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Capacity and I/I Assessment City of Redwood City (0011239.02)3-12 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 It should be noted that SVCW is in the process of upgrading the headworks to its treatment plant, which includes re- alignment of the force main that enters the plant from Redwood Shores. Several pump stations in the Redwood Shores system pump into this force main, and the change in hydraulic gradeline may necessitate upgrades to those pump stations. These potential upgrades are not addressed in this Master Plan report because they are related to the anticipated changes that will be implemented by SVCW on their facilities.1 3.3 SUMMARY OF SYSTEM FLOWS Table 3-3 summarizes the dry and wet weather flows in the Redwood City sewer system based on the hydraulic modeling results. Table 3-3:Summary of Wastewater Collection System Flows Model Scenario1 Maple St. Pump Station2 (mgd) Redwood Shores (mgd) Seaport/Pacific Shores (portion)3 (mgd) Existing Sewer Network Existing Average Dry Weather Flow 6.4 1.2 0.1 Existing Peak Dry Weather Flow 9.9 1.9 0.3 Existing Peak Wet Weather Flow4 38.6 5.6 1.1 Future Average Dry Weather Flow 9.7 2.1 0.1 Future Peak Dry Weather Flow 15.0 3.2 0.3 Future Peak Wet Weather Flow4 43.0 6.6 1.1 Future Sewer Network5 Future Peak Wet Weather Flow 47.1 7.0 1.1 1.Dry weather flow includes BWF plus wet season GWI; peak wet weather flow based on 10-year design storm event. 2.Main City area flow (including County SMDs tributary to Redwood City collection system) plus the portion of flow from Seaport/Pacific Shores that is tributary to Maple St. PS. 3.Portion of flow from Seaport/Pacific Shores that discharges directly to SVCW conveyance system. 4.Peak flows in existing sewer network may be reduced due to attenuation from upstream pipe capacity limitations and flow volume lost in model-predicted overflows. 5.With capacity improvement projects implemented. 1 The SVCW upgrades include raising the elevation of the headworks intake elevation 15.29 feet from its current elevation. Woodard & Curran completed a separate analysis of the Redwood Shores pump stations and force mains that would be affected by this change. The 10-year design storm flow was used for this analysis because it represents the minimum level of flow required to be conveyed to avoid overflows in the City’s system. For the scenario that was modeled, it was found that once the headworks intake is raised 15.29 feet, PS 17 will not be able to supply enough pressure to convey its flow into the common force main that conveys flow from Redwood Shores to the SVCW treatment plant. This could result in overflows in Redwood City’s system at or upstream of PS 17. ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 147 of 317