The former HoltraChem Manufacturing Co. was situated alongside a gentle bend in the Penobscot River in Orrington, as shown here in 1997. High levels of mercury were detected in the rivers and lakes surrounding the site. Press Herald photo

The owner of a former chemical plant that dumped mercury into the Penobscot River must pay at least $187 million to remove the contamination in a resolution to a decades-long legal battle.

A federal judge on Tuesday approved the settlement calling for Mallinckrodt U.S. LLC to pay for remediation of mercury released by the now defunct HoltraChem plant in Orrington.

The plant discharged six to 12 metric tons of mercury from 1967 until the early 1970s, according to a previous court-ordered study. Environmental groups have long pushed for the remediation of the river.

“It’s long past time for Mallinckrodt to make it right, and this ruling will go a long way toward restoring the Penobscot, so people can go back to fishing, eating lobster, and enjoying this river,” Jesse Graham, co-director of Maine People’s Alliance, said in a statement.

The plant operated until 2000 and was located about 135 miles north of Portland, just south of Bangor. Maine People’s Alliance and Natural Resources Defense Council also filed a complaint about the mercury pollution in 2000.

The company’s financial obligations under the settlement will not exceed $267 million, court papers said.

The settlement states that Mallinckrodt will pay independent trusts that will fund and implement remediation of the river and nearby communities, Maine People’s Alliance said in a statement. The plant made chlorine bleach used by paper mills.

A federal judge ruled in 2015 that Mallinckrodt was responsible for the cleanup of the river. The company owned the site from the 1960s to 1982 and is the only former plant owner that is still in business.

The settlement means the parties in the case “believe that it is in their mutual interest to resolve their differences regarding remediation issues” and “move forward cooperatively and productively with remediation actions intended to reduce mercury exposures and accelerate the recovery of the Penobscot River estuary,” court papers state.

The company has already spent millions of dollars cleaning up the 235-acre facility site and paying for studies ordered by the court. Representatives for the company did not immediately respond to a request for comment about the settlement.