PORTLAND, Maine — The Maine Supreme Judicial Court on Thursday affirmed a ruling requiring the former owner of the defunct HoltraChem plant in Orrington to proceed with a plan to clean up pollution from the site.

St. Louis-based Mallinckrodt Inc., the only former owner of HoltraChem still in business, had appealed a decision from Maine’s Business Court that upheld a Board of Environmental Protection cleanup plan. Mallinckrodt estimates the plan would cost $130 million to implement, according to court documents.

“Mallinckrodt US LLC is currently reviewing the Law Court decision issues today regarding the cleanup of the former HoltraChem site,” the company said in a statement Thursday. “We are hopeful that we can move forward cooperatively with the Maine DEP to discuss how best to implement the court’s decision.”

The closed HoltraChem factory, which operated on the banks of the Penobscot River from 1967 to 1982, produced 23,000 pounds of toxic mercury waste each year while developing chemicals for papermaking and other industries before the adoption of significant hazardous waste disposal regulations, according to court documents.

The BEP’s 2010 plan modified some parts of a 2008 cleanup order issued by the Maine Department of Environmental Protection, saying the company could leave three of the five landfills on-site after excavating the two other landfills and upgrading systems to prevent and detect pollution runoff into nearby groundwater sources.

Mallinckrodt appealed the BEP plan to the business court, and Judge John Nivison upheld the BEP order.

Mallinckrodt subsequently appealed to the Maine Supreme Judicial Court, which heard arguments in Portland on Feb. 11.

“The [DEP cleanup] order required Mallinckrodt to excavate material containing mercury and other contaminants from five landfills located on a site adjacent to the Penobscot River in Orrington, and to transfer the material to off-site landfills. The Board’s decision modified the Commissioner’s order, requiring that Mallinckrodt excavate only two of the landfills, and that it secure and monitor the others. We affirm the judgment,” Justice Andrew Mead wrote in the high court’s decision.

Maine Department of Environmental Protection Commissioner Patricia Aho applauded the ruling.

“The department is very pleased with the law court’s decision that affirms the order for Mallinckrodt to clean up the site,” she said. “It validates the department’s work on this matter.

“It is our hope that Mallinckrodt will stop using delay tactics through the court system and clean up the site,” she said. “The department stands ready and willing to work with Mallinckrodt on the long overdue remediation so the site can be returned to productive use.”

Mallinckrodt has reported spending tens of millions of dollars over the years removing metallic mercury, mercury sludge and contaminated storage tanks and buildings from the site.

Attorney Jeffrey Talbert, representing Mallinckrodt, told the high court justices in February that the BEP’s six-month appeal process did not follow any pre-established guidelines or procedures; included what amounted to expert testimony without adequate chances for the company to cross examine or respond; and allowed public outcry to bias the board despite scientific findings in Mallinckrodt’s favor.

The justices rejected those arguments in their decision.