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Less than Significant Impact with Mitigation Incorporation. A Noise Study Report (URS Corporation, 2007) was conducted to assess the noise impact of the proposed project on the surrounding community. The primary existing noise source in the area is South Harbor Boulevard, which borders the east side of the project site. The project is proposed in an existing commercial area surrounded by commercial developments, multi-family residences, mobile home park, and single-family residences. Mobile noise sources in the area consist of motor vehicle noise including automobiles, trucks, buses, and motorcycles. The noise produced by these sources occur primarily on South Harbor Boulevard and may be of sufficient magnitude to expose various land uses to excessive noise levels. Stationary noise sources in the area include equipment and operation of surrounding commercial land uses, noise from air conditioner units, pool and spa equipment, stereo and amplified music equipment, children, and domestic animals from nearby residences. "Noise" is defined as unwanted sound and is measured using the decibel (dB) scale. Additionally, the "A"-weighted sound level, dBA, is a "filter" or adjustment curve applied by the measuring instrument to shape the frequency content of the sound in a manner similar to the way the human ear responds to sounds. A change of 1 dBA is very difficult to perceive except in the laboratory. In the outside environment, a 3 dBA change is considered just perceptible, while an increase of 5 dBA is considered readily perceptible and would generally result in a change in community response. Finally, a 10 dBA increase is perceived as a doubling in loudness and would likely result in a widespread community response. The City of Santa Ana has adopted standards and guidelines for specific noise levels associated with various land uses. These guidelines are listed in Table 5, where the desired maximum noise value along with the acceptable maximum noise values for each land use category is shown. Table 5 -Ambient Noise Exposure Level Guidelines Noise Level (dBA CNEL or DNL) Land Use Desirable Maximum Ma~mum Acce table Residential -Low Densi 55 65 Residential -Medium Densit 60 65 Residential - Hi h Densit 65 70 Schools 60 70 Commercial Office 65 75 Industrial 70 75 Source: Noise Stud Re ort, URS Co oration. Febru 2007. Table 6 shows the daytime and nighttime guidelines for ambient noise levels, which the entire city is designated as Zone 1 by ordinance. 53 Initial Study/Mitigated Negative Declaration July 2008 ' Harbor Medical and Retail Center 7 5A 8 6