4 The record articles

Offshore Wind Farms & Air Permitting Challenges

Posted: May 4th, 2023

Authors: Joe S. 

The race towards the Biden administration’s goal of having 30 gigawatts of offshore wind online by 2030 has led to a flurry of projects aimed at helping the United States achieve this objective, with construction of one major 800-megawatt offshore wind farm underway and another set to begin shortly. However, before construction and operation of an offshore wind farm can commence, the Project must obtain dozens of permits and authorizations aimed at ensuring environmental resources are not adversely impacted by the wind farm.

One of the more unique requirements for an offshore wind farm is to obtain an air permit. Construction and operation of an offshore wind farm on the outer continental shelf (OCS) is subject to the Outer Continental Shelf Air Regulations (40 CFR Part 55). The OCS air regulations were promulgated in 1992 and were used initially to regulate offshore oil and gas activities. The OCS includes the area between state jurisdiction (3 nautical miles) to 200 nautical miles from shore. Most states have not been delegated Part 55 permitting authority so Projects subject to an OCS Permit deal directly with either the United States Environmental Protection Agency (U.S. EPA) or the Bureau of Ocean Energy Management (BOEM) depending on its geographic location1.

Sources subject to OCS permitting are defined as having air emissions that occur on vessels that are “permanently or temporarily attached to the seabed and erected thereon and used for the purpose of exploring, developing or producing resources therefrom” (see 40 CFR §55.2). Once an OCS source is required to obtain a permit, 40 CFR Part 55 requires that emissions from vessels that are servicing or associated with the operation of an OCS source must be counted as direct emissions from the OCS source. One unique wrinkle of 40 CFR Part 55 is that the regulations require that emissions from vessels traveling to and from the OCS source (and the equipment on those vessels) are then compared to major source thresholds to determine whether Prevention of Significant Deterioration (PSD) or Nonattainment New Source Review (NNSR) (depending on the location) apply. The vessels involved in the construction and operation of an offshore wind farm have emissions of criteria pollutants that can be in the thousands of tons and the potential for exceeding the PSD or NNSR thresholds is quite high.

If project emissions are greater than the PSD or NNSR thresholds an offshore wind farm must prepare a permit application that complies with the “corresponding onshore area”2, permitting requirements. This often includes documentation of lowest achievable emission reductions (LAER), emission offsets (in non-attainment areas), and a PSD modeling analysis that demonstrates compliance with both Class I and Class II increments as well as the National Ambient Air Quality Standards (NAAQS).

There are several logistical challenges associated with construction and operation of an offshore wind farm that are critical to consider when seeking an OCS air permit. The first centers on the use of a project design envelope concept. Because of the construction lead time and because the offshore wind industry is evolving rapidly, wind farms typically seek to permit a range of design parameters  (ex. this could include elements such as turbine type or number of turbines) that allow them the maximum flexibility to both construct and operate the wind farm. The implications of this for air permitting are typically that air emissions are overstated to allow for this additional flexibility within the OCS permit.

Another logistical challenge is that for some portions of the construction of the wind farm there may only be a few dozen vessels available worldwide capable of performing the work. Most of these vessels are foreign flagged vessels and because of the Jones Act are unable to go to ports in the United States. Wind farms are often competing for these vessels on a global scale, and the ability to modify a singular vessel to meet emission limits in an OCS air permit can be quite costly, result in significant delays to a project, and take one of these few vessels out of service while emission controls are installed.

If an offshore wind farm is in a nonattainment area for ozone, they would be required to obtain offsets for volatile organic compounds (VOCs) or oxides of nitrogen (NOx). Upcoming changes to the fine particulate (PM2.5) National Ambient Air Quality Standards (NAAQS) may create new non-attainment areas causing Projects to also have to obtain offsets for PM2.5. Offsets in many areas are severely limited and pose a significant challenge for the offshore wind industry moving forward.

Air Modeling Challenges for Offshore Wind

Construction and operation of an offshore wind farm also poses challenges for air dispersion modeling. The EPA preferred model for modeling overwater conditions is the Offshore Coastal Dispersion Model (OCD) developed in the 1970’s which lacks many of the modern-day advances in air dispersion modeling incorporated into the current generation of air dispersion models. A project can avoid modeling emissions from construction if it can commit to construction of the offshore wind farm in under two years and that construction won’t impact a Class I area.  Air dispersion modeling is further challenged by U.S. EPA’s definition of ambient air which may requirement the placement of receptors as close to 25 meters to a vessel. A project is also required to prepare an air quality related values analysis for impacts on Class I areas.

Based on the above, demonstrating compliance with the PSD Class I, Class II, and NAAQS can be complex and can come at a cost of a reduction in the project design envelope concept. An additional challenge is that as more offshore wind projects are proposed, agencies are asking for cumulative impacts that consider the cumulative impact from all nearby projects. Many of these projects are directly adjacent to each other and may have similar construction timelines.

How can ALL4 Assist?

Offshore wind farms are subject to a litany of permitting requirements beyond an OCS air permit that it must obtain prior to construction, and an OCS permit is one step of many to complete the construction. In addition to an OCS air permit, a wind farm must also obtain permits from the BOEM, the Army Corps of Engineers, US National Marine Fisheries Service, the US Coast Guard, the Federal Aviation Administration as well as coordinate with state agencies and stakeholders. ALL4 staff can assist with many of these permits and can help develop strategies to approach all phases of permitting for an offshore wind farm. Reach out to Joe Sabato at jsabato@all4inc.com for more information.


1OCS sources located in the Gulf of Mexico west of 87.5° longitude (i.e., offshore TX, LA, MS, AL) and areas offshore the North Slope of Alaska, which are under the authority of BOEM and the Bureau of Safety and Environmental Enforcement.

2Corresponding onshore area means, with respect to any existing or proposed OCS source located within 25 miles of a State’s seaward boundary, the onshore area that is geographically closest to the source or another onshore area that the Administrator designates as the COA, pursuant to 40 CFR Part 55.5.


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