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<br />Legacy Sunflower Apartments Page 69 <br />Mitigated Negative Declaration – March 14, 2019 <br /> <br />Mitigation Measure No. 5 The contractor shall locate equipment staging in areas that would create <br />the greatest distance between construction-related noise sources and <br />sensitive receptors nearest the project site during all project construction. <br /> <br />Mitigation Measure No. 6 Jackhammers, pneumatic equipment and all other portable stationary <br />noise sources shall be shielded and noise shall be directed away from <br />sensitive receptors. <br /> <br />Mitigation Measure No. 7 The project proponent shall mandate that the construction contractor <br />prohibit the use of music or sound amplification on the project site during <br />construction. <br /> <br />Mitigation Measure No. 8 The construction contractor shall limit haul truck deliveries to the same <br />hours specified for construction equipment. <br /> <br />Ambient Noise <br /> <br />Noise Fundamentals <br /> <br />Sound is a pressure wave created by a moving or vibrating source that travels through an elastic <br />medium such as air. Noise is defined as unwanted or objectionable sound. The effects of noise on <br />people can include general annoyance, interference with speech communication, sleep disturbance, <br />and in extreme circumstances, hearing impairment. <br /> <br />The unit of measurement used to describe a noise level is the decibel (dB). The human ear is not <br />equally sensitive to all frequencies within the sound spectrum. Therefore, the “A-weighted” noise scale, <br />which weights the frequencies to which humans are sensitive, is used for measurements. Noise levels <br />using A-weighted measurements are written dB(A) or dBA. <br /> <br />From the noise source to the receiver, noise changes both in level and frequency spectrum. The most <br />obvious is the decrease in noise as the distance from the source increases. The manner in which noise <br />reduces with distance depends on whether the source is a point or line source as well as ground <br />absorption, atmospheric effects and refraction, and shielding by natural and manmade features. Sound <br />from point sources, such as air conditioning condensers, radiates uniformly outward as it travels away <br />from the source in a spherical pattern. The noise drop-off rate associated with this geometric spreading <br />is 6 dBA per each doubling of the distance (dBA/DD). Transportation noise sources such as roadways <br />are typically analyzed as line sources, since at any given moment the receiver may be impacted by <br />noise from multiple vehicles at various locations along the roadway. Because of the geometry of a line <br />source, the noise drop-off rate associated with the geometric spreading of a line source is 3 dBA/DD. <br /> <br />Decibels are measured on a logarithmic scale, which quantifies sound intensity in a manner similar to <br />the Richter scale used for earthquake magnitudes. Thus, a doubling of the energy of a noise source, <br />such as a doubled traffic volume, would increase the noise levels by 3 dBA; halving of the energy would <br />result in a 3 dBA decrease. Figure 15 shows the relationship of various noise levels to commonly <br />experienced noise events. <br /> <br />Average noise levels over a period of minutes or hours are usually expressed as dBA Leq, or the <br />equivalent noise level for that period of time. For example, Leq(3) would represent a 3-hour average. <br />When no period is specified, a one-hour average is assumed. <br /> <br />6-91