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4 Environmental Analysis 4.10 Hydrology/Water Quality 4.10 HYDROLOGY AND WATER QUALITY This section identifies and evaluates issues related to hydrology and water quality in the context of the Griffith Energy Storage Project (Project). The Project site includes the proposed facility and the generation tie (gen-tie) line corridor (including both the Applicant portion and the portion for which Pacific Gas and Electric [PG&E] will be responsible). The discussion below includes the physical and regulatory setting, the criteria used to evaluate the significance of potential impacts, the methods used in evaluating these impacts, and the results of the impact assessment for hydrology and water quality issues. The County received comments from the Central Valley Regional Water Quality Control Board and Federal Emergency Management Agency (FEMA) during the scoping period (the comment letter is included in Appendix A) and those comments have been incorporated into this section. 4.10.1 Existing Conditions The Project facility is to be located in western San Joaquin County along the border with Alameda County. The gen-tie line corridor extends into Alameda County from the proposed facility. This location is in the foothills near the junction of the northwestern San Joaquin Valley and the Sacramento-San Joaquin Delta. 4.10.1.1 Regional Setting and Climate The Project lies on the eastern flank of the Diablo Range of the Coastal Ranges Geomorphic Province and is very close to the adjoining Central Valley Geomorphic Province. The topography of the area is rolling hills that generally slope east toward the San Joaquin Valley. However, there is a prominent topographic high point (greater than 500 feet in elevation) on the eastern third of the Project site, midway between the north and south site boundaries. Two other lesser high points are located in the southwestern quadrant of the Project (426 feet in elevation) and in the northwestern quadrant (380 feet in elevation). The climate in the Project vicinity is Mediterranean, with wet winters and hot, dry summers. Climate data from the Tracy, California, weather station is representative of the local climate. The average maximum temperature varies from a winter low of 56 degrees Fahrenheit (°F) in January to a summer high of 93 degrees Fahrenheit in July. The average minimum temperature ranges from a winter low value of 37°F in January to a summer high value of 56°F in August. Rain- producing storms that occur over the Project site generally come from the west, deriving their moisture from the Pacific Ocean, before passing over the San Francisco Bay and the Diablo Range. Precipitation averages at locations west of the Diablo Range tend to be greater than those to the east. Thus, average annual precipitation in Berkeley (27 inches), Oakland (24 inches), and Walnut Creek (25 inches) are greater than Livermore (15 inches) or Tracy (13 inches), with the Project site located between the latter two locations (WorldClimate 2022). 4.10.1.2 Surface Water Hydrology The Project site is located within the sixth-level U.S. Geological Survey hydrologic unit identified as the Lower Old River sub-watershed (Hydrologic Unit Code [HUC] 180400030605), which is also within the San Joaquin River Basin. This sub-watershed covers an area of 1,232 square miles. The local drainage area, which contains the Project site, is relatively small, and consists of three unnamed channels that are tributary to the Sacramento-San Joaquin Delta. The Delta is a Griffith Energy Storage Project 4.10-1 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023