Item 18 - Appeal Application Nos. 2023-02 and 2023-03 for Cabrillo Town Center project

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where the existing noise levels exceed the 60 dBA CNEL standard established in the General Plan. Mitigation Measure MM-OZ 4.9-5 would ensure that exterior living spaces, such as porches and patios are constructed in a manner that noise levels do not exceed the 65 dBA CNEL. Further implementation of Mitigation Measure MM-OZ 4.9-6 would ensure that interior living spaces of the residential units do not exceed 45 dBA CNEL. Therefore, this impact would be reduced to a level of less than significant. Heating, ventilation, and air conditioning (HVAC) systems that would be installed for the new residential building associated with the Overlay Zone can result in noise levels that average between 50 and 65 dBA Leq at 50 feet from the equipment. As 24-hour CNEL noise levels are about 6.7 dBA greater than 24-hour Leq measurements, this means that the HVAC equipment associated with the retail -commercial buildings could generate community noise levels that average between 57 to 72 dBA CNEL at 50 feet when the equipment is operating constantly over 24 hours. These HVAC units would be mounted on the rooftops of the proposed buildings and would be screened from view by building features. However, the installation of shielding around these HVAC systems would be required as part of the Overlay Zone, as stated in Mitigation Measure MM-OZ 4.9-7 below. The shielding installed around these systems would typically reduce noise levels by approximately 15 dBA, which could reduce HVAC system noise to approximately 50 dBA Leq at 50 feet from the equipment, which would be approximately 56.7 dBA CNEL. Implementation of Mitigation Measure MM-OZ 4.9-1 would ensure that impacts related to the HVAC systems would remain below the 65 dBA CNEL "Desirable Maximum" exterior noise level guideline established in the City's General Plan for high density residential uses. As such impacts to residents of the Overlay Zone relating to HVAC systems were determined to be less than significant. Operation of the Overlay Zone would not include special events or temporary activities which would cause an increase in ambient noise levels. In addition, operation of the Overlay Zone would not require periodic use of special stationary equipment that would expose off -site sensitive receptors to an increase in ambient noise levels above those existing without the Overlay Zone. Therefore, there would be no temporary or periodic noise impacts to on- or off -site receptors due to operation of the Overlay Zone. This impact was determined to be less than significant. Groundborne Vibration The Certified EIR stated that construction -related vibration has two potential impacts. First, vibration at high enough levels can result in human annoyance. Second, groundborne vibration can potentially damage the foundations and exteriors of historic structures. Groundborne vibration that can cause this kind of damage is typically limited to impact equipment, especially pile drivers. Construction activities that would occur under the Overlay Zone have the potential to generate low levels of groundborne vibration. Vibration that would be experienced from the use of construction equipment ranges from a small bulldozer, which reaches as high as 58 vibration decibels (VdB) at a distance of 25 fee, and an impact pile -drivers, which reaches as high as 112 Cabrillo Town Center City of Santa Ana Technical Memorandum August 2023 City Council 18 — 599 10/3/2023