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ARROYO LAGO RESIDENTIAL PROJECT ADDENDUM 140 FCS Https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480036/Addendum/21480036 Arroyo Lago Residential Project Addendum.docx located within a Flood Hazard Zone A, which represents an area with a 1 percent annual chance flood hazard. Additionally, the Prior FEIR noted that these facilities would be designed in accordance with applicable flood control and drainage standards, including provisions for safe conveyance of storm flows during extreme events through controlled overland release features that follow historic drainage patterns. The Arroyo Lago Off-site Utility Flood Study, prepared by Schaaf and Wheeler, dated March 13, 2024, indicates that the off-site improvements would not be inundated during a 100-year storm event because it is unlikely that the 100-year water surface elevation would be above ground at the location for the off-site improvements and that any spills that occur from the nearby lakes would be contained into the quarry ponds. Additionally, the water storage and booster pump facility would be designed in accordance with FEMA-published guidelines for development occurring within a 100-year Flood Hazard Zone. The WWTP and other infrastructure would be constructed above inundation zone elevations. Compliance with applicable FEMA standards and RWQCB Basin Plan requirements would ensure protection from flood-related pollutant release. The project site is located immediately south of Lake I of the Zone 7 Chain of Lakes, which could be susceptible to a seiche. However, the County Project would comply with all applicable regulations and requirements from the ECAP, Municipal Code, and NPDES to ensure protection from flood-related pollutant release. Additionally, the project site is approximately 16.4 miles east of the San Francisco Bay and 35.7 miles east of the Pacific Ocean. The project site would not be at risk of inundation from a tsunami. Therefore, the Prior FEIR concluded that impacts would be less than significant. (Draft EIR, pp. 3.9-32, 6-16). Proposed Project Analysis and Conclusion Similar to the conclusions of the Prior FEIR, the project site is approximately 16.4 miles east of the San Francisco Bay and 35.7 miles east of the Pacific Ocean. Given this distance from the ocean, the project site would not be at risk of inundation from a tsunami. As discussed in the Prior FEIR, the project site is located immediately south of Lake I of the Zone 7 Chain of Lakes, which could be susceptible to a seiche. However, the proposed project would comply with all applicable regulations and requirements from the City’s General Plan, Municipal Code, and NPDES, which would allow for the adequate sizing of storm drainage systems, preserve areas with percolation abilities, and minimize sedimentation and erosion. Therefore, consistent with the impact conclusions in the Prior FEIR, impacts related to a tsunami and inundation from a seiche would be less than significant. As also evaluated at length in the Prior FEIR, potential pollutants stored on-site during construction would be stored in a manner consistent with the proposed project’s NPDES-mandated SWPPP, as well as applicable regulations including, without limitation, those by OSHA, Department of Hazardous Substances and Materials, which help to prevent pollutant release.