Construction noise levels at and near locations on the project sites would fluctuate depending on the particular type, number, and duration of use of various pieces of construction equipment. The effect of construction noise would depend upon how much noise would be generated by construction, the distance between construction activities and the nearest noise-sensitive receptors, and the existing noise levels at those sites.
The noisiest phases of construction would generate approximately 89 Leq at 50 feet (EPA, 1971). Construction activities would require the transportation of materials, equipment and supplies to the two sites. Noise emissions generated from construction equipment varies from 75 dBA for jack hammers to 90 dBA for front-end loaders and hydraulic equipment. Noise from localized construction point sources usually decrease by 6 dBA with each doubling of distance from source to receptor.
Under normal conditions PG&E construction crews work weekdays from 7:00 a.m. to 3:00 p.m. To maintain dryness in open vaults, an electric generator may be used during nighttime hours to operate air conditioning and a sump pump.
The sensitive noise receptors nearest to the proposed construction activity would be residences located on either side of the excavation alignment along Salem Avenue, Foothill Boulevard, Starling Avenue, Baxter Avenue, Creston Drive, and Groveland Drive. These roadways vary from 30 to 60 feet curb to curb. While the centerline of the alignment has not yet been determined, the distance between construction areas and residences will likely be less than 100 feet in many locations and result in noise levels above ambient conditions at some residences. Consequently, construction noise mitigation measures should be implemented. Excavation activity and reconductoring would be of short duration, lasting a day or two at any one location. Such temporary construction activity is permitted pursuant to Ordinance 26 of the City of Cupertino Municipal Code.
Daily access to the site and vehicle parking by construction workers is not anticipated to result in noticeable increases in noise levels for residents.
Since operation of the project would not result in long-term traffic increases, long-term noise impacts are not expected to occur. Additionally, the proposed project would not result in long-term operational source noise. Therefore, operation of the proposed project would result in less than significant noise impacts.
"Severe" noise levels are generally regarded as those that can produce hearing damage or other health effects. Typically, severe noise levels are associated with such activities as piledriving or blasting. The proposed project would not result in the types of activities that would produce severe noise levels. Motor vehicles do not produce "severe" noise levels, and while some construction equipment can produce "severe" levels, the potential health effects are limited to the geographic area in the immediate vicinity of the facility where the concern is for worker health (OSHA standards apply) rather than for members of the general public.
Applicant Proposed Mitigation
The following measures have been proposed by PG&E to reduce construction noise impacts to a less than significant level:
The location and sequencing of construction activities shall be coordinated with the City of Cupertino and Santa Clara County.
Compressors and other small stationary equipment will be shielded and equipment exhaust will face away from noise-sensitive buildings (residences and businesses).
Any generators operating during nighttime hours shall be noise insulated "super quiet" units emitting a noise level of approximately 48 dBA at a distance of 50 feet.
Existing natural and manmade features (e.g., landscaping, fences) will be used to shield construction noise whenever possible.
Regular equipment maintenance and mufflers will be required on all construction equipment to control noise
Vehicle idling time will be minimized (e.g., five minutes maximum), unless required for construction purposes.
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