Reso25 16341 - Laserfiche WebLink

Browse Search

City of Redwood City (0011239.02)4-1 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 4.RECOMMENDED CAPACITY IMPROVEMENT PLAN This chapter describes the recommended plan for capacity improvements, including estimated costs and priorities for implementation. The chapter also provides general recommendations for implementation of the capacity improvement program. 4.1 CAPACITY IMPROVEMENT PROGRAM As presented in Chapter 3, capacity improvement projects were identified to address the potential deficiencies identified through the hydraulic modeling. Each project is documented in further detail in Appendix D with an individual plan map and project information sheet that provides project details, key considerations, and a planning-level capital cost estimate. For each project, the construction method (open cut or pipe bursting) was assumed based on the proposed pipe diameters and depths in order to estimate costs; however, the actual construction method should be confirmed during design based on project-specific conditions. 4.1.1 Cost Criteria Costs for capacity improvement projects were estimated based on Woodard & Curran’s experience with similar projects in the greater San Francisco Bay Area, as well as bid information from other projects constructed by the City and nearby agencies. These cost estimates are conceptual level estimates and are considered to have an estimated accuracy range of -30 to +50 percent. This level of accuracy corresponds to an “order of magnitude” or “Class 5” cost estimate as defined by the American Association of Cost Estimators. These estimates are suitable for use for budget forecasting, capital improvement program development, and project evaluations, with the understanding that refinements to the project details and costs would be necessary as projects proceed into the design and construction phases. Cost estimates for the capacity improvement projects were originally developed in 2021; however, all costs have been adjusted to an Engineering News Record Construction Cost Index (ENR CCI) of 15,370, which represents the July 2023 ENR CCI for the San Francisco Area. Cost criteria include baseline unit construction costs for gravity sewers using open-cut and trenchless (e.g., pipe bursting) methods. Costs for gravity trunk sewers vary with pipe diameter and depth (in the case of open-cut construction) and include an allowance for lower lateral replacement. Allowances added to the baseline construction cost include mobilization/demobilization and project-specific costs for bypass pumping, traffic control, and delay factor for remove-and-replace construction. A 30 percent allowance for contingencies for unknown conditions was also included for all projects, as well as an allowance of 25 percent of construction cost for engineering, administration, construction management and legal costs. Detailed cost estimates for all of the capacity improvement projects are provided in Appendix D. 4.1.2 Project Rankings and Flow Confirmation Levels For gravity sewer capacity improvements, project rankings were developed based on two factors; design storm deficiency level and flow confirmation level. The design storm deficiency level reflects the extent of model-predicted surcharge (or potential overflow) under design storm PWWF. Four deficiency levels were defined, as follows: 1.Model-predicted overflow 2.Model-predicted surcharging within 3 feet of ground 3.Model-predicted surcharging within 5 feet of ground 4.Model-predicted surcharging within 5 feet of ground only under future conditions ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 155 of 317