br /> 2.0 1 <br /> 1.0 t <br /> 0.0 0.5 tot"— 1.5 2.0 2.5 3.0 3.5 4.0 <br /> 6-month,24-hr precipitation(72%of 2-year),Inches <br /> IFigure 9.6b—Ratio of SBUH PeakIWQ Flow <br /> I <br /> IPACLAND Job# 50183001 Page 22 <br />