P & D CONSULTANTS - 2002 - Laserfiche WebLink

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Grand Avenue Widening Project Environmental Impact Report Section 3.0 measurement locations were selected to represent the noise environment throughout the project area, and in areas where project related traffic changes might affect noise sensitive land uses. The noise monitors used for the measurement survey were Brael & Kjwr Type 2236 sound level meters. These analyzers meet the American National Standards Institute (ANSI) S 1.4 specification for a precision sound level meter. Briiel & Kjmr type 4188 %z -inch air condenser microphones were used. The measurement systems were calibrated before and after each measurement with a Briiel & Kjaer Type 4231 sound level calibrator with calibration traceable to the National Institute of Standards and Technology. The results of the noise measurement survey are shown in Table 3.6-3. The quantities measured were the Equivalent Noise Level (Leq), the maximum noise level (Lmax), the minimum noise level (Lorin) and the Percent Noise Levels (L%). Percent Noise Levels are one method of characterizing the dynamics of ambient noise. For example, L90 is the noise level exceeded 90 percent of the time and represents the background or quieter noise level, L50 is the level' exceeded 50 percent of the time and represents the average noise level, and L10 is the level exceeded 10 percent of the time and represents the peak or intrusive noise levels. The results of the survey, which represent existing noise levels from traffic on Grand Avenue, are described in the following paragraphs. The existing noise measurements and modeling were based on 1999 traffic volumes. The existing traffic volumes in 2002 are not expected to be substantially different than in 1999 because there have not been substantial changes in land use or the circulation system in the Grand Avenue area over this period of time. In addition, in general, for changes in traffic volumes to result in a significant change in noise levels (defined as an increase of 3 dB or more), traffic volumes would have to double over that period. Typically, a city such as the City of Santa Ana will experience an annual growth rate in traffic volumes of only a few percentage points for an area that is substantially built out like the Grand Avenue project area. If the traffic in this area had increased by a total of ten percent over the three year period (1999 to 2002), the increase in noise levels would be less than 0.5 dB, which is not significant. Therefore, the noise environment measured in 1999 is considered to be representative of the noise environment in the Grand Avenue study area in 2002. Existing Noise Exposure The results in Table 3.6-3 show that the existing noise sensitive uses directly adjacent to Grand Avenue are currently impacted by traffic noise. The residences most heavily affected are those on the east side of Grand Avenue between Seventeenth Street and the I-5 Freeway, and on the west side of Grand. Avenue between Fruit and Fourth Streets. As shown in Table 3.6-3, the residences on the east side of Grand Avenue between Seventeenth Street and the I-5 Freeway are exposed to significant noise levels during peak traffic hours. The rear yards of these residences have some mitigation in the form of existing walls or fences. The residences on Eastwood Avenue are further away from Grand Avenue, resulting in a lower noise exposure level for these residential uses. The residences on Eastwood Avenue and Fourteenth Street are also exposed to noise from traffic on I-5. F: IPROJ-ENMGrand eirlNew Text - GrandlSection 3 SplitlSection 3.6.doc Page 3.6-8