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5.0 Environmental Analysis 5.6 Noise <br />Avion Project SEIR <br />Page 5.6-5 <br />Additionally, the project would have a significant groundborne vibration impact if it would result in: <br />• Exposure of the nearest sensitive receiver to hydraulic breakers, hammers, and other non- <br />transient source vibration levels that exceed 0.2 in/sec PPV; or blasting vibration levels that <br />exceed 2.0 in/sec PPV. <br />5.6.4.2 Impacts <br />a. Residential Receivers <br />Construction activities produce varying degrees of ground vibration, depending on the equipment <br />and methods employed. However, with a few exceptions, ground vibrations from typical <br />construction activities very rarely reach levels high enough to cause damage to structures. Noise and <br />vibration generated by general construction activities associated with the project were assessed in <br />the Subarea Plan EIR. Consequently, excavation and other general construction activities are not <br />assessed in this analysis. The noise and vibration analysis focused on the recently identified options <br />for rock removal, including hammering, drilling, and blasting. As with noise, vibrations are <br />attenuated by distance. The vibrations that would be produced by hammering, drilling, a nd blasting <br />would travel relatively short distances as compared to noise. Therefore, the noise analysis focused <br />on the receivers located northeast of the project site (Figure 5.6-1). The nearest receivers are the <br />single-family homes associated with the Heritage Bluffs project, which is currently under <br />construction and will be occupied once construction on this project begins. The nearest receptor is <br />(would be) located approximately 175 feet northeast of the nearest hammering, drilling, and blasting <br />location. The methodology use in the noise analysis is presented in Appendix E. <br />Hammering <br />Noise <br />Mounted hydraulic impact hammers would be used to remove the top of the rock formation. <br />Hydraulic hammers used for rock breaking are assumed to operate at maximum power for <br />approximately 20 percent of a given hour ( FHWA 2008). A loader/backhoe would likely be used to <br />clear broken rock and would have a utilization factor of approximately 40 percent. Rock breaking <br />with hydraulic hammers is calculated to generate maximum noise levels on the order of 90 dB(A) at <br />50 feet. Assuming two hydraulic hammers and one loader/backhoe are operating for a full hour, <br />hydraulic-hammer rock breaking would generate hourly noise levels of 86 dB(A) Leq at 50 feet. Based <br />on standard point source propagation noise levels, noise levels would attenuate to 75 dB(A) Leq at <br />the nearest residential property line 175 feet to the northeast, which would comply with the City’s <br />applicable construction noise level standards. <br />Vibration <br />According to the FTA, vibration levels associated with the use of mounted impact hammers are <br />0.089 in/sec PPV at 25 feet. Using FTA’s recommended procedure for applying a propagation <br />adjustment to these reference levels, vibration levels would exceed Caltrans-recommended <br />threshold (0.2 in/sec PPV) at distances of 14 feet or less from a mounted hydraulic hammer. <br />Vibrations at various distances are shown in Table 5.6-1. Vibration levels are anticipated to attenuate