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City of Santa Ana — Cabrillo Town Center Project <br />August 17, 2023 <br />Page 7of8 <br />• Restrict any activities that result in noise levels in excess of the <br />Thresholds of Significance to the hours of 8:00 AM to 5:00 PM to <br />minimize disruption of sensitive uses. <br />• Implement noise barriers or noise blankets around construction <br />equipment to achieve a minimum noise level reduction of 15 dBA. <br />• Use electric air compressors and similar power tools rather than diesel <br />equipment. <br />i. The Metro EIR's Operation Noise Analysis Underestimates the Projects <br />Impacts <br />Finally, the Metro EIR's operation noise analysis and mitigation measures must be <br />revised. The Metro EIR includes an analysis of HVAC noise associated with new <br />developments in the overlay zon,. The calculation starts with the assumption that <br />HVAC systems "can result in noise levels that average between 50 and 65 dBA, Leq at <br />50-feet from the equipment", then reasons that shielding around rooftop equipment <br />might typically be expected to provide 15 dBA of noise reduction, resulting in a net <br />noise level at 50-feet of 50 dBA. Metro EIR at 4.9-19. For equipment that runs 24- <br />hours per day, the preparers point out that the relationship between the Leq noise level <br />and the CNEL is 6.7 dBA, so that an Leq of 50 dBA at 50-feet would equate to a <br />CNEL of 57. And since 57 CNEL falls below the proposed 65 CNEL significance <br />threshold, the Metro EIR concludes that HVAC noise is less than significant. As <br />noted by noise expert Steve Rogers, such analysis is problematic for at least two <br />reasons. <br />Firstly, the estimate of HVAC unit noise seems too low for a mixed -use project <br />that will likely have hundreds of HVAC units operating simultaneously. This is <br />because the combined effect of multiple similar noise sources grouped together <br />is calculated from the equation: Total Noise Level = Noise Level for Single <br />Source x 10*LOG10 (Number of Sources) So, while we would expect that a <br />single AC unit, serving a single apartment could produce a noise level of <br />approximately 55 dBA at 50-feet, a grouping of 100 units (for example serving <br />one section of the building) would have a total noise level of 55 + 10*LOGio <br />(100) = 75 dBA at 50- feet. Larger, commercial -grade equipment associated <br />with the commercial and office portions of the project as well as ventilation <br />fans for the parking structure (if required) would likely produce more noise <br />City Council 18 — 296 10/3/2023 <br />