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Administrative Draft Environmental Impact Report Gill Medical Center Project 4.15.4 Environmental Impacts and Mitigation Measures 4.15.4.1 Thresholds of Significance According to Appendix G of the CEQA Guidelines, noise impacts are considered significant if implementation of the proposed project would result in: Generation of a substantial temporary or permanent increase in ambient noise levels in the vicinity of the project in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies. Generation of excessive groundborne vibration or groundborne noise levels. For a project located within the vicinity of a private airstrip or an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, would the project expose people residing or working in the project area to excessive noise levels. For purposes of this analysis, Project construction noise is compared to the NIOSH standard of 85 dBA for more than 8 hours per day, since construction work is anticipated to span a typical workday of 8 hours daily. The increase in transportation-related noise is compared against the County or City noise standard, where appropriate. In the case that the existing transportation-related noise already exceeds the appropriate standard under current conditions, Project noise contribution is compared to the FICON recommendation for evaluating the impact of increased traffic noise. Noise generated onsite is compared against the County's non-transportation/stationary noise standards identified in Table 4.15-5 and 4.15-8 above. 4.15.4.2 Methods of Analysis This analysis of the existing and future noise environments is based on noise prediction modeling and empirical observations. Predicted construction noise levels were calculated utilizing the FHWA's Roadway Construction Model (2006).Transportation-source noise levels in the Project vicinity were calculated using the FHWA Highway Noise Prediction Model (FHWA-RD-77-108). Onsite stationary source noise levels have been calculated with the SounclPLAN 3D noise model, which predicts noise propagation from a noise source based on the location, noise level, and frequency spectra of the noise sources as well as the geometry and reflective properties of the local terrain, buildings and barriers. In the analysis below the size, location and noise producing level of each source is discussed in detail. Groundborne vibration levels associated with construction-related activities for the Project were evaluated utilizing typical groundborne vibration levels associated with construction equipment. Potential groundborne vibration impacts related to structural damage and human annoyance were evaluated, taking into account the distance from construction activities to nearby structures and typically applied criteria for structural damage and human annoyance. Noise 4.15-18 October 2021