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Capacity and I/I Assessment City of Redwood City (0011239.02)3-2 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 design rainfall event. This Master Plan sets the timing of the design storm rainfall such that the peak RDI/I resulting from the design storm occurs at or near the time of peak BWF for most areas of the system, as shown in Figure 3-1. It should be noted that for its 2021 Draft Sewer Master Plan for the Fair Oaks SMD, the County has adopted the same design storm criteria as Redwood City. This ensures that the basis of the capacity assessment for City sewers that convey Fair Oaks SMD flows will be consistent with the rest of the system. Future scenarios were modeled conservatively under the assumption that the sewer system’s response to rainfall would remain the same as existing conditions. This assumption implies that any increase in I/I due to deterioration of existing sewers will be offset by a decrease due to sewer rehabilitation or replacement, and that new sewers and laterals will contribute minimal I/I flows. While I/I flows will likely decrease in the future as a result of the City’s on-going sewer rehabilitation efforts, it is not possible at this time to quantify these reductions or anticipate where they will occur. However, if confirmed by flow monitoring, results from future sewer rehabilitation programs could be incorporated into the rainfall response assumptions for future model updates. Figure 3-1:Design Rainfall Event (Central Redwood City) 3.1.2 Capacity Deficiency Criteria Capacity deficiency or performance criteria are used to determine when the capacity of a sewer pipeline or pumping facility is exceeded to the extent that a capacity improvement project (e.g., a relief sewer, larger replacement sewer, or pump station capacity expansion) is required. Capacity deficiency criteria are sometimes called “trigger” criteria in that they trigger the need for a capacity improvement project. These criteria may differ from “design criteria” that are applied to determine the size of a new facility, which may be more conservative than the performance criteria. ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 137 of 317