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Draft Environmental Impact Report Page IV.0-13 Forward Landfill Expansion Impacts Impact significance under CEQA is evaluated relative to the existing environment. For purposes of analysis,the "existing noise environment"is the current noise environment and already-permitted landfill expansion that was previously addressed in earlier CEQA documents, (i.e.,620 vehicles/day and disposal footprint of 354.5 acres). = Standards of Significance CEQA Guidelines identify significant impacts as those that cause standards to be exceeded where they are currently met. An impact is also considered significant if it "measurably"worsens an existing unacceptable noise environment. Impacts may also be significant if they "substantially" worsen noise exposures even if adopted standards are not exceeded. Measurable is not defined in any guidelines. 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. For purposes of this analysis, an increase of 5 dB that creates an area of noise/land use incompatibility or which worsens an existing excessive noise situation would be considered a significant degradation of noise quality. In addition,because of the existing elevated traffic noise levels related to landfill and other existing truck traffic in the area, this EIR uses an adjustable threshold based upon the existing absolute noise level. When existing noise levels are less-than 60 dBA, the threshold would continue to be 5.0 dBA; when existing noise levels are between 60 and 65 dBA, the threshold would be 3.0 dBA; and when existing noise levels are more than 65 dBA,the threshold would be 1.5 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 highway transportation noise levels (FICON, 1992). Impact C.1. Construction Noise Impacts. Temporary construction noise would result during site preparation activities for the project, such as the proposed creek relocation and installation of the proposed waste containment system. 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. Therefore, this impact would be less than significant. i Mitigation Measure C.I.None required. 1 Impact C.2. Truck Traffic Noise Impacts. The proposed project would generate an additional 680 daily truck trips(340 in/340 out). The landfill is currently permitted for up to 1,240 daily trips. This volume has been assumed as the existing baseline condition. Traffic projections were prepared for the project in June 2009,by Republic ITS. The noise analysis used the Federal Highway Administration Traffic Noise Model(FHWA TNM)LookUp Model Program,Software version 2.1,to estimate noise levels under five scenarios (i.e.,existing,existing plus project,existing plus project plus approved projects(cumulative),year 2035(cumulative)with no project, and year 2035 (cumulative)plus project) at the eight project area roadway segments throughout the project area that would be most affected by the project. The results are presented in Table IV.C4. { r