EXHIBIT 4-2_55A_BRISTOL WIDENING TECHNICAL STUDIES

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4.2 Acoustic Impact Analysis Short -Term Acoustic Impacts IL Short -term acoustic impacts are those associated with construc- tion activities necessary to implement the Bristol Street Widen- ing Project. These noise Levels will be higher than the ambient noise levels in the project area today but will subside once construction is complete. Construction is expected to begin in the year 1989, with construction activities occurring over a period of 6 months. Two types of noise impact should be considered during the con- struction phase. First, the transport of workers and equipment to the construction site will incrementally increase noise levels along the roadways leading to and from each specific construction site. The increase should not exceed 1.0 dB(A), when averaged over a 24 -hour period, and should therefore be an inaudible increase to noise receptors located along the roadways utilized for this purpose. Second, the noise generated by the actual construction activities at each construction site should be evaluated. Construction activities are carried out in discrete steps, each of which has its own mix of equipment, and Consequently its own noise charac- teristics. These various sequential phases will change the char - acter of the noise levels surrounding the construction site as work progresses. Despite the variety in type and size of con- struction equipment, similarities in the dominant noise sources ! and patterns of operation allow noise ranges to be categorized by 1] work phase. Figure 12 illustrates typical construction equipment noise ranges at a distance of 50 feet. The earth moving equipment category includes excavating machinery I (backhoes, bulldozers, shovels, trenchers, front loaders, etc.) and highway building equipment (compactors, scrapers, graders, pavers, etc.). Typical operating cycles may involve one or two minutes of full power operation followed by three to four minutes at lower power settings. Noise levels at 50 feet from earthmov -- ing equipment range from 73 to 96 dB(A). The Environmental Protection Agency has found that the noisiest equipment types operating at construction sites typically range from 88 to 91 dB(A) at 50 feet. Although noise ranges were found to be similar for all construction phases, the erection phase (laying sub -base and paving) tended to be less noisy. Noise levels varied from 79 dB(A) to 89 dB(A) (energy average) at 50 feet during the erection phase of construction. City Standards: The construction noise impact to the adjacent noise sensitive land uses will be a temporary nuisance. The City of Santa Ana Noise Ordinance from the Municipal Code requires that construction activities take place only during weekday day- 4-13