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Reviewed by: Dr. Ian Slayton

Last Update: January 5th, 2021

At the New York State Environmental Technical Working Group’s State of the Science Workshop on Wildlife and Offshore Wind Energy 2020 Session #4: Current Knowledge on Cumulative Impacts I, Ian Slayton (Physical Scientist, BOEM) explained the assumptions that were made when creating the Vineyard Wind 1 Offshore Wind Energy Project Supplement to the Draft Environmental Impact Statement published in June 2020.

Slayton works at the Bureau of Ocean Energy Management (BOEM) which is the organization responsible for managing the development of the nation’s offshore resources in an environmentally and economically responsible way. BOEM evaluates the potential impacts that proposed developments on the outer Continental Shelf (OCS) might have on ocean users, historical and cultural resources and the marine environment using a multi-phased process including the generation of environmental impact statements (EIS).

One of the challenges when considering the potential cumulative impacts of offshore wind energy (OWE) development is the level of information available for future development and uncertainty in the amount of future development that will occur. For this reason, all offshore wind leases off of the East Coast were considered for their potential for OWE development based upon state goals and previously announced projects. Leased areas with no associated project are assumed to be built out to the extent necessary for nearby states to meet their scheduled and anticipated OWE commitments.

Assumptions about details not yet known were made based upon the best available information. Frequently, assumptions are made based upon the most impactful case so that they can account for the highest possible impacts of OWE development, especially in the cumulative scope. Some of the assumptions that were made in the Vineyard Wind Supplemental Environmental Impact Statement are as follows.

Assumptions Made in the ‘Vineyard Wind Supplemental Environmental Impact Statement’ June 2020
Impact	Assumption
Timing of Future Construction	BOEM assumes that all announced project schedules will be kept with any delays resulting in a less rapid buildout and thus a reduced resulting impact.
Turbine Size	BOEM assumes the parameters and associated impacts of the largest turbine that is currently commercially available. In 2020, this is the 12MW turbine.
Vessel Availability	It is unclear if there will be an adequate number of vessels capable of supporting the number of overlapping construction schedules for wind farms. Vessel shortages would result in delays of project timelines.
Turbine Array Layouts and Density	All future developments in the Northeast follow a 1 nautical mile (nm) x 1 nm East-West grid. Other regions have similar structure capacity but region-specific spacing and orientation.
Foundation Types	BOEM assumes that all development in the existing lease areas within the Atlantic OCS will utilize fixed foundations due to the relatively shallow water depth. The considered impacts are consistent with those effects that are associated with the aforementioned 12 MW monopile turbines. In the event that future development utilizes jacket or gravity foundations, the net contribution to impacts is projected to be less than what is considered in this scenario. The selection of turbine structure is driven by oceanic and seabed conditions of the proposed turbine location. Read more about the effects that different turbine foundations have here.
Transmission Infrastructure	BOEM assumes that all transmission infrastructure challenges regarding cabling and interconnection points will be solved. Thus, any delays to infrastructure would delay the buildout or reduce the amount of development considered. The assumption that each development has its own transmission is also made meaning that, if regional transmission were to occur, the impacts would be less than in this scenario.