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2021 Multijurisdictional Local Hazard Mitigation Plan Toxic Release Inventory Reporting Facilities Toxic Release Inventory (TRI) facilities are known to manufacture, process, store, or otherwise use certain chemicals above minimum thresholds. If damaged by a flood, these facilities could release chemicals that cause cancer or other human health effects, significant adverse acute human health effects, or significant adverse environmental effects (U.S. Environmental Protection Agency, 2021). During a flood event, containers holding these materials can rupture and leak into the surrounding area, disastrously affecting the environment and community members. One facility within the 1-percent-annual-chance flood zone is a TRI reporting facility. Roads The following major roads within the planning area pass through the 1-percent-annual-chance flood zone (100- year floodplain), and thus are exposed to flooding:  State Highway 1  State Highway 82  State Highway 84  State Highway 92  State Highway 109  State Highway 114  US Highway 101  Interstate 380 Some of these roads were built above the flood level, and others function as levees to prevent flooding. Still, during severe flood events, these roads can be blocked or damaged, preventing access to some areas. Bridges Flooding events can significantly impact road bridges, important because many provide the only ingress and egress to some neighborhoods. An analysis indicated that 62 bridges are within or cross over the 1-percent- annual-chance flood zone (100-year floodplain). Levees Historically, levees have been used to control flooding in portions of San Mateo County. The County constructed levees both for flood protection (in the north and central portions of the County) and for salt evaporation ponds (in the southeast portion of the County). The County does not believe these levees could withstand intensities of a 1- percent-annual-chance flood. Additionally, coastal flooding from San Francisco Bay circumvents levees near the Bay, leading to flooding within the residential area next to San Francisquito Creek on the east side of the City. These risk estimates are based on current flood levels and do not account for potential sea level rise, which would exacerbate vulnerability and even further reduce ability of the levees to prevent/control flooding. Details on San Mateo County levees could not be supplemented by the U.S. Army Corps of Engineers National Levee Database. Although the database contains records of the majority of levees within the Corps’ system, it does not include records of all levees in the United States, which include the levees in San Mateo County. Levee failures could place large numbers of people and great amounts of property at risk. Unlike dams, levees do not serve any purpose beyond providing flood protection and (less frequently) recreational space for community members. A levee failure could be devastating, depending on severity of flooding and amount of land development present. In addition to damaging buildings, infrastructure, trees, and other large objects, levee failure can result in significant water quality and debris disposal issues. Severe erosion is also a consideration. 11-22