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3.4 Noise is reduced to approximately 89 percent if the proposed haul truck noise exposure reduction F} parameters are applied;that is, if haul truck noise exposure is reduced by 4 dB using the proposed t operating parameters presented above. FProject Conditions Again,using ANSI/ASA 512.9-2008 Part 6 and the vehicle/haul truck operations assumption presented above,the probability of awakenings from combined operations of existing traffic and E proposed project haul trucks on East River Road in the project area was calculated to be approximately 100 percent. This probability is reduced to approximately 99 percent given the application of the haul truck noise exposure reduction parameters. Impacts and Mitigation Measures (7 Impact 3.4.1: Project asphalt plant operations would add to the noise environment in the project vicinity.This impact is less than significant. FAs described above,asphalt plant operations.(on-site noise sources)during the hours of 9 p.m. to 4� 5 a.m. would not be expected to produce noise exposure in excess of 43 dB Le,/Lm at the closest existing residential receivers to the north and east. This noise exposure level would not exceed the 'Y County's nighttime noise limits for outdoor activity areas of 45 dB hourly Leq and 65 dB Lm . Existing ambient noise exposure at the closest residences to the north of project site(represented �L by measurement site 4)was measured to be in the range of 51-63 dB hourly Leq.Project asphalt plant operations would generally be more than 10 dB below the existing ambient noise exposure and would not be expected to add significantly to the noise environment at these receivers.Existing ambient noise exposure at the closest residences to the east of the project site (represented by measurement site A)was measured to be in the range of 35-48 dB hourly LeQf with an average hourly L,of 43 dB during 9 p.m.to 5 a.m. hours. On average,project-related asphalt plant noise would be expected to add 2 dB to the noise environment at the closest residence to the east(site A).Given the relatively low ambient noise exposure at this location,a+5 dB threshold of significance is appropriate. Therefore, project-related noise exposure from on-site sources is not expected to !`r add significantly to the noise environment at the closest receiver locations to-the east of the • project site. Mitigation Measures: None required. I ! Impact 3.4.2: Off-site project haul truck traffic would add to the noise environment in the project vicinity.This impact is potentially significant. As presented above,project haul truck noise exposure would be expected to produce noise exposure of approximately 66 dB Ld„or 62 dB Ld„at the closest residences to the project site on East River Road(60 feet from the roadway centerline)when operated under-typical parameters or proposed optimized parameters,respectively.Assuming the typical truck operating parameters,project haul Munn&Perkins Quarry Excavation Permit 3.4-15 - ESA 1211086 . Draft EIR Apnl 2011