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4 Environmental Analysis 4.13 Noise levels for transmission lines with wet conductors are shown in Table 4.13-7 and, as such, a noise level of 40 dBA was used for the transmission line in the noise model. Table 4.13-7. Estimated Transmission Line Noise AudibleLine Voltage . : 138 34 240 40 360 51 Broadband (dBA) sound pressure levels were calculated for expected normal Project operation assuming that all components identified previously are operating continuously and concurrently at the representative manufacturer-rated sound. The sound energy was then summed to determine the equivalent continuous A-weighted downwind sound pressure level at a point of reception. Sound contour plots displaying broadband (dBA) sound levels presented as color- coded isopleths are provided in Figure 4.13-2. The sound contours are graphical representations of the cumulative noise associated with full operation of the equipment and show how operational noise would be distributed over the surrounding area of the Project site. The contour lines shown are analogous to elevation contours on a topographic map, i.e., the noise contours are continuous lines of equal noise level around some source(s) of noise. Table 4.13-8 shows the projected exterior sound levels at the property boundary of each NSA. The results indicate that the Project will not comply with applicable regulations at seven non-participating NSAs using the modeled equipment's noise levels. In order for the Project to reach compliance, mitigation was designed in the form of sound walls with at least 3 pounds per square foot with minimal cracks or gaps. For this specific application, wall geometry (i.e., height, length, and location) is more important than the acoustic mitigation properties of the wall material, provided the wall material is of sufficient mass. Most of the noise received by the neighboring properties would be noise traveling over and around the walls, not through them. The sound wall configuration runs along the perimeter of the Project and between select BESS units. The sound walls' geometric properties are provided below: oo 20-foot-tall section totaling 1,998 linear feet; oo 26-foot-tall section totaling 1,995 linear feet; o0 26-foot-tall section totaling 302 linear feet; o0 26-foot-tall section totaling 308 linear feet; and o0 26-foot-tall section totaling 650 linear feet. Table 4.13-8 and Figure 4.13-3 show the projected exterior sound levels at the property boundary of each NSA with mitigation. The results indicate that the Project will comply with applicable regulations at all non-participating receptors with the implementation of the sound barriers. The noise levels presented in Table 4.13-8 are consistent with the ambient levels shown in Section 4.13.1.4. The highest noise level associated with the mitigated Project operations is 45 dBA at Griffith Energy Storage Project 4.13-13 Tetra Tech/2022120675 Draft Environmental Impact Report August 2023