GordonDerr represented the Tulalip Tribes from 1989 to 2005 regarding the former "Big Flats Landfill" Superfund site on the Tulalip Reservation. The firm represented the Tribes in negotiations with EPA; the U.S. Department of Justice; the Bureau of Indian Affairs; the Department of Ecology; other federal, state, and local agencies; and hundreds of private parties regarding technical investigations, the evaluation and selection of cleanup alternatives, insurance claims, and global settlement negotiations. Keith Moxon was the Tribes' lead counsel in negotiating seven federal consent decrees settling CERCLA liability and resolving a claim for natural resource damages. GordonDerr negotiated a U.S. Department of Justice/EPA determination of the Tribes' immunity from CERCLA liability, a nationwide precedent regarding tribal immunity under Superfund.

In the course of this Superfund representation, GordonDerr successfully defended the Tribes in a federal court lawsuit under the Clean Water Act, which challenged EPA's and the Tribes' investigation and cleanup of the site under CERCLA and sought $1.8 billion in alleged "citizen suit" damages. The Tribes prevailed in U.S. District Court and also prevailed in an appeal to the U. S. Court of Appeals for the Ninth Circuit.