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Significance After Mitigation: Dispersion modeling shows that the California ambient air quality standard for Hydrogen Sulfide would not be exceeded. The use of additives in the AC mix should reduce the odor associated with rubberized AC production. However, based on previous complaints, it cannot be demonstrated that all odor impacts to receptors within one mile would be reduced to the point where no future complaints would be received. Therefore, the impact is identified as significant and unavoidable. Noise Significant project-related noise exposure would occur if the project stationary noise sources (e.g., asphalt plant) exceed the County's nighttime limit of 45 dB hourly Leq or the nighttime maximum 65 dB Lmax at off-site outdoor activity areas. Also, a significant impact would occur if noise from proposed project haul truck operations would exceed the applicable County noise exposure limits of 65 dB Lde (exterior) or 45 dB La„ (interior). Development Title Section 9-1025.9 Nighttime Operations Existing ambient noise exposure at the closest residences to the north of project site 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 was measured to be in the range of 35-48 dB hourly Leq, with an average hourly Leq 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. As described above, asphalt plant operations (on-site noise sources) during the hours of 9 p.m. to 5 a.m. would not be expected to produce noise exposure in excess of 43 dB Leq/Lmax at the closest existing residential receivers to the north and east. This noise exposure level would not exceed the County's nighttime noise limits for outdoor activity areas of 45 dB hourly Leq and 65 dB Lmax. Therefore, project-related noise exposure from on-site sources is not expected to add significantly to the noise environment at the closest receiver locations to the east of the project site. Impact : Project asphalt plant operations would add to the noise environment in the project vicinity. This impact is less than significant. Mitigation Measures: None required. On and Off-site Haul Truck Movement(Noise) Project-related noise exposure from the haul truck movements (on and off-site) would affect nearby residential receivers between the hours of 9:00 p.m. and 5:00 a.m. The increase in noise exposure is potentially significant based on the increase in ambient noise and the potential for sleep disturbance associated with periodic noise. A given truck passby was assumed to produce an average event noise exposure level of 58 dB SEL within a residence 60 feet from the centerline of the roadway (83 dB exterior SEL) (SEL-the equivalent sound level over a 1-second time interval for a discrete sound event i.e truck passby). For single-event noise, the probability of awakenings due to project haul truck operations on East River Road was calculated to be approximately 89-93 percent for residences 60 feet from the centerline of the roadway. The lower probability (89 percent) is related to the application of proposed optimized truck operating parameters, with the upper probability (93 percent) assuming typical operations. The probability of awakenings was calculated to be 99-100 percent when the cumulative effects of existing vehicle traffic and project haul trucks on East River Road are combined. The increase in probability of awakenings due to the project haul trucks was calculated to be 7-8 percent. This level of increase is considered significant. San Joaquin County QX-89-0002/Aggregates Inc. Community Development Page 7