ORRINGTON — A settlement that is pending approval from a federal judge would require the former owner of a closed chemical plant in Maine to spend more than $180 million to clean up mercury contamination.

The settlement concerns the site of the HoltraChem Manufacturing plant on the Penobscot River that has been the subject of legal conflicts for more than two decades. HoltraChem’s one-time owner Mallinckrodt US, LLC of Delaware, would deposit $187 million into a trust fund to pay for the cleanup, and could end up adding up to $80 million more, the Bangor Daily News reported.

The Orrington plant operated from 1967 to 2000. HoltraChem filed for bankruptcy and shut down in 2000.

A federal judge ruled in 2015 that Mallinckrodt US, LLC was responsible for the cleanup of the river. Mallinckrodt owned the site from 1962 to 1982 and is the only former plant owner still in business.

The pollution was extensive. One study found that six to 12 tons of mercury were discharged from the plant into the river in the late 1960s and early 1970s.

Activist groups that sued Mallinckrodt US, LLC and attorneys for Mallinckrodt US, LLC both described the settlement as fair, the Bangor Daily News reported on Tuesday.