Respondents predecessors operated a coal gasification plant, which produced coal tar as a by-product, along a creek in Pennsylvania. Shortly after acquiring easements in the property along the creek, and while excavating to control flooding, the State struck a large deposit of coal tar which began to seep into the creek. Finding the tar to be a hazardous substance, the Environmental Protection Agency declared the site the Nations first Superfund site, and the State and the Federal Government together cleaned up the area. The Government reimbursed the State for cleanup costs and sued respondent to recoup those costs under 104 and 106 of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), 42 U.S.C. 9604 and 9606, claiming that respondent was liable because it and its predecessors had deposited the tar in the ground. Respondent filed a third-party complaint against the State, asserting, inter alia, that it was liable as an "owner and operator" of the site under 107(a) of CERCLA. The District Court dismis