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4 Environmental Analysis 4.10 Hydrology/Water Quality within and away from the Project site, and this in turn could introduce contaminants and other pollution into surrounding waterways. However, compliance with the NPDES Construction General Permit and associated SWPPP and BMPs would reduce the potential for these impacts to occur. The Project site is not in a mapped flood zone, which further reduces the potential for impacts from flooding, or impeding or redirecting flood flows at the Project site.Adherence to the discussed federal and state laws would ensure the impacts are temporary and less than significant. Operations All of the earthwork occurs during the construction phase, so operating and maintaining Project facilities would not include any additional activities that could alter the existing drainage patterns at the Project site. The Project configuration would not create situations in which surface materials would be subject to erosion and subsequent sediment transport. A potential increase in impervious surface area of 18.8 acres represents a 2.4 percent change within the Project drainage area. The small size of the drainage areas on the Project site and the lack of identified flood zones eliminates the potential for impeding or exacerbating flooding. As a result, O&M of the Project are not expected to create any of the following conditions: � Cause substantial erosion and sedimentation on- or off-site; � Substantially increase surface runoff resulting in flooding on- or off-site; � Cause runoff water to exceed stormwater drainage system capacity or increase polluted runoff; or oo Change flood flows. Decommissioning Decommissioning the Project facility would include ground disturbing activities similar to those performed during construction, which may alter the drainage patterns at the Project site. The same requirements of the Construction General Permit and other applicable construction mitigation measures would apply to activities during decommissioning, and adherence to those requirements would reduce any potential impacts. Impacts during O&M and decommissioning would be temporary and less than significant. Mitigation: GEO-1 and HYDRO-1. IMPACT 4.10-4: Is the project in flood hazard, tsunami, or seiche zones, risk release of pollutants due to the project inundation? (No Impact) The Project site is not within a 100-year flood zone nor a dam inundation zone, according to the FEMA Flood Insurance Rate Map (FEMA 2009)and the Alameda County Local Hazard Mitigation Plan (Alameda County 2021). Additionally, the Project site sits above 300 feet of elevation and is separated from the San Pablo Bay(which is the closest estuarine waterbody to the Pacific Ocean) by at least 31 miles of Sacramento River channel stretching up to the Delta, and another 22 miles of overland distance. The closest large body of water is the Clifton Court Forebay, approximately 8 miles to the north and very near sea level elevation itself. Based on these conditions, the Project site is not at risk of inundation by a tsunami or seiche. There also would be no impact regarding the release of pollutants due to Project inundation. Griffith Energy Storage Project 4.10-16 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023