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u ~' Table 8 -Short Term Noise Measurement Data Site ID Location Leq (dBA) 520 South Harbor Boulevard, 50 feet west of west curb, 100 ST-1 feet north of south ro ert line. 69.7 520 South Harbor Boulevard, 50 feet west of west curb 50 ST-2 , feet south of north ro ert line. 68'8 520 South Harbor Boulevard, 250 feet west of west curb 10 ST-3 , 67 8 feet south of residential ro ert line. ' 520 Harbor Boulevard, 300 feet west of west curb 5 feet ST-4 , north of residential ro erty line. 53.5 Source: Noise Stud Re ort, URS Cor oration. Februar 2007. Construction Noise Construction of the proposed project will result in short-term increases in the ambient noise level. The magnitude of the increases would depend on the type of construction activity, the noise levels generated by the various pieces of construction equipment, the duration of the construction phase, and the distance between the noise source and receptors in the area. Noise levels generated by construction equipment generally decrease at a rate of approximately 6 dBA per doubling of distance from the source. As such, at a distance of 100 feet, the noise levels will be about 6 dBA lower than at the 50 foot reference distance and similarly, at a distance of 200 feet, the noise levels would be approximately 12 dBA lower than at the 50 foot reference distance. The subterranean parking facility will require extensive grading to accommodate the base of the parking facility 13 feet below the existing grade of the site. The southwest corner of the subterranean parking facility will be located approximately 10 feet from the property line of the adjacent single family residences. The proximity of the subterranean parking facility to the noise sensitive land uses presents the probability that noise and vibration will be experienced during the construction phase. Furthermore, piles will be required to provide structural support for the subterranean parking facility. As a substitute for pile driving, casings will be drilled into the foundation floor to accommodate the piles. This procedure results in significantly lower noise levels of 10 to 15 dB compared with traditional pile driving methods. With implementation of the following mitigation measures, limiting the hours of construction hours in accordance with local noise ordinances, and the temporary nature of construction, impacts from construction activities would be reduced to less than significant levels. Mitigation Measures NOI-1 Construction activities shall comply with the applicable local jurisdiction's construction noise requirements. The City of Santa Ana Noise Ordinance prohibits construction activities between the hours of 8:00 p.m. and 7:00 a.m. Monday through Saturday, anytime on Sundays, and federal holidays. 55 Initial Study/Mitigated Negative Declaration ' Harbor Medical and Retail Center ~ ~ w ~ Q Q July 2008