A tricky, sticky mineral that’s challenging offshore wind developers

Offshore wind developers are encountering an unexpected challenge on the East Coast seafloor: a crushable, green mineral called glauconite, sometimes precisely where they plan to install wind turbines. The mineral — which dates back to the age of the dinosaurs — is weaker and less predictable than sand, scientists say, presenting a new engineering puzzle for researchers and wind developers to solve.

Glauconite’s behavior poses a “significant risk” to offshore wind development, said a paper published this year by the U.S. Bureau of Ocean Energy Management, the lead regulator of offshore wind. It said glauconite formations are “abundant” along the continental shelf, and that wind developers will “inevitably” encounter the material during construction. 

At least two developers have run into the mineral in a total of three offshore wind projects — two south of Massachusetts and one south of Long Island, New York. In a document published last month, BOEM wrote that the geotechnical properties of the mineral make it an “extremely difficult material to build upon,” specifically for fixed-bottom wind turbines. 

Glauconite’s presence has already caused BOEM to reject proposed wind turbine layouts that might have minimized a project’s potential effects on marine life and the fishing industry. 

Offshore wind turbines will reach more than 500 feet above the ocean’s surface. They’re usually built on foundations driven more than 60 feet into the seafloor, but glauconite’s resistance to pile driving — which might lead to “pile refusal” — could make reaching target depths a bit harder. 

Glauconite could raise the construction costs of offshore wind projects and slow down project progress for an industry that’s already facing headwinds from inflation and supply chain issues. 

“Premature driving refusal can result in added costs which are orders of magnitude greater than those for onshore projects, and is a main risk factor in offshore developments,” said an industry-funded study, published last month. 

To address the challenge, five developers with projects planned along the East Coast are funding a yearslong industry project with a Norwegian firm to study glauconite’s behavior, develop scientific models, and devise methods to minimize uncertainty and risk.

The behavior of glauconite 

Layers of glauconite stretch from Massachusetts to the Carolinas and can be found on land and underwater. A trained eye can spot glauconite embedded in Gay Head cliffs on Martha’s Vineyard or dug up at a fossil site in New Jersey. 

Samples of the millions-years-old mineral sit in a repository at Rutgers University, in tubes, glass bottles, and cores. The cores, which capture millennia in mere meters, boast gradations of green, clumpy sediment: glauconite. There in the repository, marine geologist Kenneth Miller poured some from a small container onto a lab bench. 

“That’s a sand; you can see the grains,” he said. 

Then, with the butt of a glass container, he hammered the glauconite, pulverizing it without much effort into a powder, like silt or clay. He took a pinch of it and rubbed it between his fingers, now subtly covered in a green hue: “There’s no grains.”

Geologists and engineers describe glauconite as crushable, as Miller demonstrated. Rubbed between one’s fingers, it feels like sand — a tougher sediment that is better understood and often constructed on. But when exposed to pressure and friction, glauconite transforms. 

“You start with sand, but your process of trying to get through it, whether by hammering or drilling, makes mud, and that means you get stuck,” said Miller. 

Stuck isn’t a good thing, particularly when wind developers are hammering multi-million-dollar turbine foundations into the sea floor with specialized vessels that can cost hundreds of thousands of dollars a day to operate.

During offshore installation, the first turbine pieces to go in are the foundations. A common type is a steel monopile — a hollow cylinder that can exceed 30 feet in diameter. 

In a process called “pile driving,” a vessel equipped with a large “hammer” smashes the pile to its target depth through vibration or hydraulics. Because the piles will bear the weight of skyscraper-tall towers and 600-ton generators — and because they must withstand 30 years of waves and storms — engineers determine the depths they must reach in the seafloor to remain secure. 

Before any of that construction takes place, though, developers conduct geotechnical surveys and collect soil samples. That’s when glauconite has been turning up.

When glauconite is manipulated — in offshore wind construction, that would happen during foundation installation — it starts to crush, changing from sand-like to clay-like. 

“From a geotechnical perspective, that is like night and day,” said Zachary Westgate, associate professor of civil engineering at UMass Amherst and a researcher on the industry-funded glauconite project. Getting the monopiles into the seabed is key to installing wind turbines with fixed foundations, so if pile refusal occurs, it could present an added challenge.  

He framed it as an issue from a “pile drivability” perspective. After installation, glauconite’s behavior could end up being benign: “The industry has to sort of address this and reduce the uncertainty about installing their foundations.” 

Offshore wind developer Equinor has found glauconite at its two wind project locations, off Massachusetts and New York, respectively. 

At Equinor’s Empire Wind project, planned for the New York coast 15 miles south of Long Island, 22 of 71 planned turbine positions pose a high risk of pile refusal due to glauconite, according to the project’s final environmental review, released by BOEM last month. That means there’s a risk the developer could not install foundations to necessary depths in those locations.

