Item 28 - Public Hearing - ZOA No. 20204-01 South Coast Technology Center

Home Browse Search

South Coast Technology Center Project CEQA Exemption 15183 a given time, they are expressed as Leq noise levels. Therefore, the noise level threshold of 80 dBA Leq over a period of eight hours or more is used to evaluate the potential project -related construction noise level impacts at the nearby sensitive receptor locations. Noise levels from construction equipment and activities were modeled using the Federal Highway Administration's Roadway Construction Noise Model (RCNM). Related to operational noise from a stationary source for the City of Santa Ana, a project would result in a significant impact if project -related operational noise levels exceed the daytime exterior 55 dBA Leq and nighttime exterior 50 dBA Leq noise level standard at nearby sensitive receiver locations (based on the exterior noise level standards in SAMC Section 18.312). The nearest residential uses to the Project Site are located within the City of Costa Mesa. The City of Costa Mesa's residential exterior noise standards are effectively the same as the exterior noise level standards in SAMC Section 18.312,31 which would be applied when analyzing noise impacts for residential uses. A project would result in a significant impact if project -related operational (stationary -source) noise levels exceed the daytime exterior 55 dBA Leq and nighttime exterior 50 dBA Leq noise level standard at the nearest residential uses. Construction and Operational Vibration Standards The FTA Transit Noise and Vibration Impact Assessment Manual provides criteria for acceptable levels of groundborne vibration for various types of buildings, which are shown in Table 4.13-2, Structural Vibration Damage Criteria. As the nearest sensitive receptor structures to Project Site are institutional uses, the architectural damage criterion for continuous vibrations of 0.3 inch -per - second PPV for engineered concrete and masonry is applied for this Project. Table 4.13-2 Structural Vibration Damage Criteria Building Category Peak Particle Velocity for Continuous Sources (PPV) inches/second in/sec] I. Reinforced concrete, steel, or timber noplaster) 0.5 II. Engineering concrete and mason noplaster) 0.3 III. Nonen ineered timber and masonry buildings 0.2 IV. Buildings extremely susceptible to vibration damage 0.12 Source: FTA, Transit Noise and Vibration Impact Assessment Manual, 2018. Human annoyance occurs when construction vibration rises significantly above the threshold of human perception for extended periods of time. The vibration level at which human annoyance is perceived is 0.2 inch per second peak particle velocity (PPV).31 Mobile Noise Threshold An off -site traffic noise impact typically occurs when there is a discernable increase in traffic and the resulting noise level exceeds an established noise standard. In community noise considerations, changes in noise levels greater than 3 dB are often identified as discernible, while changes less than 1 dB would not be discernible to local residents. A 5-dB change is generally 30 The residential exterior noise standards in SAMC Section 18.312 are 55 dBA for daytime (7 am —10 pm) and 50 dBA for nighttime (10 am — 7 pm). The residential exterior noise standards in Costa Mesa Municipal Code Chapter 8 are also 55 dBA for daytime (7 am — 11 pm) and 50 dBA for nighttime (11 am — 7 pm). 31 California Department of Transportation, Transportation Related Earthborne Vibrations, 2002. July 2024 Page 79