AgdaPkt 2010-01-25 clsd and regular

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6.2A Page 43 In addition to increased noise in the tunnel shaft vicinity, there would be a short-term noise increase north of the shaft when the SFPUC's pipeline is connected to the Alameda County Water District pipeline and when grout injection pipes are installed. Construction-related noise levels at the center would exceed the 60 dBA significance threshold. Therefore, because much of this equipment would need to be operated at night - ventilation fans are required at all times that workers are underground, which would be up to 24-hours a day, cranes would be operated at night to raise and lower workers as necessary, and pumps would be operated as often as necessary (up to 24-hours per day) to maintain dry working conditions underground - resulting noise levels would represent a significant and unavoidable noise impact on nearby sensitive receptor (including captive wildlife). . Mitigation Measure NO/-Ia: Noise Control Measures . Mitigation Measure NO/-Ib: Construction Contract Specifications Impact NOI-le would be partiaIJy mitigated through the actions described in Mitigation Measure NOI-la as well as Mitigation Measure NOI-lb. However, residential receptors with direct line of sight to the shaft construction and associated nighttime construction activities could still occasionally be exposed to an exceedance of the 50 dBA sleep interference criterion, with the Ohlone Humane Society Wildlife Rehabilitation Center being occasionally exposed to an exceedance of the 60 dBA criterion. Impact NOI-lf: Noise disturbance from helicopter operations could result in a substantial temporary increase in existing ambient noise levels in the Project vicinity, depending on helicopter ffight patterns, helicopter type, and flight altitude. As part of the Project-related upgrades to existing PG&E facilities, PG&E would install a fiber optic cable between the Ravenswood and Ames Substations. Because these towers are located in coastal marsh and waters, a helicopter would be required to transport the cable, equipment, and construction personnel to each tower location. Since helicopter activity would progress along the cable alignment, exposure of any particular residential receptor would be less than two weeks. However, since specific flight paths and landing areas are yet to be developed, a potential for disturbance to nearby residential receptors remains. In addition, the type of helicopter used by the contractor could be quieter or louder than the type of helicopter assumed in this analysis. Therefore, because of these uncertainties and potential variations, helicopter noise disturbance could result in a significant impact. . Mitigation Measure NO/-Ie: Helicopter Noise Control Measures Implementation of Mitigation Measure NOI-Ic, helicopter noise control nleasures, would reduce potential noise disturbance impacts from helicopter operations. As flight paths are developed, a qualified acoustical consultant must be retained to assess potentially affected noise sensitive receptors and provide recommendations, as part of Mitigation Measure NOI-Ic, which if feasible . . ~~;~~~i~i~~1~1~h~~~se;~ri6W.~J~rif:~.~citW~f~~m~~~~tr6:\h~~6iJeeI;n~iict~&el~\~~lh~h~.. . significant levels, it may remain significant and unavoidable. Impact NOI-lg: Daytime truck and vehicle traffic increases on the Ravenswood Valve Lot access road during tunnel construction and staging would create a substantial temporary increase in ambient noise levels in the project vicinity. Based on traffic estimates, tunnel construction at the Ravenswood Valve Lot would generate an average of 150 truck trips and 160 worker vehicle trips to and from the construction site per clay, or up to a maximum of 20 truck trips and 65 worker vehicle trips during the Project's peak traffic generation hour. Based on these maximum hourly volumes and FHW A noise-modeling 33