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are calculated on a logarithmic basis. An increase of 10 decibels represents a ten-fold increase in acoustic energy, while 20 decibels is 100 times more intense, 30 decibels is 1,000 times more intense, etc. There is a relationship between the subjective noisiness or loudness of a sound and its intensity. Each 10 decibel increase in sound level is perceived as approximately a doubling of loudness over a fairly wide range of intensities. Technical terms are defined in Table 1. TABLE 1 Definitions of Acoustical Terms Used in this Report Term Definition A unit describing,the amplitude of sound,equal to 20 times the logarithm to the Decibel, dB base 10 of the ratio of the pressure of the sound measured to the reference pressure. The reference pressure for air is 20. Sound pressure is the sound force per unit area,usually expressed in micro Pascals(or 20 micro Newtons per square meter), where I Pascal is the pressure resulting from a force of l Newton exerted over an area of 1 square meter. The Sound Pressure Level sound pressure level is expressed in decibels as 20 times the logarithm to the base 10 of the ratio between the pressures exerted by the sound to a reference sound pressure (e.g.,20 micro Pascals). Sound pressure level is the quantity that is directly measured by a sound level meter. The number of complete pressure fluctuations per second above and below Frequency, Hz atmospheric pressure. Normal human hearing is between 20 Hz and 20,000 Hz. Infrasonic sound are below 20 Hz and Ultrasonic sounds are above 20,000 Hz. The sound pressure level in decibels as measured on a sound level meter using the A-Weighted Sound A-weighting filter network. The A-weighting filter de-emphasizes the very low Level, dBA and very high frequency components of the sound in a manner similar to the frequency response of the human ear and correlates well with subjective reactions to noise, Equivalent Noise Level, L The average A-weighted noise level during the measurement period. The maximum and minimum A-weighted noise level during the measurement Lmax, Lmin period. The A-weighted noise levels that are exceeded 1%, 10%, 50%,and 90%of the Lot, Ltp, 1-50, L90 time during the measurement period. Day/Night Noise Level, The average A-weighted noise level during a 24-hour day,obtained after addition Ldn or DNL of 10 decibels to levels measured in the night between 10:00 pm and 7:00 am. Community Noise The average A-weighted noise level during a 24-hour day,obtained after addition Equivalent Level, of 5 decibels in the evening from 7:00 pm to 10:00 pm and after addition of 10 CNEL decibels to sound levels measured in the night between 10:00 pm and 7:00 am. The composite of noise from all sources near and far. The normal or existing Ambient Noise Level level of environmental noise at a given location. That noise which intrudes over and above the existing ambient noise at a given Intrusive location. The relative intrusiveness of a sound depends upon its amplitude, duration,frequency,and time of occurrence and tonal or informational content as well as the prevailing ambient noise level, Source: Handbook of Acoustical Measurements and Noise Control,Harris, 1998. There are several methods of characterizing sound. The most common method in California is the A-weighted sound level or dBA. This scale gives greater weight to the frequencies of sound to Page 4 J