P & D CONSULTANTS - 2002 - Laserfiche WebLink

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Grand Avenue Widening Project Environmental Impact Report Section 3.0 Between Seventeenth Street and Santa Ana Boulevard, the second row of dwellings is between 92 and 129 feet from the centerline of Grand Avenue. At these distances, the projected noise exposure level at these residences for the 2020 with project case will range from 66.3 dB CNEL to 64.1 dB CNEL. The second row of residences between Santa Ana Boulevard and Fourth Street is 167 feet from the centerline of Grand Avenue. When the first row of residences is removed, the second row of dwellings will be exposed to a noise level of 63.2 dB CNEL. The second row of residences between Fourth and First Streets are between 120 and 169 feet from the centerline of Grand Avenue. The projected noise level at these lots for the 2020 with project case will range from 65.2 dB CNEL to 63.0 dB CNEL. The exterior noise standard for the City of Santa Ana is 65 dB CNEL. Therefore, all noise sensitive land uses subject to traffic noise levels in excess of 65 dB CNEL as a result of the widening of Grand Avenue under either Alternative 1 or 2 will require noise barriers. This includes the second row of residential dwellings located within the 65 dB CNEL noise contour for the 2020 with project case. The distances to the 65 dB CNEL noise contour for the 2020 with project case are listed in Table 3.6-9. TABLE 3.6-9 DISTANCES TO 65 DB CNEL NOISE CONTOUR FOR THE 2020 WITH PROJECT CASE Grand Avenue Distance from Centerline ft. Seventeenth Street to Santa Ana Boulevard 112 Santa Ana Boulevard to Fourth Street 127 Fourth Street to First Street 124 Mitigation through the design and construction of a noise barrier (wall, berm or combination wall/berm) is the most efficient method of reducing traffic noise levels. The effect of a noise barrier is critically dependent on the geometry between the noise source and the receiver. A noise barrier effect occurs when the barrier breaks the "line of sight' between the noise source and the noise sensitive receiver. The greater the distance the sound must travel around the barrier to reach the receiver, the greater the noise reduction of the barrier. A barrier which does not break the line -of -sight is not an effective barrier, while one which just interrupts the line -of - sight achieves a five dBA reduction in noise. The FHWA model was also used in a computerized format to determine barrier heights in this analysis. Noise barrier calculations were performed for each of the noise sensitive properties which will be exposed to an increase in noise due to the removal of an adjacent property under Alternatives 1 and 2. Noise barriers are required for all noise sensitive land uses exposed to noise levels exceeding 65 dB CNEL. The residential lots requiring noise barriers are listed in bold in Tables 3.6-10 and 3.6-11. The results of the calculations show that a noise barrier, 5.5 feet in height relative to the residential pad elevation, will be sufficient to reduce the projected noise levels at each of the exposed noise sensitive land uses for the 2020 with project case, to below the City of Santa Ana exterior noise standard. This noise barrier height will be sufficient for all exterior F.•IPROJ-ENVIGrand eirWew Text - GrandlSection 3 SplitlSection 3.6.doc Page 3.6-39