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4.6 NOISE 't j INTRODUCTION # This section examines specific noise impacts related to the proposed mining and processing of aggregates. Definitions of acoustical terms used below are presented in t Section 7.4 of this EIR. Unless otherwise stated, all sound levels are reported in terms of A-weighted sound pressure levels, in decibels (dB). A-weighting de-emphasizes very low and very high frequencies of sound in a manner similar to the human ear. Most community E noise standards utilize A-weighting, as it provides a high degree of correlation with human !R annoyance and health effects. I� SETTING {� Existing Ambient Noise Environment l t The existing noise environment in the project vicinity is defined primarily by distant traffic on Interstate 5 and local farming operations. To quantify existing ambient noise levels in { the project vicinity a continuous noise level measurement survey was conducted at two j locations on March 12, 1997. The noise measurement sites, which are shown on Figure r 4.6-1, generally represent the locations of the two nearest residential uses to the project site. i Larson Davis Laboratories (LDL) model-700 integrating sound level meters were used for I� the ambient noise level measurement survey. The meters were calibrated before and after use with a LDL CA-250 acoustical calibrator to ensure the accuracy of the measurements. The equipment used meets pertinent American National Standards Institute (ANSI) specifications for precision sound level measurement instrumentation. The results of the IF ambient noise level measurement survey are shown numerically in Table 4.6-1 and a graphically on Figures 4.6-2 and 4.6-3. i� The Table 4.6-1 data indicate that existing average ambient noise levels range from the l ' mid 40's to low 50's dB Leq, with maximum noise levels-in the high 60's dB Lmax for Site A and mid 70's db Lmax for Site B. The computed values of Ld„were 51 and 57 dB at the monitoring sites. Site B had a direct line of site to Interstate 5, which accounts for the II higher noise levels than measured at Site A, which was primarily affected by local farm- Draft traffic. r d !I f x > E Draft Environmental Impact Report 4-83 x ER-96-3 i _ II