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4 Environmental Analysis 4.13 Noise 4.13 NOISE This section identifies and evaluates issues related to noise in the context of the Griffith Energy Storage Project (Project). It 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. San Joaquin County (County) received no scoping comments regarding noise. 4.13.1 Existing Conditions The Project site is approximately 0.9 mile southwest of Interstate 580 and approximately 5 miles southwest of the city of Tracy, adjacent to the Pacific Gas and Electric (PG&E) Tesla Substation. The Project site is private land zoned as Agricultural General-160 and designated as General Agriculture. The site includes Grazing Land and Farmland of Local Importance, as classified by the California Department of Conservation. The nearest non-participating residential structure is approximately 0.2 mile southwest of the Project. 4.13.1.1 Acoustic Metrics and Terminology All sounds originate with a source, whether it is a human voice, motor vehicles on a roadway, or a combustion turbine. Energy is required to produce sound and this sound energy is transmitted through the air in the form of sound waves—tiny, quick oscillations of pressure just above and just below atmospheric pressure. These oscillations, or sound pressures, impinge on the ear, creating the sound we hear. A sound source is defined by a sound power level (abbreviated "Lw"), which is independent of any external factors. By definition, sound power is the rate at which acoustical energy is radiated outward and is expressed in units of watts. A source sound power level cannot be measured directly. It is calculated from measurements of sound intensity or sound pressure at a given distance from the source outside the acoustic and geometric near-field. A sound pressure level (abbreviated "LP") is a measure of the sound wave fluctuation at a given receiver location and can be obtained through the use of a microphone or calculated from information about the source sound power level and the surrounding environment. The sound pressure level in decibels (dB) is the logarithm of the ratio of the sound pressure of the source to the reference sound pressure of 20 micropascals (pPa), multiplied by 20. The range of sound pressure that can be detected by a person with normal hearing is very wide, ranging from about 20 pPa for very faint sounds at the threshold of hearing, to nearly 10 million pPa for extremely loud sounds, such as a jet during take-off at a distance of 300 feet. Broadband sound includes sound energy summed across the entire audible frequency spectrum. In addition to broadband sound pressure levels, analysis of the various frequency components of the sound spectrum can be completed to determine tonal characteristics. The unit of frequency is hertz (Hz), measuring the cycles per second of the sound pressure waves. Typically, the frequency analysis examines 11 octave bands ranging from 16 Hz (low) to 16,000 Hz (high). Since the human ear does not perceive every frequency with equal loudness, spectrally varying sounds are often adjusted with a weighting filter. The A-weighted filter is applied to compensate for the frequency response of the human auditory system and is represented in A-weighted decibel (dBA). Griffith Energy Storage Project 4.13-1 Tetra Tech/2022120675 Draft Environmental Impact Report August 2023