AUGUSTA — State officials are escalating action against a company they say has failed to clean up “the most contaminated site in Maine” after more than 20 years of lawsuits.

The Maine Department of Environmental Protection filed a formal complaint Tuesday in Penobscot County Superior Court against Mallinckrodt US LLC.

The state alleges that the company has failed to clean up the former HoltraChem site on the Penobscot River in Orrington.

The site “discharged to the environment tons of mercury and thousands of tons of mercury-contaminated brine-sludge, substances that are defined as hazardous wastes,” according to the lawsuit.

The facility made chemicals commonly used in the pulp and paper industry, according to DEP. It operated under various owners from 1967 to 2000.

The company did not respond to a request for comment.

The suit says the facility covered about 235 acres near the river, 77 of which were affected by the production. The site included five landfills, a manufacturing facility and waste piles.

In the mid-1980s, the U.S. Environmental Protection Agency and the state began investigating the site and calling for remediation.

According to the suit, in 2000, the Maine People’s Alliance and the Natural Resources Defense Council filed a lawsuit against the company alleging that the company “discharged mercury from the site into the Penobscot River and that these discharges resulted in an imminent and substantial danger to public health and the environment.”

A court ordered the company to come up with a remediation plan.

A press release from DEP indicates that since 2023, the company has not made any progress toward remediation.

The latest lawsuit asks the court to remove contaminated soil and industrial sewer lines, assess civil penalties and require the company to comply with all DEP orders.