Equinor has also found glauconite at its other lease, Beacon Wind, which sits south of Martha’s Vineyard, according to a company spokesperson. Equinor’s geological surveys and data evaluations for Beacon Wind are ongoing, but the company remains committed to its project timelines with New York and BOEM, the spokesperson said. 

Already, glauconite has scuttled some of Equinor’s efforts at working with the fishing industry over potential turbine layouts for its Empire Wind project. 

Equinor had discussed possible turbine positions with the Responsible Offshore Development Alliance, a coalition of fishermen and fishing companies. The discussions informed a proposed alternative for the Empire Wind project that would have eliminated seven turbines to allow more space for fishing vessels to pass through. 

The Massachusetts Office of Coastal Zone Management supported that alternative, in addition to another, in hopes of increasing access for fishermen, including New Bedford scallopers.

A different alternative, recommended by NOAA Fisheries’ Greater Atlantic office, would have removed up to six planned turbines near Cholera Bank, in an effort to minimize potential impacts to an important fish habitat. 

But BOEM concluded this September that the alternatives supported by RODA and NOAA Fisheries, respectively, were no longer viable due to the presence of glauconite. Because of the risk of pile refusal, BOEM concluded, glauconite reduced the number of “suitable positions” for turbines within part of the Empire Wind lease area to 49. Adopting the alternatives, the agency found, would preclude the developer from meeting energy contracts with the state of New York.

Ørsted, a developer that has several wind projects planned along the East Coast, found “various levels” of glauconite at its Sunrise Wind lease area, which is south of New Bedford and east of Long Island, according to a spokesperson. In a February 2023 letter to BOEM, Ørsted wrote that it anticipates pile refusal may occur during foundation installation at “several” of its 102 proposed turbine locations due to the presence of glauconite. The company said in its letter that it plans to propose an alternative layout of turbine locations. 

An Ørsted spokesperson told The Light that glauconite isn’t expected to affect the project timeline or its ability to meet agreements to deliver power to the states. Ørsted did not respond to questions of whether it has found glauconite at its other lease sites, and how many turbine positions might be impacted at its Sunrise Wind lease. 

Glauconite found in MA, NY projects

Glauconite can form over tens of thousands of years. The older it is, the darker it is — almost black; younger glauconite ranges in hues from a light jade green to greenish beige. It’s formed in part from fecal pellets and tiny marine organisms, but “it’s not all poop,” said Miller.

Glauconite can be around 70 million years old (or younger), yet researchers are finding some of it in seafloor strata that are less than 2.5 million years old. Miller says it could have been transported by water from glauconite beds on land. 

How much glauconite is present at future wind farm sites off the East Coast isn’t yet clear. Some projects might not run into it at all — or might find it in thin enough layers that it won’t cause issues during foundation installation. 

Developers are still conducting surveys and geotechnical analysis, and they treat the information they have gathered as proprietary. Public data that does exist on glauconite’s presence in the United States is decades old and only a limited sampling of the expansive continental shelf. 

Off Massachusetts, Beacon Wind and Sunrise Wind have confirmed the presence of glauconite. A spokesperson for SouthCoast Wind said geotechnical surveys have been completed of its lease area, but the analysis has not. 

Avangrid, co-developer of the Vineyard Wind farm now under construction, did not answer the question of whether it has found glauconite at any of its East Coast lease sites. 

An Avangrid spokesperson said the company is considering different foundation types and installation methods to “account for different types of seafloor conditions in our lease areas.” The spokesperson said the company is collaborating with industry partners to “advance the collective understanding of glauconite and its potential influence on offshore construction.”

A spokesperson for Attentive Energy, which holds an offshore wind lease off the New Jersey coast, acknowledged that glauconite is of “regional concern” along the New Jersey and New York coasts — likening it to concern over boulders in New England. The spokesperson asserted that the presence of any glauconite won’t affect the project’s ability to meet its power-generating capacity.   

Attentive Energy could turn to several mitigation measures if glauconite is discovered, the spokesperson said, including alternative turbine foundations (instead of a monopile) or installation methods. 

Government seeks better grasp on glauconite 

The federal government, which leases parts of the seafloor to wind developers, is also trying to get a better grasp on glauconite. A 2017 BOEM report identified the Atlantic Outer Continental Shelf as a “frontier.” There, “little information exists about the geologic conditions and how those conditions may impact development of offshore wind farms,” the report read.

“There are no experts on the topic,” a BOEM official wrote in an early 2023 email about an upcoming glauconite meeting to the agency’s renewable energy chief, Karen Baker. 

Glauconite is presenting apparent difficulties for NOAA Fisheries — a federal agency that works with BOEM to review offshore wind projects.

