Glauconite poses challenge to another offshore wind farm project

Glauconite poses challenge to another offshore wind farm project

Another wind project on the East Coast may face challenges with turbine installation due to glauconite, a soil that crushes under high pressure. 

Preliminary geotechnical analysis for New England Wind, an Avangrid project, showed a risk of turbine pile foundation refusal in 50 of nearly 130 turbine locations, or about 40%, according to 2023 records obtained through a Freedom of Information Act request. 

In response to interview requests, an Avangrid spokesperson in a written statement said the company has a “well-informed understanding of the conditions in its lease area, including the presence of glauconite.”  

“Avangrid does not expect the presence of glauconite to result in any pile refusals in its New England Wind 1 project, but has considered the potential for pile refusals within its New England Wind 2 development plans,” said Avangrid spokesperson Craig Gilvarg. 

Records show BOEM asked Avangrid whether glauconite is a concern in what’s now the New England Wind lease. Avangrid responded in early 2023 that glauconite is present within the expected pile penetration depth and “may present some challenges,” but is “not anticipated to be a significant concern.”  

New England Wind is broken into two leases: New England Wind 1 (formerly Park City Wind) and New England Wind 2 (formerly Commonwealth Wind). New England Wind 1 is slated to start offshore construction as soon as 2027. 

New England Wind received approval from the federal government just last month to construct up to 129 turbines, and has bids currently under review by Massachusetts, Connecticut and Rhode Island to purchase the project’s power.

Per emails between BOEM officials last year, observations “indicate that the majority of planned foundation locations encountered glauconitic soils” for the New England Wind lease. Additionally, surveys showed layers of glauconite 5 to 20 meters thick within the lease. 

The thickness, depth, and concentration of glauconite all factor into the risk of refusal. Just because glauconite is present does not mean monopiles cannot be installed.

“Avangrid is confident that the technical options required to address glauconite within the New England Wind 2 project area are included within its Construction and Operations Plan,” Gilvarg wrote in the company’s statement to the Light. “These mitigation options available to the project will fully mitigate any risk associated with glauconite, and Avangrid does not anticipate the need to remove any positions within the lease area.”

Glauconite is a crushable, green mineral that is weaker and less predictable than sand and becomes clay-like when exposed to friction. When a monopile foundation for a wind turbine is hammered into the ocean floor, glauconite can break down and get stuck around the pile, keeping it from reaching required depths.

The mineral’s behavior poses a “significant risk” to offshore wind development, said BOEM, the federal regulator of offshore wind, in a paper last year. 

At a wind conference last month, a CEO said glauconite is one of the key challenges for offshore wind development on the U.S. East Coast. One attendee jokingly called it the “g-word.”

Last July, BOEM asked New England Wind to submit a memo and an updated pile driveability assessment, detailing where glauconite is present in the lease and how it may impact foundation feasibility, emails show. 

A report for the project’s final approval indicates that Avangrid plans to use monopiles or jacket foundations with three to four “pin piles” — about one-third the diameter of monopiles — for the first phase of the project (up to 62 turbines). The first phase borders Vineyard Wind, Massachusetts’ first offshore wind farm, which is generating some power but still under construction. 

As for New England Wind’s second phase (up to 88 turbines), Avangrid may use monopiles, pin piles or suction buckets for the turbine foundations. Suction buckets don’t go as deep and present an alternative when glauconite is present. Avangrid notes in its plans that more testing is required to see if suction buckets would be both a technically and economically viable option. 

Jacket pin piles are another solution for glauconite. They have a smaller diameter, and face less shaft friction and overall less resistance, compared to monopiles, explained a geotechnical consultant working on offshore wind projects. However, pin piles go much deeper in the soil. Additionally, the jacket structures used with them require more steel and would likely be more expensive than a monopile.

Pin pile foundation

Rendering of a jacket foundation with pin piles, which are much smaller in diameter than monopiles (but must be installed deeper), and can face less resistance with glauconite. Source: BOEM, New England Wind COP

Suction bucket foundation

Rendering of a jacket foundation with suction buckets, which are relatively shallow and can potentially avoid glauconite. Source: BOEM, New England Wind COP

The consultant said that if not for glauconite, most developers would likely go with monopiles because they would be cheaper. Solutions for constructing in the challenging soil will likely add to the costs of development. 

“I think there is a lot of concern both from [developers’] side, but also BOEM’s side,” the consultant said of glauconite. “They’re very aware this could delay development.” 

The consultant said developers’ estimates of pile refusal risk can change depending on the models they use. More accurate models informed by the behavior of glauconite could determine, for example, that fewer turbines face risk of refusal. 

Per New England Wind’s latest construction plan from February, the selection of foundations for the second phase is pending the outcome of a foundation feasibility analysis. Avangrid is part of an ongoing industry-funded research project into glauconite, which is assessing the geotechnical behavior of the mineral. 

A geotechnical engineer familiar with glauconite said the 5- to 20-meter layers found at the New England Wind lease are “not ignorable,” but added that several engineering solutions could address the challenge: a bigger hammer, thicker monopile walls, jacketed piles (a jacket foundation with pin piles), vibratory hammering, or suction bucket foundations. 

Another solution is drilling the monopiles to remove soil plugs. Avangrid’s construction plan states that based on soil conditions, the “drilling of monopiles could be required if a large boulder or monopile refusal is encountered.”

“The interior sediment will then be drilled out and deposited on the seabed adjacent to the scour protection material until the monopile is no longer obstructed. Monopile installation will then recommence until the monopile reaches target depth,” the plan states.

Drilling during pile installation in order to remove soil plugs and reach target depths could add to construction time and costs, experts say. 

Glauconite has already impacted planned development. In an example of “lessons learned,” as BOEM phrased it, the Sunrise Wind project rejected some proposed layout alternatives that could have minimized turbines’ impact on fisheries due to glauconite. 

BOEM declined comment on New England Wind’s glauconite conditions. 

BOEM has said glauconite formations are “abundant” along the continental shelf, and that wind developers will “inevitably” encounter the material during construction. 

The Light has confirmed that four leases on the East Coast are dealing with it: Empire Wind, Beacon Wind, Sunrise Wind and New England Wind. There may be more, but developers treat their geotechnical and survey data as proprietary. 

The only public data on glauconite’s presence in the United States is a decades-old, limited sampling. The U.S. Geological Survey is in the midst of identifying where the mineral is known to be, based on existing data. 

Email Anastasia E. Lennon at [email protected]

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