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5.7 Noise <br /> This section presents an assessment of potential noise effects related to the Lodi Energy <br /> Center (LEC). Section 5.7.1 discusses the fundamentals of acoustics. Section 5.7.2 describes <br /> the affected environment,including baseline noise level survey methodology and results. <br /> Section 5.7.3 presents an environmental analysis of the construction and operation of the <br /> power plant and associated facilities.Section 5.7.4 discusses cumulative effects. Section 5.7.5 <br /> discusses mitigation measures. Section 5.7.6 presents applicable laws, ordinances, <br /> regulations, and standards (LORS). Section 5.7.7 presents agency contacts,permit <br /> requirements,and permit schedules.Section 5.7.8 provides the references used to prepare <br /> this section. <br /> 5.7.1 Fundamentals of Acoustics <br /> Acoustics is the study of sound, and noise is defined as unwanted sound. Airborne sound is <br /> a rapid fluctuation or oscillation of air pressure above and below atmospheric pressure <br /> creating a sound wave. Acoustical terms used in this section are summarized in Table 5.7-1. <br /> The most common metric is the overall A-weighted sound level measurement that has been <br /> adopted by regulatory bodies worldwide. The A-weighting network measures sound in a <br /> similar fashion to the way in which a person perceives or hears sound. In this way,it <br /> provides a good measure for evaluating acceptable and unacceptable sound levels. <br /> A-weighted sound levels are typically measured or presented as equivalent sound pressure <br /> level (Leq),which is defined as the average noise level, on an equal energy basis for a stated <br /> period of time, and is commonly used to measure steady-state sound or noise that is usually <br /> dominant. Statistical methods are used to capture the dynamics of a changing acoustical <br /> environment. Statistical measurements are typically denoted by Lam,where xx represents the <br /> percentile of time the sound level is exceeded. The L90 is a measurement that represents the <br /> noise level that is exceeded during 90 percent of the measurement period. Similarly, the Lio <br /> represents the noise level exceeded for 10 percent of the measurement period. <br /> Some metrics used in determining the impact of environmental noise consider the <br /> differences in response that people have to daytime and nighttime noise levels. During the <br /> nighttime, exterior background noises are generally lower than the daytime levels. <br /> However,most household noise also decreases at night and exterior noise becomes more <br /> noticeable. Furthermore,most people sleep at night and are sensitive to intrusive noises. To <br /> account for human sensitivity to nighttime noise levels,the Day-Night Sound Level (Ldn or <br /> DNL) was developed. Ldn is a noise index that accounts for the greater annoyance of noise <br /> during the nighttime hours. <br /> Ldn values are calculated by averaging hourly Leq sound levels for a 24-hour period,and <br /> apply a weighting factor to nighttime Leq values. The weighting factor,which reflects the <br /> increased sensitivity to noise during nighttime hours,is added to each hourly Leq sound <br /> level before the 24-hour Ldn is calculated. For the purposes of assessing noise,the 24-hour <br /> day is divided into two time periods,with the following weightings: <br /> • Daytime: 7 a.m. to 10 p.m. (15 hours) Weighting factor of 0 decibels (dB) <br /> • Nighttime: 10 p.m. to 7 a.m. (9 hours) Weighting factor of 10 dB <br /> SAC/371322/08234009(LEC_5.7_NOISE.DOC) 5.7-1 <br />