All proposed offshore wind energy projects described in a Construction and Operations Plan (COP) that are submitted to the Bureau of Ocean Energy Management (BOEM) for review must include assessments of potential environmental impacts resulting from project construction. See 30 CFR 585.627. Because underwater sounds generated from impact pile driving during foundation installation as part of the construction of offshore energy projects can impact marine species near the project area, BOEM’s environmental assessment is required to consider this impact producing factor. Specifically, two processes are typically performed: (1) noise impact and exposure assessments are conducted during the permitting phase, via modeling and analyses, and (2) ensonified areas are validated during the construction phase via sound field measurements.
The primary outputs from this modeling are the sound fields associated with the lessee’s project design envelope (PDE) and an estimate of “exposures” for each species of interest in a project development area. An “exposure” occurs when a particular individual of a particular species is exposed to sound above a given threshold. It is important to note that there may not be a one-toone relationship between modeled “exposure” and requested “take” under the Endangered Species Act (ESA) or the Marine Mammal Protection Act (MMPA). However, exposure modeling does provide an indication of the type and magnitude of impacts that may potentially occur for any given species. Allowable take is determined through consultation between BOEM and the National Marine Fisheries Service (NMFS) under the ESA and through the Incidental Take Authorization that may be issued by NMFS to the lessee under the MMPA. Lessees should consult with NMFS to ensure their modeling methods meet the needs of NMFS to assess take applications under the MMPA. The outputs of the sound modeling and exposure assessment are used by BOEM to inform the environmental impact assessment prepared under the National Environmental Policy Act (NEPA), biological assessments under ESA, and essential fish habitat assessments under the Magnuson-Stevens Fishery Conservation and Management Act.
These recommendations are specific to impact pile driving and are not comprehensive. Lessees should evaluate the effects of other noise generating activities associated with construction and operation of wind farms (e.g., vibratory pile driving, socket drilling, horizontal directional drilling, trenching, unexploded ordnance disposal, vessel noise, turbine operation, etc.) with the appropriate level of detail for the corresponding potential level of effect.
Sound field verification (SFV) measurements of pile-driving noise facilitate verification of the modeled distances to harassment thresholds and allow lessees, stakeholders, and regulators to determine the adequacy of certain mitigation and monitoring procedures implemented under the authorizations issued by regulators. The marine acoustic environment is, by its very nature, complex and variable. Therefore, the modeling should incorporate enough conservatism, and the verification enough samples, to ensure that the acoustic environment surrounding construction is within the PDE for the entire spatial and temporal scope of the construction activity.
This document comprises two sections. The first section aims to provide general recommendations to lessees as they develop the acoustic and exposure models of impact pile driving to be included with their COP submittals prior to issuance of a Notice of Intent to prepare an Environmental Impact Statement. BOEM recognizes that models are continually being refined and improved. As such, these recommendations are not meant to be prescriptive, nor restrain lessees to using a specific type of model. Instead, the goals are to ensure that key physical and biological factors are incorporated into the modeling and reported in the outputs, and that a uniform presentation of the modeling results aids BOEM with its assessments. The second section provides recommendations for SFV measurements to verify anticipated sound fields after COP approval. Such SFV measurements are typically incorporated into the conditions of COP approval. Because these projects and environments are complex, universal direction for every scenario is impossible to provide. Instead, this document describes the information that BOEM would find helpful in its assessment of environmental impacts. In addition to these BOEM recommendations, early coordination with both BOEM and NMFS is encouraged to ensure any additional information needs are satisfied.
This document provides guidance on several key concerns or issues that can typically arise during underwater acoustic modeling and SFV measurements. However, it is not an exhaustive list. Nothing written in this document is intended to override an lessee’s use of their technical or scientific expertise or experience. In fact, authors should be aware that guidance or references in this document may have been replaced by more current information and should always use the most current information and references.