A team from the National Science Foundation and the International Ocean Drilling Program told the Nantucket Select Board it plans a summer expedition to core sediments and sample groundwater at three sites south and southwest of the island to study a subsea freshwater lens.

The researchers said the project proposes two boreholes at each of three sites — about 20, 27 and 43 miles from Nantucket — with coring to as much as 550 meters below the seafloor. Two boreholes would receive vertically deployed sensor cables left on the seabed for data collection, potentially for up to two years, the team said.

The expedition team emphasized its scientific goals: to determine how, when and whether meteoric (rainfall-derived) or glacial meltwater entered shelf sediments and how long that freshwater has persisted. “We're trying to understand how and when this freshwater was in place in sediments beneath the ocean,” said Brandon Dugan, identified as a hydrogeologist and professor at Colorado School of Mines.

Why it matters: Nantucket relies on a shallow sole-source aquifer for municipal water. Residents at the meeting asked whether the offshore freshwater the scientists will study could be connected to the island’s drinking-water aquifer or otherwise be contaminated by drilling. The project scientists said they are confident the offshore lens is not connected to Nantucket’s shallow municipal aquifer and noted prior onshore drilling and studies that found deeper freshwater lenses are isolated from the shallow drinking supply.

Permitting and monitoring: NSF staff said a draft Environmental Assessment (EA) was posted for public comment and that final permitting remains incomplete. Kristen Hamilton, an NSF environmental compliance officer, told the board a permit under Section 10 of the Rivers and Harbors Act from the U.S. Army Corps of Engineers is required and that the expedition could not conduct the permitted research activities until that permit is in hand. The team said it would coordinate with federal and state agencies and that reviewers have considered Endangered Species Act, Essential Fish Habitat and Coastal Zone Management Act requirements in their EA review.

Planned operations and discharges: The team described operations from a self‑propelled, three‑legged lift vessel (the transcript identifies the vessel as the “lift boat Robert”) that would set its legs on the seabed and operate a land‑style mobile drilling rig. The presenters said the coring tools are roughly 5.5 inches in diameter and that sediment cores are captured inside core barrels for analysis on board.

Regarding materials released to the water column, project staff told the board they would discharge two primary material streams: cuttings (sand, silt and mud from the borehole) and the biodegradable drilling mud (bentonite, seawater and starch). The team stated those discharges would be small — “less than one cubic yard per day” for cuttings and less than one cubic yard per day for drilling fluid — and said they expected local dispersion by currents. One member of the team said he would double‑check the EA wording after a public speaker cited a larger cumulative figure appearing in the draft document.

Public concerns and scientist responses: Speakers asked about potential harm to fisheries, seabed habitats, whales, sea turtles and birds, and whether detectable mud or marine life losses near Nantucket would trigger a halt. The project team said the EA includes monitoring and that, where an impact could be attributed to the expedition, they would stop. Scientists also stressed the program’s history of similar projects and argued uncased boreholes in soft marine sediments typically collapse naturally after abandonment; the team said past drilling records support that expectation.

Next steps and community access: Scientists said mobilization would begin from Bridgeport, Conn., and the expedition timeline would run roughly 90–100 days, with a start delayed from May 1 by a short mobilization lag. The team offered a project website, daily ship reports and social media channels for ongoing public updates and asked residents to use those channels for questions.

Ending: The Select Board did not take action on the presentation; members thanked the team and said the slides will be added to the meeting packet and that the town would relay community questions to the science team. Excerpts of the draft EA and final permit status remain the primary documents the town said it would rely on for formal environmental determinations.