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I (g) BENDER READY-MIX CONCRETE MANUFACTURING PROJECT Initial Study/Mitigated Negative Declaration 1 4.12 NOISE Ll J Less Than Would the project: Potentially Significant Less Than Na Significant Impact With Significant Impact Impact Mitigation Impact Incorporated a. Exposure of persons to or generation of noise levels in excess of standards established in the local general plan or ? noise ordinance, or applicable standards of other agencies? b. Exposure of persons to or generation of excessive ? groundborne vibration or groundborne noise levels? c. A substantial permanent increase in ambient noise levels in the project vicinity above levels existing without the project? ? d. A substantial temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the ? project? e. For a project located within an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, would the project expose ? people residing or working in the project area to excessive noise levels? f. For a project within the vicinity of a private airstrip, would the project expose people residing or working in the project area ? to excessive noise levels? Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air, and is characterized by both its amplitude and frequency (or pitch). The human ear does not hear all frequencies equally. In particular, the ear deemphasizes low and very high frequencies. To better approximate the sensitivity of human hearing, the A-weighted decibel scale (dBA) has been developed. On this scale, the human range of hearing extends from approximately three dBA to around 140 dBA. ' Noise is generally defined as unwanted or excessive sound, which can vary in intensity by over one million times within the range of human hearing; therefore, a logarithmic scale, known as the decibel scale (dB), is used to quantify sound intensity. Noise can be generated by a number of sources, including mobile sources such as automobiles, trucks, and airplanes, and stationary sources such as construction sites, machinery, and industrial operations. Noise generated by mobile sources typically attenuates (is reduced) at a rate between three dBA and 4.5 dBA per doubling of distance. The rate depends on the ground surface and the number or type of objects between the noise source and the receiver. Hard and flat surfaces, such as concrete or asphalt, have an attenuation rate of three dBA per doubling of distance. Soft surfaces, such as uneven or vegetated terrain, have an attenuation rate of about 4.5 dBA per doubling of distance. Noise generated by stationary sources typically attenuates at a rate between six dBA and about 7.5 dBA per doubling of distance. There are a number of metrics used to characterize community noise exposure, which fluctuate constantly over time. ' One such metric, the equivalent sound level (L q), represents a constant sound that, over the specified period, has the same sound energy as the time-varying sound. Noise exposure over a longer period of time is often evaluated based on the Day-Night Sound Level (Ld,), This is a measure of 24-hour noise levels that incorporates a 10-dBA ' penalty for sounds occurring between 10:00 PM and 7:00 AM The penalty is intended to reflect the increased human sensitivity to noises occurring during nighttime hours, particularly at times when people are sleeping and there are lower ambient noise conditions. Typical Ld, noise levels for light and medium density residential areas range from 55 dBA to 65 dBA. JULY 2011 4.12-1 NOISE 31A-75