X. NOISE

1. The substation site is located adjacent to Interstate 880 and on the 65 dBA, L_dn noise contour designated for operations of the San Jose International Airport (SJIA). Construction noise levels at and near locations on the project site would fluctuate depending on the particular type, number, and duration of use of various pieces of construction equipment. The effect of construction noise would depend upon how much noise would be generated by construction, the distance between construction activities and the nearest noise-sensitive uses, and the existing noise levels at those uses. Construction noise would be intermittent, extended over a period of four months at the substation site. Construction of pole foundations, erection of poles, and stringing of lines would also generate noise near residences along the proposed power line alignments.

   The noisiest phases of construction would generate approximately 89 Leq at 50 feet (U.S. EPA, 1971). The receptors nearest proposed construction activity would be three existing single-family residences and one multi-family residence on Stockton Avenue, approximately 100 feet from the eastern project site boundary. Consequently, construction noise during construction would generate noise levels up to approximately 83 Leq at the nearest residences during regrading and resurfacing activities.

   Given ambient noise levels at these residences, construction noise would be noticeable; however, many residences are less occupied during the daytime. Construction noise would be annoying to residents at home during the daytime, but it would be a short-term effect. During nighttime, temporary construction-related noise could be more noticeable (since background noise is lower) and could annoy the closest residents given the more sensitive nature of the nighttime period. Therefore, without appropriate limitations on allowable hours of construction, this temporary impact could be significant.

   Transformers on the substation site would generate operational noise. The potential for noise impacts from the transformers is addressed in a Noise Impact Assessment study prepared for the proposed project (Geier & Geier, 1997). This study found that the three transformers proposed for the site would each generate a noise level of 74 dBA, and a composite noise level of 77 dBA at a distance of ten feet. The report predicts a resultant noise level of 52 dBA at the nearest residences (fronting on Stockton Avenue). This projected noise level at the nearest residences due to the transformers is below the ambient noise level during daytime and evening hours, but substantial enough to be faintly audible during 10 percent of the quieter nighttime hours, which were monitored to be 48 to 51 dBA.

   The project design includes construction of an eight-foot high sound barrier. The sound barrier is sufficient to block the line-of-sight between the transformers and single-story residential land uses to the east, and would provide additional noise reduction of approximately 5 to 7 dBA. With appropriate construction of the proposed sound barrier, operating noise from the proposed transformer would be 45 to 47 dBA at the closest residences, which would be below the existing monitored nighttime noise levels. With construction of the sound barrier, transformer-related operational noise is not expected to significantly affect the existing ambient noise environment. The second story of adjacent two-story residences on Stockton Avenue may not experience a benefit from the proposed sound wall. However, increases in noise levels would not be considered substantial in a noise environment dominated by vehicle traffic on the adjacent I-880 freeway.

   Long-term noise levels resulting from the transformers is predicted to be 64 dBA, CNEL at the nearest residences, which would not exceed the existing long-term noise levels of 65 to 67 dBA, CNEL. This prediction applies a 5-dBA "penalty" to account for human sensitivity to the pure tone component of transformer noise. With appropriate construction of the proposed sound barrier, long-term operating noise from the proposed transformers would be 57 to 59 dBA, CNEL at the closest residences. This would result in a one dBA, CNEL increase in existing noise levels, which would not be considered substantial, or perceptible.

   Under certain conditions (such as wet weather or dirty insulators), power lines can create corona-generated noise, usually associated with a buzzing or crackling. Given the number of rainy days per year within the Santa Clara Valley, and PG&E’s practice of high-pressure washing of insulators, corona-generated noise, while occasionally audible, would not be considered a substantial increase to the typical urban noise environment.

   Mitigation

   The following mitigation measures would reduce the potential impact to a less than significant level:

   Mitigation Measure X.a-1: To reduce the construction noise effects, PG&E shall ensure that noisy construction activities at the substation site and near residences along the power line route shall be limited to the least noise-sensitive times of day and week (e.g., 7:00 a.m. to 6:00 p.m., Monday through Friday).

   Mitigation Measure X.a-2: To reduce the construction noise effects, PG&E shall ensure that all construction equipment used on the substation site and for power line construction shall be adequately muffled and maintained.

   Mitigation Measure X.a-3: To reduce the construction noise effects, PG&E shall ensure that all stationary construction equipment (i.e., compressors and generators) shall be located as far as practicable from the eastern property line.

   PG&E shall certify compliance with these measures in scheduled progress reports to the CPUC.

2. As discussed in the response to Item X.a., the noise levels resulting from project operation would be less than ambient noise levels and would be considered a less than significant impact.

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