2009-034 (2) - Final Supplemental Environmental Impact Report for Fairhaven/Lincoln

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S. Environmental A nalysis NOISE • om u ity Noise Equivalent Level 111EL). The energy average of the A- weighted hte occurring during a 24 -Jour period with d6 9 9 � sound bevels p added to the sound levels occurring during the period from 7 Phi to 10 P M and 10 dB added to the sound levels occurring durir the period from 7 A1. 9 R 1 PM to L.d, and CNEL values rarely differ by more than 1 dB. As a matter of practice, and NEL considered to bee equivalent and are treated �, values are q eated as such �r� this assessment, Eloise Descriptors Noise i s most often defined as unwan ed sound, Although soun d can be easily measured, the erne ticn noise and the physical response to sound complicate the anal P p of p +s of its impact an popre, People fudge the relative magnitude of sound sensation in subjective terms such as "noisiness" or "loudness." Characteristics of Sound When are object vibrates, it radiates part of its energy as acoustical pressure in the form of a sound wave. Sound can be described in terms of amplitude (loudness), frequency (pitch), or duration (time). The human hearing system is not equally sensitive to sound at all frequencies. Therefore, to appro orate this human frequency - dependent response, the - weighted filter system is used to adjust measured sound levels. The normal range of human hearing extends from approximately 0 dBA to 140 dB A. Unlike linear units such as inches or pounds, decibels are measured on a logarithmic scale, representing points on a sharply rising curve. Because of the physical characteristics of noise transmission and noise perception, the relative loudness of sound does not closely match the actual amounts of sound energy. Table ,2 -1, Change in Sound Pressure Level, Presents the subjective effect of chap levels. � gas �n sound pressure Table 5.2-1 Chan a in Sound Pressure ILevel lra a in Apparent Loudness ± 3 dB Threshold of human perceptibility ± 5 dB Cleanly nofteable change in noise level 10 dB Half or trice as laud ± 0 dB Much quieter or ruder Source. Bies and Hansen 2003 Bound is generated from a source and dissipates exponentially with distance from that source. When sound is measured for distinct time intervals, the statistical distri bution of the overall sound level durin that eriod can be obtained. The sound level equivalent L is the most cone 9 p g �� commonly the parameter associated with such measurements. L,,, is the average sound level over a given period of time. For example, the L.50 noise level is the level that is exceeded 50 percent of the time; half the time the noise exceeds this level and half the time it is less than this level. This level is also exceeded 30 minutes in an hour. Similarly, the L-02, L ,,and L values are the noise levels that are exceeded 2, 8, and 25 percent of the time or 1, 3, and 15 minutes per Dour. Other values typically noted during a noise survey are the and P �,�� L. These are the minimum and maximum noise levels obtained over the measurement period. Page 5.2-2 he Planning Venter Resolution No. 2009 -034 Page 68 of 130 March 2009