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Draft Environmental Impact Report Page IV.0-1 Forward Landfill Expansion C. NOISE This section describes the existing and likely future noise environments in the vicinity of the proposed Forward Landfill Expansion Project. It also addresses the project's conformity with the San Joaquin County General Plan and Noise Ordinance. Set ins Background To describe noise environments and to assess impacts on noise-sensitive areas, a frequency weighting measure, which simulates human perception, is commonly used. It has been found that A-weighting of sound levels best reflects the human ear's reduced sensitivity to low frequencies, and correlates well with human perceptions of the annoying aspects of noise. The A-weighted decibel scale (dBA)t is cited in most noise criteria. Decibels are logarithmic units that conveniently compare the wide range of sound intensities to which the human ear is sensitive. Table IV.0-1 identifies typical ranges of decibel levels for common sounds heard in the environment. Table IV.GI Typical Noise Levels Noise Level d( BA) Outdoor Activity Indoor Activity 90+ Gas lawn mower at 3 feet,jet flyover Rock Band at 1,000 feet 80-90 Diesel truck at 50 feet Loud television at 3 feet 70-80 Gas lawn mower at 100 feet, noisy Garbage disposal at 3 feet,vacuum urban area cleaner at 10 feet 60-70 Commercial area Normal speech at 3 feet 40-60 Quiet urban daytime, traffic at 300 Large business office,dishwasher feet next room 20-40 Quiet rural, suburban nighttime Concert hall(background),library, bedroom at night 10-20 Broadcast / recording studio 0 Lowest threshold of human hearing Lowest threshold of human hearing Source: (modified from Caltrans Technical Noise Supplement,1998) Several time-averaged scales represent noise environments and consequences of human activities. The most commonly used noise descriptors are the equivalent A-weighted sound level over a given time 1 A decibel (dB) is a unit of sound energy intensity. Sound waves, traveling outward from a source, exert a sound pressure level (commonly called"sound level")measured in dB. An A—weighted decibel (dBA)is a decibel corrected for the variation in frequency response to the typical human car at commonly encountered noise levels.