Section 1 Introduction - National Marine Fisheries Service - NOAA

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NBK at Bangor EHW-1 Pile Replacement Project Final <strong>Marine</strong> Mammal Monitoring Report Airborne Behavioral Harassment Zones: a. 100 dB for all pinnipeds except harbor seals b. 90 dB for harbor seals. Two hydrophones were typically used to take underwater measurements at four measurement locations to accurately capture sound propagation characteristics both within and outside of the WRA. An air bubble curtain system was not used during pile driving at EHW-1 because all pile driving utilized a vibratory pile driver, and sound attenuation devices were not required for vibratory driving for this project. Ambient underwater and airborne conditions in the absence of construction activities were recorded for comparison. The U.S. Navy’s Acoustic Monitoring Plan (Appendix A) provides the specific details of the acoustic monitoring requirements and protocol for both underwater and airborne sounds from the EHW-1 PRP. Underwater sound measurements were conducted at positions both near pile driving and at distant locations. Underwater sound measurements were recorded at 10 meters from the pile to obtain reference readings during vibratory pile driving. These recordings were conducted under a contract with Manson Construction, by Robert Miner Dynamic Testing, Inc. (RMDT). All results associated with these measurements are documented in a separate report (RMDT 2012) which is an appendix to the EHW-1 Acoustic Monitoring Report (NAVFAC 2012). The position of the hydrophones was maintained using a line extending upward from a small steel anchor, with the hydrophones and associated signal cable raised or lowered on that anchor line. The steel anchor and anchor line were typically deployed from the existing wharf so as to make possible an unobstructed “line of sight” between the pile and each hydrophone. Far-field acoustic measurements were conducted under a contract with HDR, Inc. by the acoustic firm Illingworth & Rodkin. Measurements were conducted from three primary locations – a vessel within the WRA, a vessel stationed near mid-channel, and an autonomous raft near Toandos Peninsula – to determine the extent of marine mammal threshold isopleths. Sound measurements at these locations were typically taken at two depths: one at 10 m, and the other at 20 to 30 m, or 2 to 3 m above the bottom, depending on the depth of the water column. Hydrophones were attached to a weighted line that was deployed from the surface. Tension on the hydrophone signal lines was minimized to reduce strumming noise. However, it was not possible to eliminate all strumming effects during conditions with strong wind, waves, and strong currents. Measurements were conducted inside the WRA at varying distances that typically ranged from 100 to 170 m, although measurements ranged anywhere from 55 to 1,450 m. Measurements were also conducted outside the WRA at distances that were typically beyond 700 m. The hydrophones on the WRA boat measured sound levels in 1-second intervals throughout each workday. While most of the underwater hydrophones and microphones recorded data continuously and were downloaded periodically to obtain the raw data,, some of the acoustic recording equipment provided visual readings in “real-time” on the sound level meters (SLMs). All the data was analyzed after the completion of the project. Stationary Hydrophones. A stationary 2-channel hydrophone recording system was suspended from the wharf to record sounds at approximately 33 ft (10 m) from each pile. Hydrophones were deployed taking into account tidal variations and were typically deployed with one at approximately 3 ft (1 m) above the mudline and the other hydrophone at a depth equal to one half the water depth, or typically 30 to 40 ft. The equipment field configuration of the Bangor, Washington 20
NBK at Bangor EHW-1 Pile Replacement Project Final <strong>Marine</strong> Mammal Monitoring Report hydrophones allowed for direct field verification of proper function and calibration by means of a calibrated piston-phone sound source. Each measurement day the configuration and instrument settings were checked using a Gras Model 42AC piston-phone with a hydrophone adaptor. The piston-phone was field checked, in turn, using a Class 1 Sound Level Meter (SLM) with a ½" microphone. In addition to the hydrophone array near the piles, a two channel stationary hydrophone array was deployed near the Toandos Peninsula from an anchored inflatable raft (RFT). The RFT position was an unattended system deployed in waters approximately 18 to 20 meters in depth. One hydrophone was suspended at approximately mid-depth at mean water depth and the other at a position approximately 2 ft (0.61 m) above the bottom at low tide. The distance between the EHW-1 and the RFT position ranged from about 7,710 – 7,875 ft (2,350 to 2,400 m) throughout the project. The SLMs associated with the hydrophones collected data every day and night for several consecutive days at a time. All data was analyzed after the completion of the project. Vessel-Based Hydrophones and Microphones. All SLMs were calibrated to the hydrophone response with the pistone phone signal and hydrophone coupler at the beginning of each day. The response of SLMs to the calibration tone was noted in field logbooks and logged by the SLM, which was downloaded after each day with a pile driving event. SLMs were used for realtime data acquisition and post-testing recording analysis. One acoustic vessel within the WRA was equipped with a two-channel hydrophone array which was used inside the WRA to monitor near-filed isopleths for marine mammals . The SLM associated with these hydrophones recorded continuously during pile driving and collected data in real time. In addition to the WRA vessel, a mid-channel vessel (MID) was also used as a platform for deployed hydrophones. The systems outside of the WRA were used to estimate the distances to the marine mammal behavioral threshold isopleths. The MID drifted or was anchored in the channel of the Hood Canal. For the majority of the EHW-1 PRP, the MID remained in the vicinity of the WRA fence (i.e., beyond ± 800 m from the pile driving). But there were times when it was positioned as close as 715 m and as far as 10,000 m from EHW-1. The SLM associated with these hydrophones recorded continuously during pile driving. For each pile being driven, an airborne microphone was located on the WRA vessel at approximately 55 to 1,450 m from the pile to record airborne sound levels. The microphone was positioned at 4.5 m above the seafloor. Stationary Microphones. Two land-based microphones were placed to the north and south of the EHW-1 project site. The south stationary airborne system was removed on 7 October 2011. All airborne data were recorded and analyzed after completion of the project. Bangor, Washington 21
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Section 1 Introduction - National Marine Fisheries Service - NOAA

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