The Supreme Court says the U.S. territory of Guam can pursue a $160 million lawsuit against the federal government over the cost of cleaning up a landfill on the island.

The justices on Monday unanimously overturned a lower court decision that had said Guam had waited too long to pursue the claim.

The case before the justices involves a long-running dispute over the Ordot Dump on Guam. The lawsuit says the Navy built the dump during the 1940s and then deposited toxic military waste there before turning over control to Guam in 1950.

Guam operated the dump for decades. The U.S. has said Guam “vastly expanded” it and “failed to provide even rudimentary environmental safeguards.” In 2002, the government sued Guam over pollution from the dump. Guam ultimately agreed in 2004 to close the dump and take steps to stop pollution from the dump, among other things.

In 2017, Guam sued the United States, arguing that it’s responsible for some of the costs of the cleanup, which Guam estimates to be more than $160 million. A trial court had allowed the lawsuit to go forward, but an appeals court had dismissed it.

In an email, Guam’s attorney Gregory Garre said: “We are thrilled with the Court’s decision in favor of Guam today, which paves the way for the United States to pay its fair share for the cleanup of the Ordot Dump.” The case is Territory of Guam v. United States, 20-382.