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<br /> <br />Red Morton Community Park Sports Lighting Initial Study <br />City of Redwood City 53 June 2015 <br />4.12 NOISE <br /> <br />The following discussion is based upon the environmental noise assessment prepared for the <br />proposed project by Illingworth & Rodkin, Inc., noise consultants, in March 2015. This report is <br />included as Appendix B of this Initial Study. <br /> <br />4.12.1 Setting <br /> <br />Several factors influence sound as it is perceived by the human ear, including the actual level of <br />sound, the period of exposure to the sound, the frequencies involved, and fluctuation in the noise <br />level during exposure. Noise is measured on a “decibel” (dB) scale which serves as an index of <br />loudness. Because the human ear cannot hear all pitches or frequencies, sound levels are frequently <br />adjusted or weighted to correspond to human hearing. This adjusted unit is known as the “A- <br />weighted” decibel or dBA. Further, sound is averaged over time and penalties are added to the <br />average for noise that is generated during times that may be more disturbing to sensi tive uses such as <br />early morning or late evening. <br /> <br />Since excessive noise levels can adversely affect human activities (such as conversation and <br />sleeping) and human health, federal, state, and local governmental agencies have set forth criteria or <br />planning goals to minimize or avoid these effects. The noise guidelines are almost always expressed <br />using one of several noise averaging methods such as Leq, DNL, or CNEL.24 <br /> <br />4.12.1.2 Regulatory Setting <br /> <br />Redwood City Noise Ordinance <br /> <br />Chapter 24 (Noise Regulation) of the Redwood City Municipal Code (the Noise Ordinance) sets <br />allowable noise limits for different types of receiving land uses. The noise levels allowed by the <br />Noise Ordinance depend primarily on the background noise level in the area. Section 24.20A <br />prohibits noise increases of six decibels above local ambient measured noise at any point within a <br />residential district due to an assembly of three or more people during the hours of 8:00 p.m. and 8:00 <br />a.m. Section 24.32 of the Noise Ordinance establishes that noise levels generated by construction are <br />prohibited between the hours of 8:00 p.m. and 7:00 a.m. weekdays, or at any time on Saturdays, <br />Sundays, and holidays. In addition, Section 24.31 of the Noise Ordinance prohibits noise levels from <br />exceeding 110 dBA for any item of machinery, equipment, or device used during construction in a <br />residential district. <br /> <br /> <br /> <br />24 Leq stands for the Noise Equivalent Level and is a measurement of the average energy level intensity of noise over <br />a given period of time such as the noisiest hour. DNL stands for Day-Night Level and is a 24-hour average of noise <br />levels, with 10 dB penalties applied to noise occurring between 10:00 PM and 7:00 AM. CNEL stands for <br />Community Noise Equivalent Level; it is similar to the DNL except that there is an additional five (5) dB penalty <br />applied to noise which occurs between 7:00 PM and 10:00 PM. Generally, where traffic noise predominates, the <br />CNEL and DNL are typically within two (2) dBA of the peak-hour Leq. <br />8.A. - Page 70