A pilot project depositing about 9,400 tons of sand in the lower Penobscot River to test its effectiveness in covering mercury contamination is likely to begin in mid-August.
Visitors to Orrington’s waterfront Picnic Park on River Road may see two barges working to spray sand over about 6.3 acres of intertidal flats in the cove, creating a cap 4-6 inches thick.
The project is a court-ordered step, years in the making, toward addressing industrial mercury contamination in the estuary that has had wide-reaching negative effects throughout the food chain and on human uses of the waterway. If successful, the method will likely be used to cap an additional 124 acres of intertidal flats.
The mercury 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.
The lingering mercury has led to a shellfish harvesting closure and consumption advisories for fish and some game. It travels up the food chain and has a range of toxic effects on people and wildlife.
The Maine People’s Alliance and the Natural Resources Defense Council sued Mallinckrodt US LLC, the last remaining party responsible for the plant, in 2000 over the contamination.
A 22-year court saga ended in a consent agreement outlining remediation work and ordering the company to pay $187 million for cleanup, with another $80 million in contingency funds.
Two trusts created by that decree, one governing the remediation work and the other funding smaller local projects, are overseen by a court-appointed trustee Greenfield Penobscot Estuary Remediation Trust LLC, affiliated with Greenfield Environmental Trust Group, Inc.
The decree requires capping 130 acres of intertidal flats with clean material, which will speed up the natural process of the river depositing new sediment on top of contaminated ones.
The method has worked elsewhere, but the Orrington pilot project just off of the waterfront park, in an area called East Cove 3, will show how well it suits the Penobscot and its unique characteristics, such as steep elevation changes, according to program manager Lauri Gorton.
“There’s no place like the Penobscot,” she said.
A state permit for capping the cove was approved in January. The trust expects a federal permit by mid-June.
Sand from local quarries will be mixed with water and pumped out to a barge, where it will be de-watered and sprayed a few feet above the river. That will allow it to settle gently in a fine layer. A second barge pulls the one carrying the equipment.
The project could begin in mid- to late August, depending on the federal permit and testing results to make sure the sand is clean. Work is expected to take two to four weeks depending on weather and tides.
People can watch from the park, and Gorton said the trust may offer site visits.
After that, the project will be monitored for 2-5 years for evidence that natural resources are recovering and the cap remains stable and clean. Monitoring will also focus on whether new sediment is deposited on the cap and how much, if vegetation re-emerges and small sand-dwelling organisms like marine worms return.
Mercury travels up the food chain through those organisms when they’re eaten by fish and birds, so the trust will sample how concentrations change in the cap and in organisms.
The state permit also requires monitoring for several rare plant species of special concern. The river is considered an “essential fish habitat” for Atlantic salmon, Atlantic sturgeon, and shortnose sturgeon as well.
Throughout, the monitoring will collect new information about the estuary, Gorton added.
“While we’re cleaning things up, we’re also adding to the body of knowledge about this portion of the Penobscot River,” she said.
If successful, the trust would need to apply for permits to cover the remaining acreage. Access to the water from adjacent property owners will be critical.
A contract for the pilot work has been awarded to Wisconsin-based J.F. Brennan, but the cost wasn’t immediately available Wednesday.
Sediments collect in coves because water moves more slowly there, according to Gorton, meaning particles in it settle on the bottom. Digging there would expose more mercury.
But in other parts of the river, mercury is still being moved around and it would be harder to keep a cap in place. The consent decree also requires removing contaminated sediment from some areas where those “surface deposits” continue to move.
When the tide comes in, heavier saltwater flows upriver along the bottom, trapping contaminated sediment from flowing downstream.
The trust plans to revisit 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.
