A court will decide the best option to clean up a former manufacturing plant where tons of mercury had been dumped into Maine’s Penobscot River decades ago.

Maine’s highest court ruled in 2014 that the cleanup of the former HoltraChem Manufacturing Co. plant must be paid for by Mallinckrodt US LLC, the last vestige of the long-closed plant’s former owners. Mallinckrodt US LLC is a subsidiary of medical device giant Medtronic.

Engineering firm Amec Foster Wheeler is drawing up a set of options for how the site could be cleaned up. A spokeswoman for the firm says the recommendations must be submitted by March of next year.

The HoltraChem site was located in Orrington, about two hours north of Portland. Environmental groups have been calling for the site to be cleaned up for many years.