The author is a partner in the law firm of Campbell, George & Strong (CG&S) LLP, http://www.cgs-law.com. He has a broad background in complex federal civil and environmental litigation. Prior to becoming a partner at CG&S, the author was a Senior Attorney with the U.S. Department of Justice, Environment and Natural Resources Division, where he headed the San Francisco field office for the division's Environmental Enforcement Section. In this position, he served as lead counsel for the federal government on major environmental enforcement suits under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), the Clean Water Act, and the Clean Air Act.Cross-boundary pollution is a long-recognized reality for the United States and its neighbors, one that goes in both directions. Water pollution from Tijuana flows into the United States, fouling beaches at San Diego's Mission Bay. Air pollution from coal-fired power plants in the United States drifts into Canada, causing acid rain. These examples hardly begin to exhaust the possibilities. While there are complexities associated with attempting to do so, there is little question that the United States--or whatever affected country--could try to address these transboundary contamination issues. There is, however, considerable doubt about the extent to which the U.S. Congress has authorized the U.S. Environmental Protection Agency (EPA) to do so under existing environmental law.