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<br />the United States Environmental Protection Agency, is a 24- <br />hour average sound level (similar to a 24-hour Leq) in <br />which a 10 dB penalty is added to the Leg occurring between <br />the hours of 10:00 PM and 7:00 AM. CNEL, which was <br />developed for use in the California Airport Noise <br />Regulations, is similar to the Ldn except that a five dB <br />penalty is also added for noise occurring during evening <br />hours from 7:00 PM to 10:00 PM. Therefore, both the L~ and <br />CNEL noise metrics provide 24-hour averages of A-weighted <br />noise levels at a particular location. The distinction is <br />that Ldn includes a nighttime adjustment while the CNEL <br />metric includes both an evening and a nighttime adjustment. <br />For noise generated from vehicle traffic, CNEL and Ldn can <br />be used interchangeably because noise levels would differ <br />between these two noise descriptors by less than one dB. <br /> <br />Stationary Source Noise Standards <br /> <br />The City of Santa Ana uses an hourly exterior noise <br />standard to regulate stationary sources of noise. This <br />hourly exterior noise standard has allowances for higher <br />noise levels that would occur for shorter time periods. <br />For example, the exterior noise level standard is set at 55 <br />dBA over 30 minutes of an hour. This means that 50% of the <br />noise levels measured in an hour can not exceed 55 dBA. The <br />corresponding noise statistic (Ln) for this is L50 which is <br />calculated by dividing 30 minutes over 60 minutes and shows <br />that noise level that is exceeded 50% of the time. Another <br />example is the 60 dBA exterior noise standard which is <br />allowed to occur for 15 minutes of a 60 minute hour or 25% <br />of the time (15 minutes divided by 60 minutes). Table N-l <br />below shows exterior stationary noise standards and their <br />corresponding Ln. <br /> <br />Noise <br /> <br />Table N-l <br />Standard and Correspond Ln <br />(dBA) <br />75 70 65 <br /> <br />60 <br /> <br />55 <br /> <br />City Maximum Exterior <br />Noise Standard <br /> <br />Time Allowed to Occur <br /> <br />Maximum 2 <br />minutes <br /> <br />Corresponding Ln <br /> <br />Maximum <br /> <br />L(2) <br /> <br />5 <br />minutes <br />L (8) <br /> <br />15 <br />minutes <br />L (25) <br /> <br />30 <br />minutes <br />L (50) <br /> <br />The City of Santa Ana Noise Regulation is provided in <br />Article 6 of the Municipal code. The standards address <br />both exterior and interior noise impacts. <br /> <br />20 <br /> <br />31A~51 <br />