Technical Report: Pile Driving Noise Survey

Editor's note: Rand's study of sound levels produced by sonar surveys in wind lease areas can be found at this link.

EXECUTIVE SUMMARY

Recent whale and dolphin fatalities on the Eastern seaboard, coupled with concerns about the acoustic impact of offshore wind farm construction, prompted an independent investigation to measure and assess underwater noise emissions from pile driving activities. Specifically, this assessment focused on the operations of the pile driving vessel Orion within the Vineyard Wind project area, with recordings taken in the waters southeast of Nantucket Island.

Key Findings:

• Pile driving noise, even with advanced noise-mitigation techniques, rivals the loudness and frequency range of seismic air gun arrays, with impulsive peak noise levels measured up to 180 dB over 1 kilometer away and RMS levels over 160 dB at over 3.3 kilometers.
• The standard 90-percent RMS metric utilized by the National Marine Fisheries Service (NMFS) underestimates the sound level experienced by cetaceans by as much as 6 dB, potentially cutting the protective distances in half and reducing marine mammal safeguarding zones by up to 75%.
• The continuous noise generated by vessel propulsion and dynamic positioning (DP) thrusters significantly surpassed the federal threshold for behavioral harassment, with noise levels exceeding 120 dB out to over 6 kilometers. Given federal agencies' concerns over the compound effects of continuous and impulse noise, this frequently overlooked issue in regulatory assessments constitutes a definitive risk of behavioral harassment to marine mammals, underscoring the need to reevaluate current protective measures.

Conclusion:

This investigation discovered a substantial underestimation of both impulsive and continuous noise levels by current regulatory standards, suggesting that the actual exposure to harmful noise levels from pile driving for marine mammals like the critically endangered North Atlantic Right Whale is substantionally greater than NMFS acknowledges in its existing protective measures. This indicates an urgent need to review and possibly revise NMFS monitoring protocols and mitigation strategies for pile driving to ensure adequate protection for marine mammals against both impulse and continuous underwater noise pollution. The findings detailed in this report underscore the need for immediate action due to the substantial underestimations uncovered by this independent investigation.

Recommendations:

• Immediate reassessment of RMS computation methods to more accurately represent the potential risk of pile driving noise to marine mammal hearing.
• Inclusion of continuous noise assessment from vessel operations in regulatory reviews, with a focus on managing combined noise levels to remain below NMFS thresholds for behavioral harassment during impulsive activities such as pile driving.
• Enhancement of protective radii and mitigation distances to shield marine mammals from the risk of behavioral harassment and auditory injury.