September 26, 2014
The Village continues to be concerned with excessive noise from bridge construction. The sheet pile driving on and near the shoreline was very loud, but the noise graphs on the Thruway website didn’t show levels as high as we thought the pile driving was producing. Back in June we asked the Thruway to show us their compliance plan and incident reports, so we could understand how they are measuring noise and enforcing the limits of the contract. We wanted this to gain confidence that they are effectively enforcing the limits required in the environmental impact study and the construction contract with TZ Constructors. Unfortunately, up until this week, the Thruway had not provided us with the documents.
The Trustees also decided to hire an expert noise consultant, Brook Crossan, to help us. Mr. Crossan was able to obtain a loan of a sophisticated Brüel and Kjær noise monitor, so the Village could conduct our own measurements. This last Tuesday, Mr. Crossan presented his preliminary report to the Board of Trustees.
He told the Board that he was limited in his ability to evaluate the Thruway’s noise monitoring because he did not receive the compliance plans and reports we had requested, nor access to the noise readings from the Thruway’s monitoring equipment. However, by using the information from the Village’s equipment, he was able to make some determinations.
Mr. Crossan explained that there are two main issues. One is how far away the monitor is placed from the noisy activity. The second is how to present the noise measurement.
The contract noise limits are specified, not to be exceeded: a) at the shoreline for work out in the river, and b) 50’ away for work done on land. The monitor at Salisbury is at a fixed location. It is estimated to be about 400’ from where the pile driving was being done on Piermont Ave and it isn’t at the closest shoreline point to the sheet pile driving for the coffer dams in the water next to the trestle.
The Thruway’s website shows noise levels in what is called Leq(15). This means that the noise readings are averaged over a 15 second period. This type of averaging is typically used for monitoring long-term exposure when noise is fairly constant. Mr. Crossan explained that Leq(15) isn’t appropriate for measuring the very short pounding from pile driving. Another type of measurement, Lmax, which shows the maximum noise level is more appropriate. In fact, the construction contract limits are specified as Lmax levels.
The Thruway and TZ Constructors compliance teams have told us they also use hand held meters to enforce the limits, but we have not been given access yet to their readings or reports.
For the first week, Brüel and Kjær’s equipment was placed next to the Thruway’s equipment at Salisbury point. The Leq(15) readings from our equipment matched the Thruway’s. The monitor was then moved as close as we could get to the sheet pile driving, estimated to be about 100’ away. During that period, there were several readings that exceed the 90db Lmax limit. Adjusting for the distance, Mr. Crossan concluded that the noise exceed the 90db limit every day that week.
We have asked the Thruway to reconfigure the website to show Lmax levels and to eliminate the 30 minute delay before the readings are displayed. The Thruway has said that the noise levels are “now within allowable levels” and stated that they would work on giving us the documents we requested.