Underwater and airborne acoustic measurements were recorded as part of the Explosive Handling Wharf-2 (EHW-2) project located at Naval Base Kitsap at Bangor, Washington. Acoustic data was collected during vibratory and impact pile driving activities between September 28, 2012 and January 19, 2013. The September 28th date coincides with the beginning of the in-water work for the EHW-2 project. Regulatory permits and consultations completed for this project identified several terms, conditions, and metrics which the Navy was required to comply with. The acoustic monitoring was conducted to support the respective Biological Assessment (BA) and Incidental Harassment. Authorization (IHA) compliance documents for this project, NAVFAC 2011a and 2011b, both provide a more in-depth discussion on the modeling assumptions and calculations for the project and are incorporated here by reference.
The objective of the monitoring for the EHW-2 project was to supplement the findings from the Test Pile Program (TPP) project, verify the propagation rates of underwater and airborne sounds and compare the performance of the bubble curtain to other projects. Predictions of the distances to applicable criteria were estimated for the EHW-2 project for fish, birds and marine mammals.
Statistically significant comparisons between the EHW-2 project and the TPP project could only be made for the 36-inch pile data. With the TPP project there was only one 24-inch pile driven and during the EHW-2 project there was only one 48-inch pile driven. As a result, The comparisons were made for the 36-inch piles for both projects and between the 24-inch and 36- inch piles for the EHW-2 only are summarized in Table ES1. For the impact pile driving in Table ES1, all data are with a bubble curtain.
Typically a bubble curtain will provide approximately 10 dB of attenuation in the peak sound pressure levels when properly designed and deployed. At times it appeared the bubble curtain achieved close to 10 dB of attenuation and other times it clearly did not. There was no provision available to determine for the purposes of this report if there was the proper air flow or if the bubble curtain fully encapsulated the pile. EHW 2 contractors are in the process of redesigning the bubble rings to improve their performance.
The calculated maximum distance for the 206 dB peak zone is calculated using the 208 dB and the 15.8 dB propagation rate shown in table ES-1. The average calculated RMS levels for the 36 inch TTP pile are from page 106 in the TTP report. The Average 187 and 183 dB cumulative SEL is calculated using 100 pile strikes and the propagation rate and average single strike SEL from Table ES-1.