May 7, 2013
The Tappan Zee Bridge Task Force and Mayor Christian met today with representatives from the Tappan Zee Bridge project team to discuss construction noise and vibration monitoring.
The project team described their plan to monitor noise, vibration, and air quality during construction; the limits they are not to exceed; and how they will respond if a limit is exceeded. The project website now has a page dedicated to Environmental Monitoring, http://newnybridgegallery.com/noise/. The site describes the monitoring plan and provides real-time display of noise, vibration, and air quality measurements from the monitoring locations.
Construction Hours and Noise Limits
The project contract restricts construction activities late at night (10pm to 6am), Saturday morning until midday and Sunday all day. During that time, no equipment can be used that emits noise above 70 dBA max measured at an offset distance of 50 feet if the work is on land and at the nearest point of the shoreline if the work is in the water.
During non-restricted working hours, noise limits are based on the specific equipment being used. The nosiest activity will be pile driving, with noise levels at 50 feet of upwards of 90dbA. The table of limits is shown on the website. While these limits are allowed by contract until 10pm, TZC says their plans are to start M-F at 6am and end work by 5pm. They say they will work M-F 5pm-10pm and Saturday 12n-10pm only if they get behind schedule.
We reiterated the Village’s previously stated position that noisy construction should be limited to M-F 8am to 7pm with no construction activities on weekends or Federal holidays.
Perceived noise, particularly from pile driving, will be the greatest as the construction gets closer to our shoreline. While it is expected that pile driving farther out in the river will not reach 90db at the shoreline, we expressed concern that repetitive pounding, even at lower decibel levels can be very disturbing. They described that piles will be set mostly be vibrating them into the riverbed. This is much quieter than impact hammering. Once the pile is mostly set using the vibratory hammer, it will be impact hammered at the end to set it into place with a few strikes. They said we should expect that to typically be the nosiest activity and would occur towards the end of the shift.
On the Rockland side, the proposed plan is to place monitoring stations at the shoreline just north and south of the bridge. One at Salisbury Point and one at #28 River Rd. They have asked the Village for permission to place a third monitoring station at Village Hall.
We expressed concerns about the monitoring of construction activities on land between the shoreline and Exit 10. This includes the use of Exit 10 as a staging area and the construction of the shared-use (bike/pedestrian) path and the temporary AETC structures. We believe monitors should be installed to make sure the residential neighborhoods on either side of the Thruway do not experience noise levels above the limits. We asked for their acoustic engineers to look how noise will be received in the hillside neighborhoods overlooking the Thruway.
We also requested the contractor look for ways to minimize the perceived noise from backup alarms on our residents. The trestle (pier) is being made narrower than originally designed, so we asked for them to make sure the revised design still allows for trucks to enter and leave without backing up. The same consideration should be used in the Exit 10 staging area.
The project team described their vibration monitoring plan. They said the expected levels of generated vibrations to be well below the levels that could cause structural damage. However, they have identified properties in close proximity to the construction zone to offer pre-construction surveys and installation of vibration monitoring devices. They are in the process of contacting these property owners for permission. Other concerned property owners may request to be included.