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4 Environmental Analysis 4.10 Hydrology/Water Quality 4.10.4 Impact Analysis IMPACT 4.10-1: Would the project violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface or groundwater quality? (Less than Significant with Mitigation Incorporated) Construction Parts of the Project site will require a considerable volume of earthwork. However, these activities would occur in remote portions of two watersheds, and runoff management would be limited to the areas of disturbance. Concerns for water"run-on" from a larger watershed are not applicable to this Project site. Construction would involve the use of bulldozers, graders, semi-trucks, and various other types of heavy equipment for vegetation removal, grubbing, grading, and installation of roads and other facilities. Construction activities would involve significant changes to onsite topography, and such activities could potentially loosen existing surface soils and sediments, increasing the possibility that erosion might occur during storm events. Water used for dust suppression also has the potential to generate runoff that could transport sediments and dissolved solids. The use of construction equipment onsite may involve the accidental release of fuel, oils, brake dust, lubricants, antifreeze, and other potentially hazardous substances at the Project construction site. These water quality pollutants could be delivered to surface waterbodies during storm events, and/or be infiltrated into groundwater and the underlying aquifer, resulting in the degradation of water quality. As a result of these concerns, the Project would be subject to compliance with the Construction General Permit, as described in Mitigation Measure GEO-1. The Construction General Permit would include development and implementation of a SWPPP. The objectives of a SWPPP are to identify pollutant sources that may be delivered offsite (in the form of runoff) and affect the quality of stormwater discharge; to implement site controls and practices to reduce stormwater pollution; and to protect water quality of receiving waters. The SWPPP would include site-specific BMPs to minimize erosion onsite and reduce or otherwise prevent conditions of erosion and stormwater runoff. As described in Section 4.9, Hazards and Hazardous Materials, diesel and gasoline fuels and other hazardous materials, such as oils, solvents, hydraulic fluids, and paints commonly associated with construction equipment, would be stored and handled in a manner to prevent accidental release (i.e., consistent with the hazardous materials handling BMPs, Spill Prevention, Control, and Countermeasure (SPCC) Plan, and other measures contained within the required SWPPP). By complying with General Construction Permit implementation requirements, which would include the preparation and deployment of a SWPPP, SPCC Plan, and associated BMPs, the impact on water quality during construction would be temporary and less than significant. Operations After the Project construction is completed and final stormwater management facilities are in place, control of runoff will maintain or improve the runoff conditions currently found at the site prior to construction. The average water use during operations and maintenance (O&M) of the battery energy storage system (BESS)facility would be minimal, estimated at close to zero acre- Griffith Energy Storage Project 4.10-12 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023