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Offshore wind projects: Assessing the environmental impact

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An overview of rules and developments in Australia, Germany, Japan, Mexico, the UK and the US

Navigating environmental issues in offshore wind project development

Around the globe, opportunity is on the rise, but regulatory and political challenges persist

Throughout the world, many national and local governments are creating regulatory and commercial environments to encourage developers, lenders and investors to build, finance and invest in offshore wind energy. This has led to an upswing in the number of offshore wind projects being planned and built around the world. Renewable energy generated by offshore wind power is typically consistent with nations' climate change commitments under the Paris Agreement to reduce greenhouse gas emissions. However, offshore wind farms have unique impacts, which are addressed through environmental and natural resource policies and rules.

Governments in many of the key markets for offshore wind investment typically require the environmental and social impacts of a proposed offshore wind project to be assessed and mitigated. The complexity, sophistication and duration of the environmental impact assessment process varies across jurisdictions, and must be carefully evaluated by potential developers and investors. Project proponents also need to be mindful that in most jurisdictions, although to varying degrees, the environmental and social impact assessment
is subject to public scrutiny and comment, and can also be vulnerable to legal challenges.

This report offers an overview of key environmental risks raised by offshore wind projects in six key jurisdictions: Australia; Germany; Japan; Mexico; the UK; and the US. Offshore wind farms operate in many of these jurisdictions. In others, they are increasingly attractive because of higher offshore wind speeds and capacity factors, shallow ocean depths and supportive government policies. We summarize how regulators in these jurisdictions require project proponents to consider impacts to birds, bats, fish and marine mammals during the development process. We also assess how noise associated with the construction and operation of offshore wind projects must be addressed. Finally, we focus on the aesthetic considerations, decommissioning requirements and impacts to fishing, navigation and transportation that arise in the planning, construction and operation of an offshore wind project.


Offshore wind projects face challenges that are not addressed by the regulatory system established for onshore projects


A complex and sophisticated planning and approval process does not prevent opponents from raising environmental challenges—even after project approvals are awarded


Despite strong government support and growing capacity, a lengthy approval process may slow progress


With no offshore precedents, project proponents may find complexity, inconsistency and opportunity

United Kingdom

A global leader in offshore wind power capacity, the UK has seen rapid expansion in the sector

United States

As the offshore wind industry begins to take off, environmental impacts remain key concerns

Offshore wind power gains ground but faces environmental challenges

To maximize its potential, industry players will have to navigate an often-complex web of national, state and local environmental regulation

United States

As the offshore wind industry begins to take off, environmental impacts remain key concerns

14 min read

The development of offshore wind projects in the US has been hindered by environmental opposition to their visual effects, impacts on marine and other species, and interference with commercial activities, including tourism. Due to the all-encompassing environmental review and permitting process US projects undergo, opponents have been able to challenge them repeatedly and at multiple junctures throughout the process—in the case of one proposed wind farm, filing more than two dozen lawsuits. Despite this deterrent, the US offshore wind industry is gaining momentum. The first commercial offshore wind farm in the US became operational in 2016. Projects representing more than 25,000 megawatts (MWs) of planned generating capacity are currently under development, with projects generating 2,000 MWs expected to begin commercial operation by 2023, according to the federal Department of Energy. Still, to succeed in the US, offshore wind project proponents will have to continue to carefully review and manage environmental impacts.

An environmental analysis assesses the need for the proposed project, any alternatives, and the environmental social, economic and cultural impacts of the proposed project and alternatives.


The national environmental policy act

The federal National Environmental Policy Act (NEPA) is the principal US environmental law that typically dictates the environmental permitting and review process for offshore wind projects in US waters. Opponents often use the NEPA process to challenge wind projects. NEPA applies to projects that have a federal nexus, such as the need for a significant federal permit or the involvement of federal land, federal money or a federally managed transmission line. The NEPA process is public and, if triggered, can significantly delay a project.

Prior to permitting and construction, an offshore wind project subject to NEPA will undergo an environmental analysis called an Environmental Assessment (EA). Generally, an EA assesses the need for the proposed project, any alternatives, and the environmental social, economic and cultural impacts of the proposed project and alternatives. Based on the EA's results, the federal Bureau of Ocean Energy Management (BOEM) may then prepare a more rigorous assessment providing for public review and comment, and responses to substantive comments. This more rigorous assessment is an Environmental Impact Statement (EIS). BOEM acts as the lead agency for an EIS and coordinates with other federal and local agencies throughout the process to ensure all relevant federal and state requirements are considered before taking any action. In the US, each of the following key environmental impacts associated with a wind project typically arises during the NEPA process in both the EA and EIS.


