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Verizon Communications- Stormwater Site Plan Everett, WA <br /> Water Quality <br /> Y <br /> ' Despite the fact the site is currently developed, water quality is required to be provided for <br /> the new or replaced pollution generating surfaces. However, the proposed water quality <br /> ' facility has been sized to accommodate all the pollution generating and non-pollution <br /> generating surfaces. The areas used to calculate the size of the water quality facility are as <br /> shown in Table 5 below: <br /> Table 5 <br /> Water Quality <br /> Only areas affected by development included in calculations. <br /> ' SF Proposed <br /> AC <br /> Pervious 78,745 1.80 <br /> Impervious (PGIS & NPGIS) 318,504 7.32 <br /> TOTAL 397,249 9.12 <br /> To satisfy the project's water quality requirements, a pre-settling chamber and a Contech <br /> StormFilter Vault will be installed. A flow splitter will also be installed to allow higher <br /> flow events to bypass these structures. <br /> ' Basin Data PCN Calc PTC Calc DCI-CN Calc DCI-TC Calc Compute Runoff for Design Event <br /> Select Design Evert: WQ Compute <br /> AMC for this Computation: <br /> AMC1 • AMC2 AMC3 Project AMC:2 <br /> ' Static <br /> Peak <br /> ' Time to PRate:eak: 480.001.8132 mcfs in.(8.00 hrs) <br /> Hydrograph Vol: 28629.25 cf(0.6572 acft) <br /> ===>Computation is+/-99.9967%of theoretical for time step of 10.00 min <br /> Close Apply I <br /> SBUH methodology and StormShed software were used to calculate the site discharge and <br /> to size the proposed water quality facilities. Per the DOE Manual, the water quality flow <br /> ' rate is calculated from a rainfall that is 72% of the 2-year, 24-hour event. The rainfall for <br /> the 2-year, 24-hour event, per the City of Everett Stormwater Manual, is 1 .55 inches. <br /> Therefore, the 6-month, 24-hour (water quality) event rainfall is 1 .12 inches. The peak <br /> flow for the water quality event for the fully developed, 9.12 acre site is approximately <br /> 1 .81 CFS and 28,629 CF of storage volume. <br /> PACLAND Job# 50183001 Page 21 <br />