The Colville Confederated Tribes say they may file a lawsuit to force the [U.S.] Environmental Protection Agency to declare Lake Roosevelt a Superfund site, or accept a voluntary cleanup by the owners of a Canadian smelter...The records show that Cominco [Teck Cominco Ltd.] has dumped as much as 9.8 million tons of black wastes called "slag" and tons of mercury, sulfuric acid and other chemicals into the river for more than 60 years.