What site assessment activities will offshore wind developers perform as part of environmental review?

The Bureau of Ocean Energy Management (BOEM), (now the Marine Minerals Administration [MMA] [17]), the federal agency in charge of environmental review for offshore wind projects in the U.S. under the National Environmental Policy Act (NEPA), uses an unusual three-part process for environmental review. First, an Environmental Assessment (EA) is conducted for impacts related to site assessment activities — the studies done within the offshore lease area and along cable routes to identify sensitive habitats and species in federal waters, which are not well understood in our region. Then a programmatic Environmental Impact Statement (PEIS) will be completed that analyzes the cumulative environmental impacts from both the Humboldt and Morro Bay proposed offshore wind projects. Finally, each offshore wind energy area (WEA) leaseholder — RWE (1) and Vineyard Offshore (2) in Humboldt — will write individual Environmental Impact Statements (EIS) for each of their construction and operations plans.

The Coastal Zone Management Act ​​(3) requires federal actions that may affect a State’s coast to be consistent with that State’s coastal management program; in California, that means the Coastal Commission can impose conditions on BOEM (now MMA)’s activities related to offshore wind. In April 2022, the Coastal Commission adopted seven conditions of approval for site assessment activities (4), as well as “reasonably foreseeable” future development, including a vessel speed limit of 10 knots (11.5 mph) and requirements for protected species observers onboard offshore wind-related vessels to decrease the likelihood of collisions with whales and other marine mammals. Other conditions address entanglement risk for marine mammals, sharks, and sea turtles; collision risk to seabirds; and impacts to corals, sponges, and other invertebrates on the seafloor. Further conditions require engagement with California Native American Tribes, environmental justice and local communities, and fishing communities.

BOEM (now MMA) requires up to 5 years (5) of site assessment by offshore wind leaseholders prior to project design. First, the offshore wind companies submit (5) a site assessment plan (SAP) to them for review.  BOEM (MMA) will post final versions for RWE here (6) and for Vineyard Offshore here (7). To get a sense of what a final approved SAP looks like you can read the East Coast Vineyard Wind project’s SAP here (8).

During site assessment, the leaseholders will be performing many different surveys in order to gather as much information as possible about the site area. These surveys consider everything from the ocean floor to the air above the turbines in order to understand, to the extent possible, the ecosystems in which the turbines would operate. Surveys will also consider potential transmission export cables from the turbines to shore. The developers and the MMA will use the survey data to develop an environmental baseline against which they can measure any potential impacts of the projects. Some of the characteristics surveyed include wind speeds, wave activity, geology, coastal habitats, water quality, benthic resources, fisheries and essential fish habitat, marine mammals and sea turtles, birds and bats, archaeological sites, social and economic resources, coastal and marine uses, and air quality.

The first surveys developers will conduct are site characterization geophysical and geotechnical (i.e. imaging the seafloor and sediments) as well as metocean (i.e. measuring meteorological and oceanographic conditions) surveys to better understand the specifics of a site to inform project design decisions. Closer to (and after) construction, developers will conduct biological and environmental studies to better understand the wildlife, plants, and habitats specific to a site to be able to understand the potential positive and negative impacts of developing, constructing, and operating a project. Developers will also conduct desktop studies (i.e. socioeconomic analyses) to understand and describe the dynamics of how a project functions within a broader regional and community context.

Off the coast of Humboldt, leaseholder-driven survey work began in federal waters in early 2024, while surveys in state waters (within 3 miles of the coast) will be done in the future. The AXYS Humboldt Project Buoy (9) is currently measuring wave and wind speed in the Humboldt Wind Energy Area (WEA) and will be doing so for the next several years. This information may help inform design of future wind energy projects in the Humboldt WEA. 

The Humboldt Project LiDAR buoy. Source: Schatz Energy Research Center (10)

To map the seafloor within the offshore lease area, RWE contractor Argeo was selected (15) to deploy (11) a Hugin® 6000 (16) autonomous underwater vehicle (AUV) (12) in summer 2024 and 2025. As the name suggests, AUVs are unmanned and autonomous, navigating automatically and continuously, and using instruments on board to avoid crashing into the seafloor, deepsea rock formations, or other obstacles.

The Ecomapper Autonomous Underwater Vehicle (AUV), similar to Argeo's Hugin® 6000. Source: U.S. Geological Survey (13)

When in use, an AUV is brought out to sea on a boat and dropped in the water, where it dives down to approximately 130 feet above the seafloor. Once it is deep below the water’s surface, the AUV takes incredibly high resolution images of the seafloor, creating a detailed map of benthic habitats, rock formations, and anything else lying in wait at the bottom of the ocean. Each offshore wind developer can then use this information they have gathered to avoid sensitive areas when configuring the potential site layout or the potential route of the export transmission cable.

