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' B. Exposure of persons to or generation of excessive groundborne vibration or groundborne noise levels? ' Less than Significant Impact with Mitigation Incorporation. As previously mentioned above, 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. Therefore, the proposed project as mitigated will not produce excessive groundborne vibration or groundborne noise levels. Refer to response in Noise (A.), above. Implementation of mitigation ' measures, as mentioned in Noise (A.), above, would reduce impacts to less than significant levels. ' C. A substantial permanent increase in ambient noise levels in the project vicinity above levels existing without the project? Less than Significant Impact with Mitigation Incorporation. The proposed project involves the construction and operation of commercial building with retail, restaurant, and medical-office uses. The proposed project will result in the ' increase in noise associated with the day-to-day activities of a typical commercial building including increases in vehicular traffic along roadways, an increase in noise levels associated with mechanical operation of the building, and noise from i vehicles accessing and maneuvering through the parking facility. However, as mentioned above, the projected increase in traffic volumes associated with the proposed project represents an increase in noise of approximately 0.1 dB CNEL and imperceptible to most people. Mitigated noise levels from the mechanical equipment proposed for the project is expected to be less than the measured ambient noise level at the project site and less than the daytime noise ordinance level of 55 dBA Ley at all sensitive noise receptors adjacent to the proposed project site. Noise associated with the parking facility will be reduced with the existing 6 feet wall and would not exceed the noise values and time durations of the City of Santa Ana Noise Ordinance. Refer to response in Noise (A.), above. ' D. A substantial temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the project? Less than Significant Impact with Mitigation Incorporation. Refer to response ' in Noise (A.), above. ' S9 Initial Study/Mitigated Negative Declaration July 2008 ' Harbor Medical and Retail Center ~ ~ w ^