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Recommended Capacity Improvement Plan City of Redwood City (0011239.02)4-7 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 •Flow or project verification. As documented in Table 4-1, some of the capacity projects identified either had no flow meter specifically along the deficient reach to directly confirm the flow, or the model results indicated surcharging that has not been visually observed in the system. In these cases, the City may wish to conduct additional investigation to further verify the project need and sizing. Verification could be conducted by temporary flow or surcharge monitoring during wet weather periods. •Assessment of rehabilitation effectiveness. If the City conducts extensive repairs and rehabilitation within a relatively small area with a well-defined drainage area, conducting flow monitoring both before and after the rehabilitation efforts could provide valuable insight into how effective the rehabilitation has been in reducing RDI/I. If rehabilitation efforts are less concentrated, however, with work in various areas around the City, or if the drainage area is not well defined, with potential flow splits affecting flow coming into the basin, limited monitoring to try to assess rehabilitation effectiveness is not likely to be informative. In this scenario, the City would be better served by conducting periodic system-wide flow monitoring (perhaps every five years) in conjunction with a model calibration update to update RDI/I parameters. •Confirmation of flow prior to major developments. On occasion, it may be appropriate for the City to conduct temporary monitoring to verify flows in a pipe that is expected to be affected by a major development. Such monitoring is typically brief (2 to 3 weeks) and focused on dry weather capacity. •Model calibration update. The City will be relying on the new, all-pipe model developed for this Master Plan for a number of purposes. Periodically updating the model loads and the model calibration as populations and businesses change and as the City’s rehabilitation and repair efforts continue will be important for the model to continue to be useful in the future. For the purpose of keeping the model up-to-date, periodic system-wide flow monitoring is far more effective and provides a much sounder basis for updating the model calibration than limited annual monitoring. In selecting appropriate flow monitoring locations, both the accuracy of the collected data and the purpose of the monitoring need to be considered. For data accuracy, the best sites will have good hydraulics and be easily accessible (to facilitate field calibration and checking of meters). Although it is not always possible depending on the goals of the flow monitoring program, for the most accurate flow readings sites should generally avoid locations with sharp changes in pipe alignment or flow direction (such as 90-degree bends); manholes likely to have turbulent flow due to drops or junctions with multiple pipes; manholes with significant changes in pipe slope between the incoming and outgoing pipes; very shallow flow (e.g., less than 2 inches); very slow or very fast flow (less than 1 fps or more than 5 fps); backwater or surcharged conditions; sites impacted by backup or discharge from a pump station; and sites that experience significant grease, silt, sediment, or debris buildup. An effective approach to select sites with the best hydraulics possible is to first identify where sites are needed to serve the intended purpose of monitoring. Then review the sewer network data in the vicinity to identify what appears to be the best specific manhole for metering, but also determine how far upstream or downstream of this site the meter could be installed and still capture the flow intended. This way, if the selected site does not look ideal upon site investigation, the flow monitoring contractor can further investigate upstream or downstream to identify a manhole that would provide more suitable hydraulic conditions. Any flow monitoring conducted during wet weather needs reliable rainfall data to be useful. If there are no local, reliable rain gauges available, temporary rain gauge(s) should be installed as part of the flow monitoring program. ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 161 of 317