Impacts to bird and bat species

US onshore wind project proponents often assess whether a proposed wind project will harm birds or bats, frequently devoting significant resources to analyzing whether birds are likely to be harmed in collisions with a wind farm's turbines. Over the past decade, US onshore wind project proponents routinely commissioned bird and bat species, and habitat surveys and conservation plans that aligned with federal government-issued guidance. The nascent US offshore industry has begun to follow suit.

Federal wildlife laws

Project proponents typically prepare these assessments and develop related conservation plans to avoid liability under the following US federal wildlife laws related to avian species: Migratory Bird Treaty Act (MBTA) protecting most migratory birds; Bald and Golden Eagle Protection Act (BGEPA) protecting bald and golden eagles; and Endangered Species Act (ESA) protecting species and habitats designated as endangered or threatened by the Fish and Wildlife Service (FWS), the US federal agency that manages fish and wildlife, including avian species.

These laws generally prohibit the unauthorized "take" of listed bird or bat species. The term "take" is defined broadly as to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture or collect. If a protected bird, for example, is harmed in a collision with a wind farm turbine, the wind farm operator could be subject to liability under one of these laws. However, FWS may allow a wind energy project an "incidental take" of an endangered or threatened species by issuing an incidental take permit. Wind project proponents often obtain these permits to protect themselves from future liability.

Prudent wind project developers frequently work with federal regulators during a project's pre-construction and construction phase to try to obtain a determination that the project is unlikely to affect any listed or endangered species or critical habitat; and that no permits are needed under the ESA, BGEPA or similar federal laws. This type of determination protects against claims for injunctions by private plaintiffs and reduces the likelihood that federal agencies will pursue enforcement actions in the event of a "take" of an endangered species in connection with a wind project.

To evaluate impacts to birds and bats, the FWS cooperates with BOEM throughout the NEPA review process, providing technical and biological information for use in the review to ensure that such species are considered during project planning. The ESA requires that a federal agency such as BOEM informally consult with FWS to ensure that its actions are not likely to jeopardize the continued existence of any endangered or threatened species.

If a proposed offshore wind farm may affect a protected avian species or critical habitat, BOEM must prepare a Biological Assessment (BA) to evaluate the potential effects of the proposed action on the endangered or threatened species or critical habitat listed (or proposed to be listed) under the ESA. If, based on the BA, the action is likely to adversely affect a listed species, formal consultation or conference with FWS is required.

Survey guidelines

In May 2017, BOEM issued Guidelines for Providing Avian Survey Information for Renewable Energy Development on the Outer Continental Shelf (ASG). These provide recommended timing, scope and technical suggestions for developers, but note that the avian surveys a developer is required to conduct may vary significantly depending on the scale and/or complexity of a proposed project, and the availability of existing data. BOEM recommends two annual cycles of boat-based surveys, traditional aerial surveys or high-resolution digital aerial surveys to determine spatial temporal distribution, abundance and behavior of avian species. If more data or analyses are needed to satisfy all state and federal environmental review processes, BOEM may require additional avian surveys before, during or after construction.

For example, Block Island Wind Farm, the only operating commercial offshore wind farm in the US, completed a three-year site-specific pre-construction avian and bat survey and committed to conducting additional post-application avian and bat surveys under a protocol reviewed and approved by FWS. Post-application surveys include bat acoustic monitoring (during construction), ship-based bird monitoring (two years during operation), nocturnal migrant collision monitoring (three non-consecutive years during operation) and avian radar monitoring (three non-consecutive years during operation).

While no laws or regulations specifically govern visual impacts in the US, the National Historic Preservation Act requires that federal agencies consider the adverse impacts of their actions on properties that may be eligible for or listed in the National Register of Historic Properties.


Visual impacts and the national historic preservation act

Because of their coastal locations, many proposed offshore wind farms in the US are near areas with high concentrations of recreation and tourism activities. Visual impacts to historic or culturally sensitive properties can be more significant if the proposed project is near a historic property or culturally sensitive resource. Cape Wind, one of the most highly publicized failed offshore wind projects in the US, was ultimately unsuccessful largely due to opposition from property owners concerned about adverse visual effects of a proposed offshore wind farm in Massachusetts' Nantucket Sound.

