Noise Technical Reports
A noise study needs to be prepared for most development projects to determine the noise exposure and any necessary noise mitigation measures for construction and/or operation. The study needs to be consistent with applicable noise standards of the City or County where the project is located (Municipal Code/Noise Ordinance/Noise Element of the General Plan), and/or significance criteria based on guidance provided by Appendix G of the California Environmental Quality Act (CEQA) Guidelines.
Based on the CEQA guidelines, there are several noise significance criteria, including whether a project would result in:
- Exposure of persons to or generation of noise levels in excess of standards established in the local general plan or noise ordinance or applicable standards of other agencies;
- A substantial temporary, periodic, or permanent increase in ambient noise levels in the project vicinity above levels existing without the project; or
- Exposure of persons to or generation of excessive ground-borne vibration or ground-borne noise levels.
Construction Noise Analysis
For most projects, short-term community noise impact from diesel-powered construction equipment and trucks is the primary concern. Our standard approach to noise analysis is both quantitative and qualitative. This approach includes calculation of logarithmically attenuated construction noise levels at receptor locations for comparison with community noise standards and discussion of the existing noise sources at or near a project site, usually traffic. In some cases, pre-project background noise measurements may be needed, in which case, we will utilize a calibrated one-third octave band integrating sound level meter to measure the ambient noise at the project site and near potential sensitive receptors, such as residences.
For quantitative analysis of construction noise impacts on nearby receptors, we use the U.S. Department of Transportation (DOT) Federal Highway Administration (FHWA) methodology, which utilizes typical noise levels based on actual noise measurements collected during the Boston “Big Dig” project (1991-2006). The FHWA Roadway Construction Noise Model (RCNM) contains reference noise levels for over 50 types of construction equipment in common use, such as bulldozers, excavators, graders, and heavy trucks. Noise impacts are evaluated against community noise standards contained in the noise element of the City or County General Plan for the vicinity of a project site.
Operational Noise Analysis
In some circumstances, long-term operational impacts from increased traffic and mechanical equipment such as heating, ventilation, and air conditioning (HVAC) systems can be an issue if receptors are near or adjacent to a project site. For a large industrial project such as a power plant, the use of large fans in air-cooled condensers can be a significant source of noise. For warehouses, truck loading activities, truck movements, and parking lot vehicle movements may be a concern. We will perform both quantitative and qualitative analysis for operational noise to determine whether the project would be in compliance with the Ordinance and General Plan and if mitigation measures would be needed to reduce the noise to less-than-significant levels. We can use SoundPLAN acoustical modeling software to model project operational worst‐case stationary noise impacts from the proposed project to nearby sensitive receptors.
If the results of the analysis indicate unacceptable noise levels for the nearby properties, we will propose mitigation measures, such as sound-blocking walls or curtains, for installation in the appropriate areas of the project site.
Once the significance of the noise impacts is determined, the analysis methodology and results are documented in a Noise Technical Report, which supports the CEQA document.