The lower Penobscot River is seeing a flurry of activity this week reminiscent of its industrial past as large barges laden with beeping, humming heavy equipment float just offshore of Orrington’s Picnic Park.
But this work is different – spraying about 9,400 tons of clean sand to cap about six acres of intertidal flats, covering toxic mercury sediment in a cove long contaminated by discharges from the former Holtrachem plant. If successful at reducing exposure in the estuary, the method could be repeated over 124 more acres in Orrington and North Bucksport in the coming years.
The project is the first major on-site work in a multi-pronged cleanup process that spent more than two decades in the court system and almost half a decade more in planning. While big questions remain about how well the capping method will work in the Penobscot estuary specifically, which the pilot is designed to investigate, the long-awaited activity has generally been received as a positive step locally.
“Get out of the courtroom, get out of the boardrooms and, you know, let’s put something to action, and see if it does work,” Orrington’s town manager, Chris Backman, said at the park Thursday morning. “And if it doesn’t work, you know, at least you tried. You know what doesn’t work.”
The cleanup has progressed through the courts and federal and state agencies. Municipal participation was mostly limited to offering office space and access to the cove. But the plant has been part of Orrington for a long time, Backman said, first as an employer and then as a vacant site at the center of legal proceedings, and the town supports the pilot.
The plant, which produced chemicals for papermaking and other industries, illegally discharged between six and 12 tons of the mercury in the river in the late 1960s and early ’70s.
That has led to a shellfish harvesting closure and consumption advisories for fish and some game. The heavy metal travels up the food chain with a range of toxic consequences for people and wildlife that ingest it. It has remained in place here partly because of the tides.
The Maine People’s Alliance and the Natural Resources Defense Council sued Mallinckrodt US LLC, the last remaining party responsible for the plant, over the contamination in 2000. Twenty-two years later, a consent agreement outlined remediation work and ordered the company to pay $187 million for cleanup, with another $80 million in contingency funds.
It also created two trusts, one governing remediation work and the other funding local projects in surrounding communities. Each is overseen by its own court-appointed trustee affiliated with Greenfield Environmental Trust Group, Inc.
The Department of Environmental Protection separately sued Mallinckrodt this week, alleging it had not made progress on cleanup at the former plant site – one of Maine’s most toxic – in years. That site cleanup is unaffiliated with the river remediation work.
The capping method being used in Orrington has proven successful elsewhere, but the pilot aims to show it will work with the Penobscot’s unique tides, elevation changes and currents, and that vegetation and organisms will rebound.
The idea is to speed up the natural process of the river depositing clean sediments on top of contaminated coves to effectively bury the mercury, while later work in other parts of the river would remove pockets of contamination, possibly by dredging. In coves, digging would likely expose more mercury, hence the cap.
“We wouldn’t be doing this if we didn’t know that it’s worked,” said Lauri Gorton, project manager for the remediation trust.
Two barges work side by side in the river. The “spreader barge” is controlled from a cab as a 12-inch pipeline, supported by floats, brings sand to it from a nearby staging area.
At the back of the barge, sand goes into a hopper that shakes water out, then moves down to a conveyor belt that carries it to two spinning discs spreading sand across the surface, where it can settle gently through the water column.
A larger guide barge helps pull the spreader along its length with a front end loader, then moves up and starts the process over again, heading toward shore as the tide comes in so the water level will be high enough to keep it afloat. The capping is being conducted in lanes.
Down on the staging barge, just out view from the park, a front end loader puts sand into a hopper box, then a larger box where it’s mixed with river water to form a slurry pumped through the pipeline for a continuous supply.
The project was already about halfway completed Thursday, with six inches of sand covering the cove’s north end. The south end, at the edge of the park area, will be covered by about four inches. The crew currently aims to finish before Labor Day.
Workers periodically check the depth of the cap with a long pole sunk into the flat, and a survey boat takes elevation measurements.
Residents have generally been supportive and hopeful, Gorton said, though she’s also heard some “reasonable skepticism,” particularly about whether the cap will stay in place and how natural resources will recover – questions she said the trust shares and aims to answer through the pilot.
“Most of the people that are on the river appreciate the effort…I’d say the majority, if not all of them, have their fingers crossed,” Backman said.
Preparatory inventory work around the cove also revealed a fourth known rare plant species there, Atlantic mugwort, and generally has collected more information about the area and its natural inhabitants than there’s been reason to study before.
The clean cap could also make it possible to dig safely for shellfish in Orrington again one day.
Monitoring will continue for three to five years to evaluate the cove’s recovery, but once the sand has been spread, the cap “belongs to the river,” Gorton said. The trust won’t perform maintenance or try to keep it in place.
“This is a remedy that was designed to work with the river and Mother Nature,” she said.
The cap is currently visible in lighter layers at low tide, but the river is expected to deposit darker sediment over it again soon.
“My hope is that people are going to come and they’re going to look and they’re going to say, ‘I don’t really see anything,’ because that’s perfect,” Gorton said. “We aren’t leaving a monument, we’re leaving something that is going to become a part of the surroundings.”