While no laws or regulations specifically govern visual impacts in the US, the National Historic Preservation Act (NHPA) requires that federal agencies like BOEM consider the adverse impacts of their actions on properties that may be eligible for or listed in the National Register of Historic Properties (NRHP). The NRHP includes districts, sites, buildings, objects and cultural resources. Further, BOEM must allow the Advisory Council on Historic Preservation (ACHP) an opportunity to comment, and must consult with state historic preservation offices and representatives of federally recognized Native American tribes.

In the Cape Wind example, it was determined that ocean views from historic Massachusetts landmarks would be adversely impacted by the proposed project, so the ACHP was invited to consult. Similarly, the US Department of the Interior was asked to consult due to anticipated impacts on views from Native American tribal sites in Massachusetts. Ultimately, Cape Wind's opponents could not use the federal environmental permitting process to halt construction of the project, and instead had to rely on other avenues, such as lobbying, to prevent the project from being awarded state-mandated energy purchase contracts and prevent the wind farm from moving forward. Nevertheless, the Cape Wind example demonstrates that BOEM is required to consult under the NHPA if a proposed offshore wind farm introduces visual elements that are out of character with the historic setting of structures or landscapes, and the historic setting contributes to a property's NRHP eligibility.

To determine whether the landscape can absorb the visual change resulting from a proposed wind project without significantly affecting scenic quality or viewer enjoyment, a project proponent generally prepares a Visual Impact Assessment (VIA). The VIA uses techniques such as distance modeling, visual simulations, and professional rating panels to quantify the potential effects and their impact on stakeholders. Ultimately, the VIA determines whether the threshold of acceptable visual impact will be exceeded and considers any measures that will reduce or mitigate visual impact, such as uniform design, lighting and siting.

Permitting timelines for Cape Wind, Block Island Wind Farm and Vineyard Wind

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Impacts on marine species

Offshore wind farms in US waters have the potential to impact a wide range of marine life, including scallops, quahogs, clams, finfish, marine mammals and sea turtles. As a result, US environmental law generally requires wind project developers to ensure that impacts to marine species are appropriately considered, site projects to avoid such impacts and implement other mitigation measures.

Applicable laws

While many marine species are listed as endangered or threatened and protected by the ESA, several additional laws intended to protect marine species also apply to offshore wind project development. The Magnuson-Stevens Act (MSA) governs marine fisheries management, fostering long-term biological and economic sustainability of federal fisheries. Among other things, the MSA protects marine and migratory fish species by establishing essential fish habitats (EFHs)—protected areas such as coral reefs, kelp forests, bays, wetlands and rivers necessary for fish reproduction, growth, feeding and shelter.

The Marine Mammal Protection Act (MMPA) protects all marine mammals, including whales, dolphins and seals, by preventing their killing or harassment. If a proposed wind farm may result in harassment of a marine mammal protected by the MMPA, the project proponent may submit an application to the National Marine Fisheries Service (NMFS) for an Incidental Harassment Authorization (IHA), which authorizes impacts to marine mammals that are no more than negligible, and that have no "unmitigable" adverse impact. An IHA is effective for up to one year.

The NMFS is the agency generally responsible for implementing these laws. As FWS does, NMFS cooperates with BOEM throughout the NEPA review process to ensure that impacts to marine species within its jurisdiction are considered. If a proposed wind farm may impact threatened or endangered marine species or a species protected by the MMPA that is within NMFS's jurisdiction, BOEM must submit a BA to NMFS assessing those potential impacts. If a proposed action may adversely affect an EFH, BOEM must consult with NMFS and, if necessary, submit an EFH assessment.

Survey guidelines

In July 2013, BOEM issued Guidelines for Providing Information on Marine Mammals and Sea Turtles for Renewable Energy Development on the Atlantic Outer Continental Shelf (MMSTG). These provide recommendations for developing information on marine mammals and sea turtles in compliance with BOEM regulations. The MMSTG note that the marine species surveys that a wind project developer is required to conduct may vary significantly based on regional biology, the scale and location of the proposed action and the availability of existing data. Nevertheless, the MMSTG provide recommended timing, scope and technical suggestions for wind project proponents.

