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Just north of Pope’s Island in the New Bedford Harbor, a giant, 12-acre pit sits at the bottom of the ocean, covered by layers of sand and rock. Filled with contaminated soil, the pit is meant to exist indefinitely, gradually collecting more sediment until it grows into a pronounced lump on the ocean floor.
The pit contains soil contaminated with PCBs, the manufacturing byproduct that has leaked into the fish in New Bedford’s harbor and prompted a decades-long federal cleanup effort.
Since 2003, the U.S. Environmental Protection Agency has used these pits — officially known as confined aquatic disposal (CAD) cells — in New Bedford Harbor to store tainted sediment that would otherwise get dried out and shipped out-of-state.
This past year, New Bedford and Fairhaven completed a seventh CAD cell as part of a project to restore harbor health and expand the city’s working waterfront.
The project involved dredging up sediment from the harbor floor, storing contaminated soil in the new CAD cell, and using the non-contaminated soil to build a harbor extension: the newly completed North Terminal. The project officially wrapped in December 2024, but the city announced its completion last month. A grant from MassWorks funded nearly 80% of the $36 million project.
Gordon Carr, executive director of the New Bedford Port Authority, which oversaw the project, called the dredging efforts a “win-win” for public health and for the fishing, cold storage, and other waterfront industries dependent on the harbor.
“Doing it on their own would have been prohibitively expensive,” Carr said. “They just wouldn’t have done it.”
Dredging deepens and widens parts of the harbor floor, allowing captains to dock larger ships and expanding the harbor’s commercial capacity. The most recent phase of the project dredged around seven terminals, mainly in the southern section of the harbor, cleaning approximately 3 million square feet of the harbor floor.
The dredging also allowed the city to remove 500,000 cubic yards of sediment that does not meet the level of contamination necessary for remediation by the EPA, but could nevertheless pose a risk to human and sea life.
Since the early 1990s, the EPA has worked to remove PCB-contaminated sediment from New Bedford’s harbor by dredging it up, sifting it from clean sand, squeezing out excess water and eventually transporting the waste to a landfill in Michigan. Over time, the EPA began storing less-contaminated sediment in CAD cells underwater to save money, site project manager Chris Kelly said — the same practice the city continues today.
The process is relatively simple, Kelly said. Excavators clear the sand and gravel from the harbor floor, dig a hole, and fill that hole with the contaminated soil. The cell is then covered by silt, sand, and armor stone.
Kelly said he didn’t anticipate the CAD cells getting damaged or leaking contaminated sediment at any point. Still, earlier this year the EPA sent a diver to inspect a CAD cell that appeared to have been struck by a vessel. According to a report of the inspection reviewed by The Light, some stones surrounding the container had been dislodged, but the team found no evidence of leakage or damage to the container itself.
“Our assumption is that it was a vessel strike, but no captains reported running aground in the harbor,” Kelly said. “We had to figure it out ourselves because the person didn’t self-report.”
Ships would not face any penalties for accidentally striking or damaging a cell, Kelly added.
The EPA completed its remediation of the harbor in 2024 and is now in a monitoring phase, Kelly said. Still, federal officials discourage New Bedford residents from eating “unlimited” amounts of seafood caught in the harbor due to potentially high levels of PCB.
“The focus (now) is going to be on educating people about consuming fish in the harbor and what our recommendations are,” said Aaron Shaheen, the EPA’s community involvement coordinator on the project. “We want people to fish, but we also want people to be safe in consuming it.”
The City of New Bedford has already begun planning the next phase of dredging, which includes excavating additional spots in the harbor to fill the rest of the CAD cell to capacity. The city is also expanding Leonard’s Wharf with additional dredged material, with construction to be completed by October 2026.
In the meantime, the Port Authority will begin gauging interest from prospective business partners for the new North Terminal. For now, the site hosts a slew of commercial fishing vessels displaced by the Leonard’s Wharf construction.
Carr said the city will consider applications based on economic benefit to the community. While he said he is open to nearly all ideas, a few possibilities might give him pause.
“If somebody wanted to bring in trash, for example, don’t bother,” Carr said. “We’re not doing that… If they wanted to just store salt, for example, which you see in Boston, that needs a lot of space and needs water and doesn’t create jobs. That’s probably not our priority. We want to see this active. We want to see this as a real economic engine for the waterfront.”
Email Brooke Kushwaha at bkushwaha@newbedfordlight.org.
Editor’s note: This story was modified on Thursday, Sept. 4, 2025, to clarify that not all of New Bedford’s seafood is contaminated, just fish caught in the harbor.
Thank you for the article on the environmental and operational benefits of the New Bedford Harbor Dredging. However the matter of fact statement in the third paragraph about the EPA using the confined aquatic disposal cells since 2003 belies the significant efforts of local, state and federal officials led by then New Bedford Mayor Fred Kalisz to unlock the potential of the “state enhanced remedy” provision of the EPA Record of Decision overseeing the superfund cleanup of the harbor. Prior to the efforts the EPA planned on disposing the dredged sediment in a confined disposal cells along portions of the harbor. These disposal cells would not have had the capacity to support any marine industrial uses preventing development of freight, fishing , wind energy support, or the recent North Terminal expansion. While it’s gratifying to celebrate the success of the harbor dredging, it is equally important to recognize the foresight and efforts that led to that success.
So they dig a hole and place contaminated sediment in it. I missed the part regarding the material they removed to create the hole. What is it, and where did it go? Whack a mole or a shell game?
It would be great if they did more Air Quality testing and made the reports / results public. The last study was completed in June of 2017 and it identified New Bedford Harbor as major source of Airborne PCB’s. Here is the link to the article (https://www.bu.edu/sph/news/articles/2017/new-bedford-harbor-identified-as-major-source-of-airborne-pcbs/).
The study appears in the Environmental Science & Technology Letters and concludes the airborne PCB emissions were so high that researchers said the harbor was the single largest continuous source of airborne PCB’s ever measured from natural waters in the US or Canada.
With dredging still going on and materials being moved an Air Quality study should be completed and the results made public to reassure residents who are working or engaging in any activities near the river (walking, boating, or rowing) that it is safe to do so and this is no longer an issue.
I was surprised to read that the cad cell will eventually become a “lump” on the ocean floor! If it was recently struck by a vessel, why are there not navigational markers in place around the cell?