40 CFR 761.99: Other transboundary shipments.

For purposes of this subpart, the following transboundary shipments are not considered exports or imports:

(a) PCB waste generated in the United States, transported outside the Customs Territory of the United States (including any residuals resulting from cleanup of spills of such wastes in transit) through another country or its territorial waters, or through international waters, and returned to the United States for disposal.

(b) PCB waste in transit, including any residuals resulting from cleanup of spills during transit, through the United States (e.g., from Mexico to Canada, from Canada to Mexico).

(c) PCB waste transported from any State to any other State for disposal, regardless of whether the waste enters or leaves the customs territory of the United States, provided that the PCB waste or the PCBs from which the waste was derived were present in the United States on January 1, 1979, and have remained within the United States since that date.