5A Public Hearings 2018 0507 - Laserfiche WebLink

Home

Environmental Checklist Noise Initial Study – Mitigated Negative Declaration 69 percent, it would not increase traffic noise by more than 0.4 dBA Leq (roughly equivalent to 0.4 dBA Ldn in an urban setting). Therefore, project-generated traffic on nearby roadways would incrementally increase ambient noise levels but below significant levels. The project would not result in exposure of persons to or generation of noise levels in excess of standards and would not result in a substantial permanent increase in ambient noise levels. Impacts would be less than significant. LESS THAN SIGNIFICANT IMPACT b. Would the project result in exposure of persons to or generation of excessive groundborne vibration or groundborne noise levels? The FTA describes the general human response to different levels of groundborne vibration velocity levels as follows (2006):  75 VdB - Approximate dividing line between barely perceptible and distinctly perceptible  85 VdB - Vibration acceptable only if there are an infrequent number of events per day  90 VdB - Difficulty with tasks such as reading computer screens This analysis uses the FTA’s vibration impact thresholds to determine whether groundborne vibration would be “excessive.” The FTA recommends an 80 VdB threshold for infrequent events at residences and buildings where people normally sleep. In terms of groundborne vibration impacts on structures, the FTA states that groundborne vibration levels in excess of 100 VdB would damage fragile buildings and levels in excess of 95 VdB would damage extremely fragile historic buildings. Table 10 identifies various vibration velocity levels at distances from the source for the types of construction equipment that generally generate high levels of vibration and could be expected to be used for project construction. The primary sources of man-made vibration are blasting, grading, pavement breaking, and demolition. As shown in Table 10, a jackhammer would generate the highest vibration levels. At a distance of 1,300 feet, general construction equipment would generate a vibration level of under 60 VdB, which is less than the 80 VdB threshold for infrequent events at sensitive receptors recommended by FTA. Furthermore, 60 VdB is less than the approximate dividing line between barely perceptible and distinctly perceptible (75 VdB). Therefore, vibration impacts associated with construction would be less than significant. Table 10 Construction Equipment and Associated Vibration Levels Equipment Approximate VdB 50 feet 1,300 feet 1,500 feet Jackhammer 88 59.7 58.5 Generators 81 52.7 51.5 Dozer 82 53.7 52.5 Source: Federal Railroad Administration 2006 In addition, operational activities associated with office and advanced manufacturing operations would not generate substantial vibration levels. Thus, the project would not expose people to excessive groundborne vibration or groundborne noise levels. This impact would be less than significant. LESS THAN SIGNIFICANT IMPACT 366