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Draft Supplemental Environmental Impact Report Page IV.0-5 Forward Inc. Landfill 2018 Expansion Project A residential structure (9690 Austin Road) is also along Austin Road approximately 1,300 feet south- southeast of the northeast expansion area. It is directly east of the Forward Landfill main entrance. However,this structure is currently vacant and lacking electricity and plumbing, and so cannot be occupied at this time. Impacts Impact significance under CEQA is evaluated relative to the existing environment. For the purposes of this analysis,the"existing noise environment"is the current noise environment,which includes the existing operational conditions at the landfill(i.e.,approximately 233 trucks per day). This section ' includes a summary of impacts and mitigations considered in the 2013 EIR,and has been updated to include impacts and mitigations that are new or have been substantially altered by changes in the proposed project. To facilitate review of the section and comparison of analyses between the 2013 EIR ' and this document,the heading for each impact or mitigation measure reflects whether that impact is the same, revised, replaced, or new. ' Standards of Significance Under ambient conditions, most people cannot distinguish a change in the noise environment that differs by less than 3 dBA between the pre-and post-project exposure. A clearly perceptible increase in noise level differences occurs around+5 dBA. The operational noise impact studies prepared for the 1993, 1994,2000, and 2002 EIRs for the Forward and Austin Road landfills adopted a+5 dBA increase ' as a significant noise impact. Subsequent to those studies, ambient levels in the area have increased. For the purposes of this analysis, the noise impact from any new landfill traffic would be potentially significant if it would increase exterior noise levels by at least 5 dBA or more at any of the nearby ' residential land uses that are currently at or below the County's maximum allowable Ldn noise exposure level of 65 dBA for transportation sources(see Table IV.0-2). ' As discussed in the 2013 EIR, the existing elevated traffic noise levels related to landfill and other existing truck traffic in the area already exceed the County's maximum allowable exposure level of 65 dBA Ldn along several road segments in the project areas. Like the 2013 EIR,this SEIR applies an adjustable threshold based on absolute noise level. When existing exterior noise levels are more than 65 dBA Ldn at a residential receptor, the threshold would be an increase of 3 dBA. This adjustable threshold is a methodology based on a federal noise study of neighborhood annoyance related to airports that has been used extensively in California in City and County Noise Elements for assessing the effects of highway transportation noise levels (FICON, 1992). ' Impact C.I. Construction Noise Impacts (Revises 2013 EIR Impact C.1.) Temporary construction noise would result during site preparation activities for the project, such as the proposed creek relocation and preparation of the proposed expansion areas. Noise levels associated with such activities would be short-term and would be similar to the equipment noise levels that are already occurring at the landfill. Such activities would not substantially affect existing noise levels in the vicinity of the project and would have no effect on the long-term noise exposure in the project vicinity.