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4 Environmental Analysis 4.13 Noise 4.13.3 Thresholds of Significance The following thresholds of significance are based on Appendix G of the CEQA Guidelines. The proposed Project would have a significant impact to noise if it would: a) Result in generation of a substantial temporary or permanent increase in ambient noise levels in the vicinity of the project in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies; b) Result in generation of excessive groundborne vibration or groundborne noise levels; c) For a project within the vicinity of a private airstrip or an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, expose people residing or working in the project area to excessive noise levels. 4.13.4 Impact Analysis IMPACT 4.13-1: Would the project result in generation of a substantial temporary or permanent increase in ambient noise levels in the vicinity of the project in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies? (Less than Significant Impact with Mitigation Incorporated) Construction The Acoustical Analysis Report (Appendix F) estimated the noise levels generated by the Project during each stage of construction. Acoustic emission levels for activities associated with Project construction were based on typical ranges of energy equivalent noise levels at construction sites, as documented by the USEPA (1971) and the USEPA's Construction Noise Control Technology Initiatives (1980). The USEPA methodology distinguishes between type of construction and construction stage. The basic model assumed spherical wave divergence from a point source located at the center of the Project site to each receptor structure. Furthermore, the model conservatively assumed that all pieces of construction equipment associated with an activity would operate simultaneously for the duration of that activity. An additional level of conservatism was built into the construction noise model by excluding potential shielding effects due to intervening structures and buildings along the propagation path from the site to receiver locations. The construction processes are anticipated to occur during a period of approximately 15 months and begin in 2024. Project construction would generally consist of five major stages. The first stage would include mobilization, site preparation, fencing, and laydown. The second stage would involve excavation, trenching, and trench backfill. The medium-voltage stations would sit on concrete foundations or driven piles, pending final design. The construction noise analysis conservatively assumes pile driving will be required for this activity as part of the second stage. Pile driving would be the worst-case option in terms of noise as opposed to using concrete foundations. The third stage includes installation of cables and utilities. The fourth stage includes construction and installation of the battery storage units, and also includes commissioning and testing.. The final stage includes road paving. Table 4.13-5 summarizes the proposed equipment to be used for each stage and the associated noise level of the equipment. Table 4.13-6 summarizes the received construction noise levels at each NSA. Griffith Energy Storage Project 4.13-9 Tetra Tech/2022120675 Draft Environmental Impact Report August 2023