AgdaPkt 2010-01-25 clsd and regular

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6.2A Page 41 Impact NOI-lb: Nighttime pipeline construction activities would result in a substantial temporary increase in existing ambient noise levels in the Project vicinity. Preliminarily, three trenchless crossings and two open-trench crossings would be completed using continuous construction (24-hours per day) or nighttime-only construction, depending on the conditions of local jurisdiction encroachment permits, which may impose nighttime work to avoid daytime traffic impacts. Sensitive receptors (residential and school uses) are located in proximity to all five proposed locations with setback distances ranging from 10 to 140 feet. Potential noise increases associated with nighttime construction are presented in Draft EIR Table 4.12 16. Operation of heavy equipment (including pile drivers) in the vicinity of all crossing/pit locations would exceed the 50 dBA sleep interference criterion by up to 59 dBA (Le., potentially reach up to 109 dBA), resulting in a significant noise impact. . Mitigation Measure NOI-Ja: Noise Control Measures Impact NOI-lb would be partially mitigated through the actions described in Mitigation Measure NOI-la However, because it is unknown whether all affected residents will agree to relocation, the effectiveness of this mitigation measure cannot be determined at this time and therefore, this impact could remain significant and unavoidable. Impact NOI-lc: Construction of valve vaults, control buildings, and backup power facilities would result in a substantial temporary increase in existing ambient noise levels in the Project vicinity. Construction of new valve vaults, control buildings, and backup-power facilities would occur during the daytitne hours (consistent with time limits set by local noise ordinances) at valve lots located along the proposed Project alignnlent. Construction is expected to occur for approximately six months at each location, although it would not be continuous over this entire period. 'Worst-case noise estimates, based on minimum distances to residential receptors are presented in Table 4.12-13. In general, construction noise at the proposed valve vault locations without the use of sound attenuation devices would exceed. the 70 dBA speech interference criterion by up to 21 dBA at residential receptors. Construction would occur at distances of 100 feet or less from receptors at four locations: Driscoll Road Flow Meter Vault, Hayward Fault Crossing East Valve Vault, Hayward Fault Crossing West Valve Vault, and the Redwood City Valve Vault. Sensitive receptors would also be subject to noise fronl backup alarms. However, operation of heavy equipment at these four locations would be sporadic (e.g., occurring for approximately 3 to 5 days for drilling pile holes) and interspersed with periods when heavy equipment would not be operated within distances of 100 feet or less of any given adjacent sensitive receptor. Such factors could reduce adverse effects of construction noise at these locations. However, noise impacts from construction of these facilities could still be significant because of the proximity of sensitive receptors combined with the overall duration of construction tasks. ''':.' :'Mitigatioli'Meiis'iire NOI~la:"NoiseControIMeastires' Impact NOI-1c would be partially mitigated through the actions described in Mitigation Measure NOI-la. However, residents within 85 feet of the Driscoll Road Flow-Metering Vault and within 110 feet of the Hayward Fault Valve Lot West may still be exposed to temporary Project noise levels exceeding the 70 dBA indoor speech interference criterion. Therefore, at these locations, this impact would remain significant and unavoidable. Impact NOI..ld: Nighttime construction at the Ravenswood tunnel shaft site would result in a substantial temporary increase in existing ambient noise levels. 31