BOEM recommends two annual cycles of vessel-based surveys or aerial surveys to determine spatial temporal distribution and abundance of marine mammal and sea turtle species, and two annual cycles of passive acoustic monitoring surveys to establish baseline ambient sound levels and presence of vocalizing marine mammals. To the extent possible, a proposed offshore wind farm should be sited to avoid important habitats, such as eelgrass, that support marine life. In addition, construction activities can be scheduled to avoid seasons associated with spawning or breeding, and a project proponent may use techniques and equipment that minimize disturbances.

Offshore wind project developers may conduct site-specific surveys before, during or after construction to provide additional assessment and mitigation of potential impacts. For example, Block Island Wind Farm agreed to conduct a four-year post-construction lobster survey to assess impacts to lobsters and shellfish, and a five-year post-construction trawl survey to assess impacts to finfish.

Cape Wind was ultimately unsuccessful largely due to opposition from property owners concerned about adverse visual effects of a proposed offshore wind farm in Massachusetts' Nantucket Sound.



To assess the noise impacts of a proposed offshore wind farm, a project proponent in the US will generally conduct in-air and underwater acoustic modeling studies. However, the noise impacts of offshore wind farms are largely unregulated by US federal law.

Some US towns and municipalities have noise ordinances, but operational noise from offshore wind farms is unlikely to violate these ordinances or be considered a significant impact for nearby residents because of the projects' distance from the coast. For example, the Town of New Shoreham, near Block Island Wind Farm, has a nighttime limit of 55 A-weighted decibels (dBA). Acoustic modeling studies for Block Island Wind Farm found that, in all modeling scenarios, sound levels at identified shoreline noise-sensitive receptors were likely to be below 25 dBA. In addition, Block Island Wind Farm is approximately three miles from the coastline, far closer than most proposed US offshore wind projects.

If construction activities associated with a wind project, such as pile-driving, are expected to generate short-term, temporary noise impacts at sensitive onshore receptors, a project proponent may elect to limit these activities to daytime hours to avoid running afoul of nighttime noise ordinances. However, noise impacts during construction are often more significant for marine species that are sensitive to pile-driving noise. The evaluation of noise impacts on marine mammals is generally performed as part of a biological assessment and submitted to NMFS for review along with the results of any underwater acoustic analysis. NMFS may then assess the significance of any noise impacts on marine life. To alleviate potential mortality, a project proponent may implement mitigation measures such as using fixed passive acoustic monitoring buoys, autonomous passive acoustic monitoring devices and noise reduction technologies. If necessary, the project proponent may apply to the NMFS for an IHA to authorize any potential exposure of protected species to disturbing noise levels.



Federal offshore leases issued by BOEM generally authorize offshore wind farms to operate for up to 25 years, although leases may be extended at BOEM's discretion. Projects are required to address decommissioning impacts in their construction and operation plans, and BOEM must assess these impacts in its review of each project. However, BOEM regulations also provide a number of requirements regarding the decommissioning of offshore wind farms, including financial assurance requirements and removal obligations.

Absent permission from BOEM, project proponents must submit a decommissioning application that includes all planned decommissioning activities, any resources or activities that could be affected by the proposed decommissioning activities, results of any recent biological surveys, mitigation measures that will be used to protect archaeological and biological resources and prevent unauthorized discharges of pollutants, and whether the area will be surveyed after removal to determine any effects on marine life. If the proposed decommissioning activities will result in any significant change to the impacts previously identified in a project's construction and operation plan submitted to BOEM, or require any additional federal permits, BOEM will be required to perform an updated NEPA analysis and other regulatory review as necessary.

Once approved, projects must complete decommissioning within two years of lease termination and either reuse, recycle or responsibly dispose of all materials removed. BOEM regulations require that projects remove or decommission all installations (including cables and pipelines) and clear the seafloor of all obstructions created by the project. All facilities must be removed 15 feet (4.6 meters) below the mudline.

Wind project developers may request that certain facilities remain in place following termination of the lease (i.e., if certain components or equipment, such as the onshore substation, remain fit for continued service). However, BOEM will consider potential impacts to the marine environment, impacts on marine safety and other factors in determining whether to approve such a request. Alternatively, a project may request that certain facilities be converted to artificial reefs or "otherwise toppled in place," subject to BOEM approval.

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