BANGOR, Maine — A Syracuse University professor testified Thursday in a civil trial in U.S. District Court that the need for mercury remediation in the Penobscot River “is urgent.”

“I am very confident that cost-effective remedies could be done to improve the mercury levels in the Penobscot River,” said Charles Thurston Driscoll Jr. of the Department of Civil and Environmental Engineering at the university in Syracuse, New York.

Driscoll was the last witness for the Maine People’s Alliance and the Natural Resources Defense Council in their 14-year-old lawsuit against Mallinckrodt Inc. over the cleanup of mercury in the Penobscot River and Penobscot Bay attributed to the former HoltraChem plant in Orrington.

The jury-waived trial before U.S. District Judge John Woodcock began June 3 in federal court in Bangor.

Witnesses for Mallinckrodt began testifying Thursday afternoon.

The plaintiffs have said their experts believe the recovery time for the river is measured in decades, not years as Mallinckrodt has claimed.

The cost of remediation has been estimated at $130 million, according to court documents. A study of the amount of mercury in the river submitted in April 2013 recommended establishing a remediation program that could include the removing contaminated mobile sediments in the entire upper estuary and replacing them with clean sediments.

In a brief filed before the trial, Mallinckrodt contended the river is less contaminated and recovering faster than the study indicates. The brief also asserts there is no evidence of unacceptable risk to human health or of significant adverse effects on wildlife caused by the contamination. Their witnesses are expected to support that view.

The case stems from a U.S. Department of Justice order in 1986 that forced Mallinckrodt to develop a “corrective action” plan under the guidance of the U.S. Environmental Protection Agency after repeated pollution problems at the plant and concerns about contamination of the river were voiced. The HoltraChem plant closed in 2000 because of bankruptcy, which left Mallinckrodt as the only remaining former owner still in business.

The Maine People’s Alliance and the Natural Resources Defense Council Inc. filed the lawsuit against Mallinckrodt in April 2000 claiming that state and federal regulatory agencies were not doing enough to address mercury pollution problems in the Penobscot River below the plant, which sat on 235 acres.

The two environmental groups won a landmark legal victory against the company in 2002. The company was found responsible for the pollution that occurred between 1967 and the early 1970s, when tons of mercury were dumped into the river.

Since 2002, Mallinckrodt has funneled millions of dollars into the river study but also has fought to delay beginning the cleanup phase, according to the Maine People’s Alliance.

In May, concerns over elevated mercury levels found in lobsters prompted the Department of Marine Resources to close indefinitely a 7-square-mile area of the lower Penobscot River to lobster and crab fishing. The source of the mercury, the level of which is little more than what is found in canned white tuna, was traced to the defunct HoltraChem plant, according to previously published reports.

The trial will continue Friday and is scheduled to conclude June 27.

The is no timetable under which Woodcock must issues his decision.

BDN writer Nok-Noi Ricker contributed to this report.