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Executive Summary City of Redwood City (0011239.02)6 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 RECOMMENDED CAPACITY IMPROVEMENT PROGRAM The capacity improvement program recommended in this study is designed to provide adequate sewer system capacity for the City’s existing and anticipated future development. Figure ES-3 and Figure ES-4 show the locations of the proposed capacity improvements projects. As shown in the figures, most of the projects are located in the Main City collection system. The recommended improvement projects are listed in Table ES-2. For the most part, the sewer capacity improvement projects involve replacing existing deficient sewers with larger diameter pipes. Note that eight of the 25 gravity sewer capacity improvement projects were also identified as being needed in the City’s previous master plans (although recommended pipe sizes or the exact extent of the projects may have differed slightly). The other projects are primarily on small diameter sewers that were not previously included in the trunk system model used in the previous studies. Note also that all or a portion of five of the capacity improvement projects identified in the City’s 2008 master plan have been completed since that study; however, a number of others were found to be no longer needed based on the updated modeling conducted for this study. Since most of the proposed capacity improvement projects are driven by wet weather flows due to high I/I, an evaluation was conducted to identify the potential for eliminating (or substantially reducing) needed capacity relief projects through reduction in RDI/I flows. Based on an assumed 30 percent reduction in RDI/I (considered to be reasonably achievable through comprehensive rehabilitation of sewer mainlines and lower laterals), it was determined that eight projects could potentially be eliminated or reduced in size through this level of I/I reduction. These results suggest possible areas of focus for future flow monitoring and sewer rehabilitation efforts. However, results should be confirmed by post- rehabilitation flow monitoring before the projects are removed from the capacity improvement program. The total estimated capital cost of the capacity improvement program is approximately $42 million, as shown in Table ES-3. For gravity sewers, these cost estimates include baseline construction costs for gravity trunk sewers using open- cut and trenchless methods, lower lateral replacement for remove-and-replace projects, and cost allowances for project mobilization and demobilization, traffic control, and bypass pumping. The total estimated capital costs also include a 30 percent allowance for contingencies for unknown conditions and an allowance of 25 percent of construction cost for engineering, administration, construction management, and legal costs. The estimated costs are conceptual level estimates and are considered to have an estimated accuracy range of -30 to +50 percent. These estimates are considered suitable for use for budget forecasting, CIP development, and project evaluations, with the understanding that refinements to the project details and estimated costs would be necessary as projects proceed into the design and construction phases. All costs are presented in 2023 dollars. ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 95 of 317