The step-by-step plan for cleaning up mercury in the Penobscot River

After years of mercury building up in the Penobscot River, a group of scientists and consultants are creating plans for how to extract, bury and dredge the chemical in what will be the largest cleanup of its kind in Maine.

They will start later this year with a pilot project to determine the effectiveness of capping mercury in the Penobscot River estuary, where the river meets the ocean. Capping adds several inches of sand over contaminated sediments to keep mercury away from fish and clean water. They are in the process of getting permits for the pilot and full projects, and permissions from local homeowners.

The Greenfield Penobscot Estuary Remediation Trust is responsible for carrying out the measures in a 2022 consent decree to clean up the river and support projects in harmed communities . The mercury was discharged into the river in the 1960s and early 1970s by the now-defunct HoltraChem Manufacturing Co.’s plant in Orrington. Plant owner Mallinckrodt US LLC will pay for the cleanup.

The measures cover three main remediation activities : capping 130 acres of intertidal flats between Orrington and North Bucksport, an area known as the Orrington Reach, with clean material; dredging sediments that move with tidal flow from the ocean; and identifying a remedy for contaminated sediment in the Orland River and the East Channel around Verona Island.

The court-ordered cleanup will cost $187 million, with another $80 million in contingent funding if more work is needed or for maintenance. Of the cleanup costs, $50 million will go to Orrington Reach , with $10 million in contingent funding. The money will be used to cap mercury-polluted intertidal sediments, primarily on the east side of Orrington Reach, with a layer of sand several inches deep. Intertidal areas are exposed during low tide and underwater during high tide. The goal is to keep the mercury separated from the water and wildlife, and the pilot project will help tell whether the capping will hold during harsh weather.

Mendall Marsh in Frankfort and Prospect has some of the most concentrated mercury levels reported in the world, according to Dianne Kopec, a faculty fellow in the George J. Mitchell Center for Sustainability Solutions at the University of Maine in Orono. Because marshes are sensitive areas with many plants, and they support a variety of wildlife and fish, the plan is to let the river cover the mercury naturally in normal movements of sediment over time, she said. Other possible remedies may be introduced.

Some $30 million will go to remedies for the heavily polluted Orland River and the channel east of Verona Island, where remediation may include a combination of removing contaminated sediments and capping.

Throughout the Penobscot River estuary, $70 million will go toward dredging sediments that move with the tides, with another $50 million available in contingent funds, according to the remediation trust. The remediation trust plans further studies on the best locations to remove contaminated sediments and how much to take out. The contingent funds can be used to pay for safe disposal in lined landfills.

Another $20 million will go toward so-called beneficial environmental projects in seven communities harmed by the contamination. They include a fishway at the Frankfort Dam, a recreational boat launch in Orrington and improving water quality management for the Penobscot Nation. Some of the beneficial projects money may be allocated to clean up Mendall Marsh.

Long-term monitoring of the cleanup area will cost another $10 million, plus $10 million in contingent funds if needed. The project will be monitored during work over the next decade and every three years after it is completed for 30 to 45 years , according to Cindy Brooks, president of the Greenfield Environmental Trust Group, which oversees both the remediation and projects in affected communities. The scientists will monitor mercury levels in the water, fish, birds, surface water, sediment and organisms that live in the sediment. The trust plans to share monitoring results on its website .

The remaining $7 million is for trust administration, with another $10 million in contingent funds if needed.

Lori Valigra is an investigative environment reporter for the BDN’s Maine Focus team. She may be reached at lvaligra@bangordailynews.com. Support for this reporting is provided by the Unity Foundation and donations by BDN readers.