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In a letter this year to BOEM, NOAA Fisheries said information on glauconite was a missing piece in the agency’s ability to fully evaluate potential environmental impacts of the SouthCoast Wind project.

“We understand that the presence of glauconite is creating construction feasibility issues for some projects,” wrote Mike Pentony, a regional administrator for NOAA Fisheries’ Greater Atlantic office, “and the collection of geotechnical cores necessary to identify these constraints is occurring late in the process.”

Cores and other geological data are collected by the developer through surveys. If the surveys are not conducted prior to the agency’s environmental analysis, “we consider that to be ‘late in the process,’’’ said a NOAA Fisheries spokesperson in a statement to The Light. “Changes to the proposed action at that point in the environmental review may cause delays.”

BOEM, through a spokesperson, did not respond to a series of questions about glauconite — including where it is found on the outer continental shelf and how many offshore wind projects have encountered it.

The spokesperson said by email that the wind industry is studying measures to mitigate pile refusal in glauconite, and that BOEM will evaluate proposed mitigation measures as the agency’s project reviews continue. 

In 2021, the Norwegian Geotechnical Institute (NGI) started studying glauconite with wind developers. As of 2023, Ørsted, Equinor, RWE, Attentive Energy and Avangrid are participants of this joint industry project, called “Piling in Glauconitic Sands.” The five developers have at least a dozen projects combined slated for construction along the East Coast. 

Together, the developers have invested about $4 million in fieldwork, onshore pile driving tests, and laboratory tests to understand how glauconite will behave during turbine installation and longer term, according to researchers working with NGI. 

“Glauconite is definitely something that we need to better understand, so that we have more alternatives, so that we don’t eliminate turbine positions that may be actually installable after all,” said George Hagerman, offshore wind techno-economic lead at the National Renewable Energy Laboratory. “The more turbine positions that are geotechnically viable, the better, because it gives everyone more flexibility.”

Hagerman, who is reviewing data on glauconite for BOEM, said it’s in everybody’s interest to get a better handle on the material: “Once you’ve signed a lease, you can’t go outside that lease, and so you want to be able to use as many turbine positions in that lease as possible, or at least have them available for tradeoffs. 

“It’s a win-win for the environment, a win for the developers, a win for all the stakeholders if we can find ways to use turbine positions that have glauconite,” he said, “either by finding an alternative foundation or foundation installation method, anything that would allow us to have to not write off those positions.” 

Researching toward a solution

Engineers have encountered other challenging materials on the ocean floor before, like carbonate soils off the Australian coast (which caused the opposite issue — piles would fall into the collapsing sediment). They’ve figured out ways to construct on those sediments. 

Glauconite is not an entirely novel material for engineers, who’ve constructed on it in England and Belgium. “Glauconite sands have been successfully monopiled in Europe, but the concentration in European locations offshore is not as great as the glauconite concentration at U.S. sites,” said Hagerman.

Reporting on pile installation in Belgium where glauconite was present, researchers with Ørsted wrote in a recent conference paper that while the piles were installed to their target depths, “installation was time consuming, and a high number of blows was required.” 

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Proserpine Peralta, a geotechnical engineering manager with the firm Fugro, says that if a monopile gets stuck in glauconite, a larger (and likely more expensive) hammer will be needed. She recommended developers predict and plan for this risk before installation, as it could cost them millions more to address the pile refusal with either a bigger hammer or removal of the pile. 

Current predictions show that in some cases, available hammers may not be sufficiently strong to drive the piles to their target depths, due to glauconite layers, among other factors in the soil, Peralta said. 

Fugro is working on a solution that would involve drilling the glauconite clog out of the hollow monopile. After drilling, driving would recommence. In simpler terms: “drive-drill-drive.”

Don DeGroot, a professor of civil engineering at UMass Amherst and researcher on the developers’ project, said he is confident the industry will figure out this challenge with time.

“The geoscientists have done a lot of work on [glauconite], but I think it’s fair to say not a lot of engineering research has been done on it,” he said. “It’s nice to have the wind industry kickstart this interesting path.”

Developers and engineers use models to predict how soil will behave during construction, he explained, which in turn informs project design. Models for sands and clays are well-established, but a comprehensive model for glauconite needs to be developed (something the NGI project is working toward now). 

Pending more funding, the NGI project plans to start another phase of research.

“It’s all a question of risk and money, but there’s a lot of smart people in the offshore wind industry, and they have a ton of experience in Europe,” DeGroot said. “I’m very confident this is all going to be taken care of, and it will be looked back upon as a really interesting opportunity to apply engineering research to a practical project.”

Email Anastasia E. Lennon at alennon@newbedfordlight.org. 

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