The survey work performed by the leaseholders will also be informed by survey work performed by independent researchers. For example, in 2022 a thermal tracker was deployed in the lease area to gather information about birds and bats in the lease area. The first analysis of that data, released in 2024 (14), found that 79% of the birds tracked flew below the swept area of the hypothetical turbines. Over the next several years, more data will be collected to better inform the analysis and develop a better understanding of what species are most at risk.

On April 24, 2024, BOEM (now MMA) released the Renewable Energy Modernization Rule (14). Several changes were introduced, including the elimination of the Site Assessment Plan (SAP) requirement to deploy meteorological buoys. As opposed to a SAP which had previously been required for future meteorological buoy deployment, developers will work through the U.S. Army Corps of Engineers (USACE) regulatory process to permit those activities in compliance with BOEM (MMA)’s Environmental Assessment (11). BOEM (MMA) is working on updating their website to reflect this information accurately.

​Additional surveys will be conducted in the future, and this page will be updated as new information becomes available.

References​​

1. RWE. (2024). https://americas.rwe.com/our-energy/offshore-wind/ 

2. Vineyard Offshore California https://www.vineyardoffshore.com/california

3. U.S. Bureau of Ocean Energy Management. (n.d.). Coastal Zone Management Act. U.S. Department of the Interior. www.boem.gov/environment/environmental-assessment/coastal-zone-management-act  

4. Greenson, T. (2022, April 7). Coastal Commission Votes to Move Forward with Humboldt Offshore Wind Exploration. North Coast Journal. https://m.northcoastjournal.com/NewsBlog/archives/2022/04/07/coastal-commission-votes-to-move-forward-with-humboldt-offshore-wind-exploration 

5. Morin, M. (2018, March 5). BOEM’s Environmental Review Process for Offshore Wind Energy Projects. U.S. Bureau of Ocean Energy Management. www.boem.gov/sites/default/files/renewable-energy-program/Environmental-Review-and-Compliance-of-Offshore-Wind-Energy-Projects.pdf 

6. U.S. Bureau of Ocean Energy Management. (n.d.). RWE Offshore Wind Holdings, LLC (OCS-P 0561). U.S. Department of the Interior. www.boem.gov/renewable-energy/state-activities/rwe-offshore-wind-holdings-llc-ocs-p-0561

7. U.S. Bureau of Ocean Energy Management. (n.d.). California North Floating LLC (OCS-P 0562). U.S. Department of the Interior. www.boem.gov/renewable-energy/state-activities/california-north-floating-llc-ocs-p-0562 

8. Vineyard Wind. (2017, November 22). Site Assessment Plan (SAP) Vineyard Wind Lease OCS-A 0501. U.S. Bureau of Ocean Energy Management. www.boem.gov/sites/default/files/renewable-energy-program/State-Activities/MA/VW-Site-Assessment-Plan.pdf

9. AXYS Technologies Inc. (2024). Humboldt Project Buoy. https://portal.axys-aps.com/platforms/P2067/ 

10. Schatz Energy Research Center. (2021, October 6). Offshore wind studies: Seabird 3D. https://schatzcenter.org/2021/10/seabird-3d/

11. Vineyard Wind. (2017, November 22). Site Assessment Plan (SAP) Vineyard Wind Lease OCS-A 0501. U.S. Bureau of Ocean Energy Management. www.boem.gov/sites/default/files/renewable-energy-program/State-Activities/MA/VW-Site-Assessment-Plan.pdf

12. National Oceanic and Atmospheric Administration. (n.d.). Autonomous Underwater Vehicles. NOAA Ocean Explorer. https://oceanexplorer.noaa.gov/technology/subs/auvs/auvs.html 

13. Central Midwest Water Science Center. (2020, October 13). Ecomapper Autonomous Underwater Vehicle AUV) [Image]. U.S. Geological Survey. www.usgs.gov/media/images/ecomapper-autonomous-underwater-vehicle-auv 

14. Schneider, S.R., Kramer, S.H., Bernstein, S.B., et al. (2024, April 24). Autonomous thermal tracking reveals spatiotemporal patterns of seabird activity relevant to interactions with floating offshore wind facilities. Front. Mar. Sci., 11. https://doi.org/10.3389/fmars.2024.1346758

15. Argeo. (2024, Jun 17). Argeo selected for RWE Canopy offshore wind project in Northern California. https://argeo.no/2024/06/17/argeo-selected-for-rwe-canopy-offshore-wind-project-in-northern-california/

16. Argeo. (2024). Hugin 6000. https://argeo.no/hugin-6000/

17. U.S. Department of the Interior. (2026). Department of the Interior Begins Transition to Marine Minerals Administration. https://www.doi.gov/pressreleases/department-interior-begins-transition-marine-minerals-administration