1 Volume data based on published reports by the Congressional Research Service, the New York City Department of Sanitation, and other independent studies; on conversations with state officials; and on a private waste industry survey conducted by NSWMA. Most of the volume data cover calendar year 1989, but a few volumes reflect periods in 1990. The volume data and the export transactions between states are dynamic and subject to change. For example, New Jersey officials have not only revised downward their own export data for 1989, but also estimated further reductions in 1990 of more than one million tons. Also, Delaware is currently exporting some waste to Pennsylvania because of temporary difficulties at a waste-to-energy plant, and Montana now exports small volumes of waste from Yellowstone National Park to Idaho.