Agmt21 Environmental Science Associates Transit District

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Proposed Work Program June 2021 City of Redwood City / Transit District Subsequent EIR 12 Environmental science associates REV: 06-22-21 MI 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. The models will be run with the City’s 30-year and 100-year design storm events. The peak flows in the system downstream of the project will identified for each event. These locations include the 27” RCP pipe northeast of the Caltrain tracks that drain to the Bradford pump station, and the 15’ x 5’ box culvert in Redwood Creek that drains under the Caltrain tracks. 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. The Transit District is located in an area that is currently flooded in a 100-year event. Therefore, the project 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 (2) are 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. 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.) An increase in construction under the Transit District may also result in an increase in construction-related sedimentation and pollutants in stormwater runoff and/or groundwater. The increase in new development as a result of the project may also change the amount of impervious surfaces and resultant surface runoff within the DTPP area, and thus increase pollutants in surface water, and/or interfere with groundwater recharge; ESA will work with the City to develop appropriate assumptions with respect to changes in impervious surface. These effects will be addressed in conjunction with a discussion of governing federal, State and local regulations and requirements (e.g., NPDES/SWPPP requirements, and local stormwater management programs and ordinances) that are in place to ensure potential short- and long-term hydrology and water quality impacts would be minimized. Noise and Vibration The DTPP Final EIR determined significant but mitigable impacts under the DTPP associated with construction related noise and vibration effects; new residential exposure to noise levels in excess of General Plan guidelines; and residential exposure to ground borne vibration within the vicinity of the Caltrain railroad tracks. Noise and vibration impacts of the Transit District will be evaluated in the SEIR. Generally, this analysis will address construction noise and vibration, operational traffic noise increases on local roadways, and stationary source noise from mechanical equipment and loading areas. Additionally, if requested by the City, the analysis will consider non-CEQA related impacts of the environment on the projects inclusive of noise and vibration from operation of the Caltrain rail line on proposed sensitive land use sites in the SEIR. ESA will collect short- term noise measurements in the DTPP area to re-establish existing conditions. ESA will describe the existing ATTY/AGR.2021.149/ESA (Transit District CEQA) (Page 22 of 26)