A “quagmire” of a Clean Water Act ruling that Justice Antonin Scalia wrote more than 13 years ago could now play a central role in the outcome of the U.S. Supreme Court’s most important environmental case this term.

In County of Maui v. Hawaii Wildlife Fund, lawyers for each side, including the United States as amicus, find support in Scalia’s plurality opinion in Rapanos v. United States. At issue is whether the federal clean water law requires certain permits when pollutants are conveyed from one source via groundwaters to navigable waters.