A 2017 image of Southern Cove in Orrington with the former HoltraChem plant, in the top right, and Penobscot Energy Recovery Co. in the bottom right, printed in a remediation report by environmental firms CDM Smith, Inc. and Anchor QEA. The circles indicate areas of mercury contamination in the Penobscot River. Credit: Courtesy of CDM Smith, Inc.

The recommended remediation of the Penobscot River estuary due to mercury pollution from a defunct chemical plant would cost between $246 million and $333 million, according to a report filed Tuesday in federal court in Bangor.

That is far higher than a previous estimated cost of $130 million for mercury removal.

The 172-page report was one of 15 filed by Portland-based Amec Foster Wheeler Environment & Infrastructure, Inc., in an 18-year-old lawsuit over mercury contamination in the river.

The firm’s recommendations include dredging and replacing the riverbed soil near the former Holtrachem chemical manufacturing site in Orrington with new soil. It also calls for the capping of much of Mendall Marsh and adding clean sediments to the tidal Orland River and the channel on the east side of Verona Island. In addition to those remediations, the plan calls for mercury levels in the river to be monitored for 25 to 45 years.

The Maine People’s Alliance and the Natural Resources Defense Council in 2000 sued Mallinckrodt, LLC of St. Louis, the owner of HoltraChem Manufacturing, when it filed for bankruptcy and shut down the same year the lawsuit was filed.

In 2015, U.S. District Court Judge John Woodcock ruled that Mallinckrodt was responsible legally for the cleanup of the river. The company already has spent millions to clean up the site itself.

“This is a huge victory for people who live along the Penobscot River and have spoken up over the years about this pollution,” Mike Tipping, spokesman for the MPA, said Wednesday.

Tipping also said that he could not comment on the specific recommendations because the organization still is reviewing them and comparing them to a report containing the alternative forms of remediation that were submitted to the court.

“This has been pending for a long time,” Tipping said. “It has been established that the Penobscot River can be cleaned up; the next question is how it will be cleaned.”

Mark Robinson, communications consultant for Mallinckrodt, said Wednesday the firm would challenge some of the recommendations, but did not say which ones.

“Mallinckrodt will challenge some of those recommendations the company believed will cause harm without measured benefits,” he said. “The company will challenge those that are unwarranted in light of limited harm posed by current conditions.”

The most expensive recommendation is the surface deposit dredging near the former HoltraChem site, the Frankfort Flats, the Orland River and the east side of Verona Island.

The goal of the lawsuit is the same it has always been — to make sure the river is cleaned up to a point where the mercury is no longer a threat to people, fish and wildlife, he said.

According to Tipping, scientists have said that it takes one teaspoon of mercury to contaminate a railroad car filled with fish.

“Over time, the HoltraChem plant dumped 12 tons of mercury into the Penobscot River,” he said.

A previous court-ordered scientific study found that 6 to 12 tons of mercury were discharged from HoltraChem into the Penobscot River between 1967 and the early 1970s.

Leaving the accumulated pollution as it is would mean waiting for several more decades for the mercury levels in the river to decrease enough to be considered safe — 30 years for much of the affected section of the river, and twice as long in Mendall Marsh, a 668-acre tidal wetland that branches off the west bank of the river between Frankfort and Prospect.

The build-up of mercury in the marsh prompted the state in 2011 to issue a health advisory about eating waterfowl hunted along the river between Orrington and Verona Island.

Three years later, state fisheries officials banned the harvest of lobster and crab between Orrington and Fort Point in Stockton Springs. In 2016, the ban was extended farther south, to the southern tip of Cape Jellison on the western side of the river and to Perkins Point in Castine on the eastern side.

Solving the problem is not as simple as digging up and hauling away the river bottom, however — even if it could be considered simple to dig up 20 miles of tidal river bottom. Because of the complexity and projected cost of cleaning the river, whatever plan ultimately is approved by the court is expected to include more than one method of removal or mitigation.

Part of the report recommends dredging more than 1 million cubic yards of sediment in subtidal (below the low tide line) and intertidal areas of the river. Of that amount, more than 200,000 cubic yards of polluted sediment would be removed from the intertidal area adjacent to and immediately downstream of the former HoltraChem facility.

Dredging will require containing the river’s sediments as they are churned up, to avoid dispersing the pollution even farther, which means erecting a containment barrier that can withstand the daily shifts in tide, scientists familiar with river pollution cleanup projects have said.

In Mendall Marsh the report calls for capping the marsh’s lower elevations, or about 50 percent of the 668-acre marsh area, with a minimum depth of three inches of fill. The added layer, which would help contain the mercury and reduce its exposure to wildlife in the marsh, would require approximately 191,000 cubic yards of clean sediment.

The engineering plan also recommends that clean sediments be introduced to the Orland River and the channel east of Verona Island to accelerate natural recovery, and that comprehensive long-term monitoring be done to evaluate how the broader river estuary responds to the mitigation efforts.

Woodcock said in 2015 that he would consider the following factors In evaluating the recommendations:

— Whether the proposed solution has been successfully attempted before or is innovative.

— The likely cost of the solutions.

— The length of time it would take to complete the recommendations.

— The likely effectiveness of the solution.

— Any potential environmental harm that may be caused by the proposed solution.

The reports filed Tuesday will be posted on the website that includes previous studies at www.penobscotmercurystudy.com. In addition to the website, meetings with stakeholders and in communities located in the affected areas will be held in the near future, according to the Communication and Community Involvement Plan.

A trial on the recommendations before Woodcock is set for October 2019.

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Bill Trotter

A news reporter in coastal Maine for more than 20 years, Bill Trotter writes about how the Atlantic Ocean and the state's iconic coastline help to shape the lives of coastal Maine residents and visitors....