Nantucket water official details PFAS contamination, treatment plans and offshore freshwater research

Mark Willett, a water-system presenter for the island, told the Nantucket Planning and Economic Development Commission on April 28 that the town's public water draws from a three-layer sole-source aquifer and outlined recent PFAS contamination and the town’s response.

Willett described the aquifer as “the upper, the middle, and what we call the lower aquifer,” explaining a semi-confining layer separates the upper and middle zones and that most public supply wells are screened in the middle aquifer. He said the town operates five supply wells (numbers 12–16), and that shallow wells 15 and 16 are in an upper aquifer zone used by many private wells.

The nut graph: The presentation focused on a PFAS plume near Tom’s Way that produced a detection of 55 parts per trillion in Well 15 — above the regulation Willett cited of 20 parts per trillion — and the town's plan to build an ion‑exchange filtration system, while also noting limits set by MassDEP on how much water the town may withdraw.

Willett said Well 15 was turned off after the detection and that the town is constructing an ion‑exchange resin treatment system at the Wires Valley well field. “We poured the first bit of concrete today,” Willett said, adding the system is being designed by ECT of Portland, Maine and will be piped into the town’s distribution and will be able to accept water from Wells 15, 16 and, if needed, Well 12. He said the system could treat “over a million gallons of water a day” and that media changes will probably be required every two to three years.

Commissioner Dave Iverson asked about effectiveness: “How effective are the PFAS filters? How much PFAS can they get out of the water?” Willett replied that both carbon and ion‑exchange resins are “very very effective,” and that the town selected ion exchange because it captures short‑chain PFAS better than carbon and can reduce concentrations “below detection limits.” He estimated replacement of resin media could cost in the “4 or $500,000” range each time and said spent media must be shipped under a hazardous waste manifest and either cleaned or replaced.

Willett said the town has been pursuing a deeper new source in North Pasture, a multi‑year permitting process that may be about a year from permitting and would yield the island’s largest producing well at more than 200 feet deep. He also explained that water‑withdrawal permit limits from the Massachusetts Department of Environmental Protection (MassDEP) are set on population estimates — he cited winter population of roughly 27,000 and a summertime allotment of 33,000 — and that any permanent increase in withdrawals to service newly extended mains or expanded service will require negotiation with MassDEP.

On broader research, Willett described an international scientific cruise that will drill three test holes on the continental shelf west of Nantucket and Martha’s Vineyard to test models predicting freshwater lenses beneath the seafloor. “This is the first group ever that’s going out to see if it’s true,” he said. He cautioned the research is strictly data collection, that any recovered lenses would lie in federal waters and that legal or operational questions about use or ownership would depend on jurisdictional and technical findings.

Commissioner Abby DiMolina asked whether grants or regional advocacy could help fund the system. Willett said the town had applied for grant funding and noted pending litigation and other funding sources are being pursued, though some recent grant applications were unsuccessful.

The presentation concluded with Commissioners asking about next steps and staff follow‑up; Willett said the treatment pad and piping work were underway with a hope to have filters operating before peak season and that the town will continue negotiating permit increases with MassDEP if main extensions to PFAS‑impacted areas proceed.

Ending: Willett asked the commission to consider grants and regional support and offered to meet with commissioners to review funding options as the treatment system moves into operation and longer‑term capital planning.