A pilot project beginning in Orrington this week will spray about 9,400 tons of sand over the Penobscot River estuary, testing a method that could eventually cover 124 more acres of tidal flats contaminated with mercury decades ago.
Two barges will be located in the river for the next two to four weeks to scatter sand over about 6.3 acres of tidal flats, creating a cap 4 to 6 inches thick over an area called East Cove 3.
Equipment will be visible from Orrington’s Picnic Park for about two hours around high and low tide each day, depending on the weather.
It’s the first major on-the-ground work to clean up industrial contamination that has had wide-ranging negative effects on the food chain and human activity in the estuary, following a 22-year court battle over cleanup responsibility. If this project proves successful, the same method could be used to cover dozens of acres of contaminated coves in Orrington and North Bucksport.
This month’s work aims to show that the “thin layer cap” will remain stable, reduce mercury exposure in mudflat sediment and create a clean environment for organisms, according to the group conducting it. It’s designed to speed up the natural recovery process in the tidal river, which is slowly depositing new sediment on top of the mercury.
The contamination stemmed from the now-defunct HoltraChem plant in Orrington, which illegally discharged between 6 and 12 tons of the toxic metal in the river in the late 1960s and early ’70s.
Lingering mercury has led to a shellfish harvesting closure and consumption advisories for fish and some game. The metal travels up the food chain and has a range of toxic consequences for people and wildlife that ingest it.
The Maine People’s Alliance and the Natural Resources Defense Council sued Mallinckrodt US LLC, the last remaining party responsible for the chemical plant, in 2000 over the contamination. 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 smaller local projects in surrounding communities. Each is overseen by its own court-appointed trustee affiliated with Greenfield Environmental Trust Group, Inc.
The decree required capping 130 acres of tidal flats with clean material, such as the method being tested now.
Sediments collect in coves along the tidal river because water moves more slowly there, project manager Lauri Gorton said in May, meaning particles settle on the bottom. Digging there to remove the contamination would likely expose more mercury, hence the work to cover it.
In other parts of the river, mercury is still moving around as heavier saltwater flows up the river bottom when the tide comes in, trapping contaminated sediment and keeping it from moving downstream. It would be harder to keep a cap in place in those areas, and the consent decree also requires removing contaminated sediment from some places where these “surface deposits” are still active.
The remediation trust plans to revisit the sites this year to confirm the deposits are still present with high levels of mercury and gather information for removal plans. Permit applications would follow for that work, which is unlikely to start until at least late 2028.
The current pilot work is contracted to Wisconsin-based J.F. Brennan Company Inc., which has a patented system for gently spreading sand with a broadcast sprayer so it settles naturally through the water. One barge will hold spreading equipment, the second an excavator used to move it.
The cove will be monitored for three to five years to show that the cap is still stable and new sediment is being deposited on top to cover it. Monitoring will also see whether vegetation re-emerges and small sand-dwelling organisms like marine worms return.
Work isn’t expected to interfere with navigation or recreation outside of the capping area, according to the trust.
A drop-in event is planned at the park from 8:30 to 11:30 a.m. Wednesday, Aug. 26, for the public to talk about the project with trust representatives and see work underway. Scheduling is subject to change due to weather, tides or other conditions, the trust said.
A 24-hour hotline offers project updates at 207-352-3122, and an information kiosk is in place at the park.
