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Kennedy Jenks <br /> Technical Memorandum <br /> Kyle Bringedahl, The Boeing Company <br /> 13 April 2021 <br /> KJ 2096009.00 <br /> Page 5 <br /> Modeling results are included in Attachment A. <br /> 1.5 Results <br /> Table 3 shows the results of hydrologic and hydraulic modeling for the existing and proposed <br /> systems. The proposed system improves treatment capture efficiency from 62.5 to 95%, <br /> significantly decreasing the volume of water that discharges without treatment, maintains the <br /> same number of spillway events over a 30-year period for storm events exceeding the 25-year <br /> 24-hour event, and increases the system's probability of meeting the copper and zinc NELs. <br /> The model results show that the proposed stormwater system meets or exceeds flow control <br /> and treatment criteria for the existing system. <br /> Table 3. Comparison of existing and proposed system performance <br /> Existing <br /> Conditions Proposed <br /> as (Hybrid <br /> Performance Metric Designed Alternative) <br /> Capture Efficiency (%) 62.5% 95% <br /> Average Annual Bypass Days 81 11 <br /> Days with Bypass (%) 22.1% 3% <br /> Average Annual Bypass Hours 682 73 <br /> Probability of Meeting Copper NEL (%) > 80% > 99% <br /> Probability of Meeting Zinc NEL (%) >40% > 99% <br /> Enclosure(s)Attachment A- Hydrologic/Hydraulic Modeling Output Data <br /> cc: Kevin Hanefeld <br /> 1\kjc.locallkjc-rootlkj-projectslfederalwayl202012096009.00 boeing everett sw treatment109-reports19.08-reports-tmslcity of everelt design tmlboeing everett sw design tech memo.docx ©Kennedy/Jenks Consultants, <br /> Inc. <br />