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<br />6.2A <br />Page 42 <br /> <br />Noise impacts associated with tunnel construction would primarily occur at tunnel entry and exit <br />shafts, where construction staging would occur. Since tunnel construction would proceed 24- <br />hours per day (three eight-hour shifts or two 10-hour shifts and a four-hour shift, or some other <br />combination) on weekdays, some nighttime activity in support of tunnel construction would <br />occur at the shafts, in addition to the more intensive daytime activities. Most of the activity <br />would occur at the entrance shaft, which would be located at the Ravenswood Valve Lot. <br /> <br />Construction-related activities would occur at the entry shaft for approximately four years, with <br />tunnel construction over two to three and a half of those years. Draft EIR Table 4.12-13 shows <br />that daytime construction noise levels would not exceed the 70 dBA speech interference criterion <br />at the closest residential receptors and, therefore, would be less than significant. However, as <br />indicated in Draft EIR Table 4.12-16, nighttime operation of the cranes, ventilation fan, front- <br />end loader, segment truck in the shaft vicinity and of the water treatment facilities in the pipeline <br />tie-in vicinity would expose the closest residential receptors to the south (on Fordham Street) to <br />noise levels that exceed the 50 dBA sleep interference criterion by up to 20 dBA. Noise from <br />backup alarms also could be a significant impact because of the long construction duration and <br />use of these alanns during nighttime activities. Therefore, because much of this equipment <br />would need to be operated at night -- ventilation fans are required at all times that workers are <br />underground, which would be up to 24-hours a day, cranes would be operated at night to raise <br />and lower workers as necessary, and pumps would be operated as often as necessary (up to 24- <br />hours per day) to maintain dry working conditions underground - temporary noise impacts from <br />nighttime activities associated construction at the Ravenswood Valve Lot would be significant <br />and unavoidable. <br /> <br />. Mitigation Measure NOI-la: Noise Control Measures <br /> <br />Impact NOI-ld would be partially mitigated through the actions described in Mitigation Measure <br />NOI-la, as well as Mitigation Measure NOI-l b, which requires preparation of a noise control <br />pan by the construction contractor. However, residential receptors with direct line of sight to the <br />shaft construction and associated nighttime construction activities could still be occasionally <br />exposed to an exceedance of the 50 dBA sleep interference criterion. <br /> <br />Impact NOI-le: Nighttime construction at the Newark tunnel shaft would result in a <br />substantial temporary increase in existing ambient noise levels in the Project vicinity, <br />affecting people and captive wildlife. <br /> <br />Construction activities at the Newark tunnel shaft site would occur off and on over the four-year <br />tunnel construction duration, extending as long as two and a half of those years. Nighttime tunnel <br />construction activities at the Newark shaft (operation of the cranes, ventilation fan, front-end <br />loader, and stationary equipment such as generators, air compressor, pumps associated with <br />water treatment and dewatering, etc.) could exceed the 50 dBA sleep interference criterion at the <br />closest residential receptors with direct line-of-sight (2,000 feet to the east) by as much as 4 <br />.. dBA, which would be a si~tlificant noisei~p.~~t.~..... <br /> <br />The Ohlone Humane Society Wildlife Rehabilitation Center is located approximately 230 feet <br />north of the proposed tunnel shaft site. The center currently locates noise-sensitive animals in <br />enclosures facing to the north and as far north as possible, away from railroad tracks, which are <br />located immediately south of the Center. These tracks are located between the Center and <br />proposed shaft site. Daytime and nighttime tunnel-related construction activities would generate <br />noise levels at the Center's closest enclosures that exceed the 60 dBA significance criterion by as <br />much as 18 dBA during the day and 13 dBA during the night. The Center's current practice to <br />locate noise-sensitive aninlals in enclosures that face away and as far north as possible (away <br />from the shaft site) would help reduce potential noise disturbance. <br /> <br />32 <br />