Agmt21 Environmental Science Associates

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Proposed Work Program June 2021 City of Redwood City / Gatekeeper Projects Subsequent EIR 13 environmental science associates by the City. It is assumed that this will involve an update to the future project list that was used for the Master Plan. The City will also provide the latest information on the land use types and quantities for the Transit District and Gatekeeper projects. Woodard & Curran will conduct a separate model run of the updated existing and baseline future scenarios with and without the Gatekeeper Projects. Based on the model run, Woodard & Curran will identify improvements needed to convey design peak flows under the existing and baseline future scenarios in accordance with the design flow and hydraulic criteria established in the Sewer Master Plan, and will identify any additional capacity improvements needed to convey project flows. Woodard & Curran will prepare a Technical Memorandum for the Gatekeeper Projects area, summarizing the methodology, assumptions, and results of the modeling. Comments received on the draft Memorandum will be incorporated into a final Technical Memorandum to support the CEQA analysis. Woodard & Curran will conduct normal project management activities, including monitoring budget and schedule and preparing monthly invoices and progress reports. Woodard & Curran will attend up to three (3) meetings or teleconferences related to this project. Stormwater (Wood Rogers) To assess the impacts of the proposed development to the storm drainage system, Wood Rodgers will modify the City’s calibrated Eastern Low-Lying Area (ELLA) existing storm drain model to reflect the changes in land use for 7 of the 15 projects. For the remaining 8 projects, the existing drainage system must be added to the models. Wood Rodgers will use the existing City GIS database, and supplement with as-builts only when necessary. Wood Rodgers will define the watersheds, the watershed parameters, and add to the ELLA model. The models will be run with the City’s 30-year and 100-year design storm events, and the peak flows in the system downstream of the project identified for each event. The local floodplains around and downstream from the project will be mapped for each event. These will be compared with the peak flows and the local floodplains for existing (pre-project) condition. The analysis and the impacts will be documented in a short technical memorandum. Few of the Gatekeeper projects are located in an area that is currently flooded in a 100-year event. Those projects will likely require flood protection features such as fill, and will require flood mitigation due to filling the existing floodplain in order to mitigate downstream impacts. The conceptual improvements will be modeled to assess their effectiveness. It is assumed that 1-2 conceptual improvements for each outfall will be necessary. Wood Rodgers will provide conceptual designs of necessary improvements to remove the floodplain and to mitigate the impacts of the removal. These improvements may include detention, diversions, or capacity improvements. The conceptual improvements necessary will be documented in the technical memorandum. It is assumed that none of these projects will have substantial impacts to peak flows downstream. Hydrology and Water Quality The DTPP Final EIR determined all hydrology and water quality impacts under the DTPP to less than significant. (Stormwater drainage impacts will be addressed under Utilities and Infrastructure, above. This section of the EIR will address effects related to water quality, groundwater recharge, flooding due to tsunami, seiche, and dam failure, and the potential for coastal flooding along San Francisco Bay.) REV: 06-23-21 MI ATTY/AGR.2021.150/Environmental Sciences Associates (Gatekeeper Projects) (Page 23 of 58)