2014-028 - Approving General Plan Amendement No. 2014-01

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City of Santa Ana -Park View at Town and Country Manor Noise Draft OR Many methods have been developed for evaluating community noise to account for, among other things: • Variation in noise levels over time. • Influence of periodic individual loud events. • Community response to changes in the community noise environment. Numerous methods have been developed to measure sound over time, including: • Equivalent Sound Level (Leq). • Community Noise Equivalent Level (CNEL). • Day/Night Average Sound Level (L &). These methods are described and defined below. Equivalent Sound Level - L•q Time variations in noise exposure are typically expressed in terms of a steady -state energy level equal to the energy content of the time- varying period (called Leq), or, alternately, as a statistical description of the sound pressure level that is exceeded over some fraction of a given observation period. For example, the noise levels exceeded on 10 percent of readings is called Leo, the median (50th percentile) reading is called LSO, etc. Community Noise Equivalent Level - CNEL Because community receptors are more sensitive to unwanted noise intrusion during the evening and at night, state law requires that, for planning purposes, an artificial dB increment penalty be added to quiet -time noise levels in a 24 -hour noise descriptor called CNEL. Day /Night Average Sound Level - Ld„ Another commonly used method is the day /night average level or L &. The L& is a measure of the 24- hour average noise level at a given location. It was adopted by the U.S. Environmental Protection Agency (EPA) for developing criteria for the evaluation of community noise exposure. It is based on a measure of the average noise level over a given time period call the Leq. The L& is calculated by averaging the Leq for each hour of the day at a given location after penalizing the sleeping hours (defined as 10:00 p.m. to 7:00 a.m.) by 10 dBA to account for the increased sensitivity of people to noises that occur at night. The maximum noise level recorded during a noise event is typically expressed as L... The sound level exceeded over a specified time can be expressed as Lo (e.g., Lvo, L5o, Ljo)_ L5o equals the level exceeded 50 percent of the time; 1,10 equals the level exceeded 10 percent of the time, etc. As previously mentioned, people respond to changes in sound pressure, which are measured on a noise scale in a logarithmic manner. In general, a 3 -dB change in sound pressure level is considered a 4.5 -2 Michael Brandman Associates H\Clievt(PN -Rn) 327b327WMDEMVB270030 Sec0 Noi�.