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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Noise ■ Day-Night Level(Ld,). The energy average of the A-weighted sound levels occurring during a 24-hour period,with a 10-dB penalty added to the A- weighted sound levels occurring between 10:00 p.m. and 7:00 a.m. _ Under controlled conditions in an acoustical laboratory,the trained,healthy human ear is able to discern 1-dB changes in sound levels,when exposed to steady, single-frequency("pure-tone")signals in the mid-frequency(1,000 Hertz [Hz]to 8,000 Hz)range. However, it is widely accepted that people are able to begin to detect sound level increases of 3 dB,for typical noisy environments. Further,a 10-dB increase is generally perceived as a doubling of loudness. Therefore,doubling sound energy(e.g.,doubling the volume of traffic on a highway)generally would be perceived as a detectable,but not substantial, increase in sound level. — Environmental Setting - Surrounding Noise-Sensitive Land Uses _ The study area described in this section includes the quarry and measurement and prediction sites shown in Figure 3.J-1. The area surrounding the proposed project site is primarily agricultural. Active mining sites exist to the south and west of the proposed site. Nearby residences are located to the north of the project site,adjacent to SR 132. One residence is located near the proposed entrance to the DeSilva facility on Koster Road. One residence is located to the — west of the proposed facility between I-5 and the Delta-Mendota Canal. All residences in the study area are considered noise-sensitive. Existing Noise Environment Noise Monitoring In order to characterize the existing noise environment in the project study area, unattended noise monitors were installed at three locations in the project area vicinity for seven days. The long-term monitoring was supplemented by attended short-term measurements in the study area. — Jones & Stokes selected the noise monitoring sites to document existing ambient noise levels at representative noise-sensitive land uses in the project area. — Additionally, the sites were selected to provide reference locations for the assessment of Project-related noise impacts. The noise monitoring sites are described below: — Long-Term Noise Monitoring Noise monitoring equipment consisted of Larson-Davis Laboratories Model LD _ 700 sound level meters(serial numbers 1406, 1132, and 0190). The instrumentation was calibrated prior to use with a Larson Davis Model CA250 DeSilva Gates Quarry Project -- Draft Environmental Impact Report 3.J-2 Ms 05105.05