ORPC Maine, LLC submits this Final Report on the Acoustic, Marine Mammal and Bird Monitoring Studies during Phase I Pile Driving Activities for the Cobscook Bay Tidal Energy Project (Project) in compliance with the Incidental Harassment Authorization (IHA) issued by NOAA NMFS, Office of Protected Resources.
Pile driving activities for the installation of ORPC’s TidGen™ bottom support frame were completed between March 24 and April 4, 2012. This work was accomplished in accordance with regulatory restrictions relating to the presence of endangered Atlantic salmon smolt after April 9th (Federal Energy Regulatory Commission, Pilot Project License, P-12711-005, Article 402). Marine mammal monitoring and mitigation requirements for pile driving were conducted in accordance with the IHA issued by NOAA NMFS, Office of Protected Resources, on March 8, 2012.
The contractor utilized several pile driving hammer techniques during the installation. The primary means was a vibratory hammer which produced continuous noise levels. The secondary means was a diesel impact hammer which produced a more acute, instantaneous noise source.
Environmental monitoring was conducted by leading scientists and experts during pile driving activities and included the following:
- In-air acoustic monitoring on Goose Island and at the Lubec On-shore Station • Hydroacoustic monitoring in the near field (from the deployment barge) and at various far field ranges (100 m, 1,000 m, and 2,000 m)
- Marine mammal observations located on vessels anchored around the installation site for all pile driving activity and additionally from land stations for three events
- Marine mammal mitigation measures
- Bird survey from the Lubec shore
Results of monitoring during pile driving activities demonstrated minimal impact to the environment. Source levels measured during impact and vibratory pile driving were below the thresholds of concern for Atlantic salmon smolt. Measured Level A and B isopleths ranges were significantly shorter than the conservative calculated ranges included in the IHA. Although there were sightings of birds and harbor seals in the vicinity of the project area both before and after pile driving, their responses to pile driving noise were minimal. This included harbor seals, or possibly a single individual harbor seal, which returned to the project site (outside the Level A exclusion zone) on multiple days of pile driving.
Mitigation measures used during pile driving were successful in maintaining acoustic source levels within acceptable ranges and minimizing impacts to the environment. These measures included wood sound absorption devices installed in the head of the impact hammer and a “soft start” that initiated pile driving at less than 100% energy for both hammer types. In addition, modifications made by the contractor to the physical connection between the pile and the follower alleviated initial acoustic spikes.
Protected Species Observers (PSOs) were successful in recording marine mammal sightings, determining location and the animal’s behavior. However, marine mammals were not observed within or approaching the Level A exclusion zone (initially estimated to be 500 feet). Shut down or delay procedures, therefore, were not initiated during pile driving activities.
ORPC presented the initial pile driving acoustic results, including the effectiveness of mitigation measures, to NOAA NFMS on April 2, 2012, as part of the agency consultation required for requesting modification of the restrictive window for pile driving. Meanwhile, ORPC submitted a license modification request of Article 402 Restriction Period for Pile Driving to FERC on March 29, 2012, and supplemented this request with additional information on April 2, 2012. FERC approved the modification on April 4, 2012.
ORPC will utilize this same pile driving process in the future if the installation requires it, thereby making the restrictive window unnecessary. This conclusion is supported by Phase I testing results. Moreover, this conclusion supports the virtues of adaptive management which allows scientifically gathered data to guide the evolution of best management practices for environmental monitoring and mitigation measures.
The following best management practices should be incorporated into future pile driving activities in Cobscook Bay to minimize the level of effort while addressing the areas of greatest risk:
- The vibratory hammer in combination with wood sound absorption devices used during Phase I pile driving had source levels below regulatory thresholds.
- Modifications to the physical connection between the pile and the follower alleviated initial acoustic spikes.
- The effectiveness of soft start procedures used during Phase I was difficult to quantify. However, no marine mammals were observed within the Level A exclusion zone or at any time during active pile driving.
- ORPC demonstrated that sound exposure levels (SELs) for vibratory hammer activity are limited by provided best practices are used for hammer and pile assembly.
- Information gathered by experts and submitted by ORPC as a modification request related to the restrictive window for pile driving was used to remove the window for the remainder of Phase I operations. This information remains pertinent to Phase II construction and should be evaluated for this purpose.
- Hydroacoustic monitoring results confirmed that pile driving source levels were within acceptable ranges provided that sound absorption devices were used and best practices were implemented for pile and follower assembly. ORPC will implement these best practices if pile driving is used during Phase II installation, which will occur at the same location/environment and geology as Phase 1. Additional hydroacoustic monitoring, therefore, should not be required.
Marine Mammal Observations
- Measured isopleths ranges for both the impact and vibratory hammer indicate that conducting observations from the installation barge rather than moored vessels is practical. It is recommended that PSOs monitor to a distance of 500 m, i.e., the greatest extent of Level B isopleths, during any Phase II pile driving.
- No marine mammal sightings occurred at low tide. It is generally accepted that harbor seals haul out on local ledges during low tide – a behavior that is well documented. For Phase II pile driving events, ORPC recommends two PSOs stationed on the installation barge with 180 degree visibility fore and aft. Further consideration should be given to reduced observations during low tide operations and seasons with minimal marine mammal activity.
Sea and Shorebird Observations
- Bird observations were not required by regulatory agencies; however, ORPC conducted surveys to determine any disturbance to a rookery (not active during pile driving) and potential bald eagle nesting areas. Results of bird surveys indicate minimal to no disturbance to birds in the project vicinity during pile driving. The value of future bird surveys during pile driving should be considered prior to Phase II.