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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Noise 3.J Noise Introduction This section describes existing noise sources in the project area;presents the federal, state, and local policies and regulations that determine mitigation requirements; and identifies impacts associated with implementation of the proposed Project. Potential impacts of project alternatives on noise are described and analyzed in Chapter 4,"Alternatives Analysis." The key sources of data and information used in the preparation of this section are listed below. ` ■ County of San Joaquin Noise Ordinance, Chapter 9-1025.9 of the County Code(or County Development Title Performance Standards) ■ San Joaquin County General Plan,Public Health and Safety, Section D,page V-10 through V-11, July 1992 ■ Draft Noise Control Plan DeSilva Gates Quarry Project prepared by Bollard ►� Acoustical Consultants—July 26, 2006(copy provided in Appendix N) Background information on environmental acoustics, including definitions of �. terms commonly used in noise analysis,is provided in Appendix H. The following are brief definitions of terminology used in this chapter: ■ Sound. A vibratory disturbance created by a vibrating object,which, when transmitted by pressure waves through a medium such as air, is capable of being detected by a receiving mechanism, such as the human ear or a microphone. ■ Noise. Sound that is loud,unpleasant,unexpected,or otherwise undesirable. ■ Decibel(dB). A unitless measure of sound. A sound level measurement in decibels describes the logarithmic ratio of a sound pressure level to a reference sound pressure level,which is 20 micropascals. _ ■ A-Weighted Decibel(dBA). An overall frequency-weighted sound level that approximates the frequency response of the human ear. ■ Exceedance Sound Level(LJ. The sound level exceeded XX%of the time .. during a sound level measurement period. For example 1-90 is the sound level exceed 90%of the time and L10 is the sound level exceeded 10%of the time. ■ Maximum and Minimum Sound Levels(L„,.and L„id. The maximum or minimum sound level measured during a measurement period. ■ Equivalent Sound Level(Leq). Leq represents an average of the sound energy occurring over a specified period. In effect, Leq is the steady-state sound ` level containing the same acoustical energy as the time-varying sound that actually occurs during the same period. DeSilva Gales Quarry Project Draft Environmental Impact Report 3.J-1 As 05105.05