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' BENDER READY -MIX CONCRETE MANUFACTURING PROJECT
<br />Initial Study /Mitigated Negative Declaration
<br />4.12 NOISE
<br />Ll
<br />J
<br />Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air, and is
<br />characterized by both its amplitude and frequency (or pitch). The human ear does not hear all frequencies equally.
<br />In particular, the ear deemphasizes low and very high frequencies. To better approximate the sensitivity of human
<br />hearing, the A- weighted decibel scale (dBA) has been developed. On this scale, the human range of hearing
<br />extends from approximately three dBA to around 140 dBA.
<br />' Noise is generally defined as unwanted or excessive sound, which can vary in intensity by over one million times
<br />within the range of human hearing; therefore, a logarithmic scale, known as the decibel scale (dB), is used to quantify
<br />sound intensity. Noise can be generated by a number of sources, including mobile sources such as automobiles,
<br />trucks, and airplanes, and stationary sources such as construction sites, machinery, and industrial operations. Noise
<br />generated by mobile sources typically attenuates (is reduced) at a rate between three dBA and 4.5 dBA per doubling
<br />of distance. The rate depends on the ground surface and the number or type of objects between the noise source
<br />and the receiver. Hard and flat surfaces, such as concrete or asphalt, have an attenuation rate of three dBA per
<br />doubling of distance. Soft surfaces, such as uneven or vegetated terrain, have an attenuation rate of about 4.5 dBA
<br />per doubling of distance. Noise generated by stationary sources typically attenuates at a rate between six dBA and
<br />about 7.5 dBA per doubling of distance.
<br />There are a number of metrics used to characterize community noise exposure, which fluctuate constantly over time.
<br />' One such metric, the equivalent sound level (L q), represents a constant sound that, over the specified period, has
<br />the same sound energy as the time - varying sound. Noise exposure over a longer period of time is often evaluated
<br />based on the Day -Night Sound Level (Ld,), This is a measure of 24 -hour noise levels that incorporates a 10 -dBA
<br />' penalty for sounds occurring between 10:00 PM and 7:00 AM The penalty is intended to reflect the increased human
<br />sensitivity to noises occurring during nighttime hours, particularly at times when people are sleeping and there are
<br />lower ambient noise conditions. Typical Ld, noise levels for light and medium density residential areas range from 55
<br />dBA to 65 dBA.
<br />JULY 2011 4.12 -1 NOISE
<br />31A-75
<br />Less Than
<br />Wot�i'd the. pro/ecf
<br />Potentsal
<br />Sigdlficint
<br />Less Than
<br />SlgmticiM
<br />Impact With
<br />Significant
<br />No
<br />Impact
<br />Mit[ga6on
<br />Impact
<br />Impact
<br />InCorpor8ted
<br />a. Exposure of persons to or generation of noise levels in
<br />excess of standards established in the local general plan or
<br />✓
<br />noise ordinance, or applicable standards of other agencies?
<br />b. Exposure of persons to or generation of excessive
<br />groundborne vibration or groundborne noise levels?
<br />✓
<br />c. A substantial permanent increase in ambient noise levels in
<br />the project vicinity above levels existing without the project?
<br />✓
<br />d. A substantial temporary or periodic increase in ambient noise
<br />levels in the project vicinity above levels existing without the
<br />✓
<br />project?
<br />e. For a project located within an airport land use plan or, where
<br />such a plan has not been adopted, within two miles of a
<br />public airport or public use airport, would the project expose
<br />✓
<br />people residing or working in the project area to excessive
<br />noise levels?
<br />f. For a project within the vicinity of a private airstrip, would the
<br />project expose people residing or working in the project area
<br />✓
<br />to excessive noise levels?
<br />Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air, and is
<br />characterized by both its amplitude and frequency (or pitch). The human ear does not hear all frequencies equally.
<br />In particular, the ear deemphasizes low and very high frequencies. To better approximate the sensitivity of human
<br />hearing, the A- weighted decibel scale (dBA) has been developed. On this scale, the human range of hearing
<br />extends from approximately three dBA to around 140 dBA.
<br />' Noise is generally defined as unwanted or excessive sound, which can vary in intensity by over one million times
<br />within the range of human hearing; therefore, a logarithmic scale, known as the decibel scale (dB), is used to quantify
<br />sound intensity. Noise can be generated by a number of sources, including mobile sources such as automobiles,
<br />trucks, and airplanes, and stationary sources such as construction sites, machinery, and industrial operations. Noise
<br />generated by mobile sources typically attenuates (is reduced) at a rate between three dBA and 4.5 dBA per doubling
<br />of distance. The rate depends on the ground surface and the number or type of objects between the noise source
<br />and the receiver. Hard and flat surfaces, such as concrete or asphalt, have an attenuation rate of three dBA per
<br />doubling of distance. Soft surfaces, such as uneven or vegetated terrain, have an attenuation rate of about 4.5 dBA
<br />per doubling of distance. Noise generated by stationary sources typically attenuates at a rate between six dBA and
<br />about 7.5 dBA per doubling of distance.
<br />There are a number of metrics used to characterize community noise exposure, which fluctuate constantly over time.
<br />' One such metric, the equivalent sound level (L q), represents a constant sound that, over the specified period, has
<br />the same sound energy as the time - varying sound. Noise exposure over a longer period of time is often evaluated
<br />based on the Day -Night Sound Level (Ld,), This is a measure of 24 -hour noise levels that incorporates a 10 -dBA
<br />' penalty for sounds occurring between 10:00 PM and 7:00 AM The penalty is intended to reflect the increased human
<br />sensitivity to noises occurring during nighttime hours, particularly at times when people are sleeping and there are
<br />lower ambient noise conditions. Typical Ld, noise levels for light and medium density residential areas range from 55
<br />dBA to 65 dBA.
<br />JULY 2011 4.12 -1 NOISE
<br />31A-75
<br />
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