Digital Data Sets Describing Water Use, Toxic Chemical Releases, Metropolitan Areas, and Population Density of the Conterminous United States

The data source for the water-use data is from the U.S. Geological Survey (USGS) (U.S. Geological Survey, 1990, 1998b; Lanfear, 1984). The toxic chemical release information is from the U.S. Environmental Protection Agency (1997, 1998), and the metropolitan area and population density data sets were derived from data provided by the U.S. Bureau of the Census (1995) and the Consortium for International Earth Science Information Network (1995).

Because most of the source materials do not cover Alaska and Hawaii, only the conterminous 48 states are included in these data sets. Compilation of the data sets was supported by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey. The objectives of the NAWQA Program are to: (1) describe current water-quality conditions for a large part of the Nation's freshwater streams, rivers, and aquifers, (2) describe how water quality is changing over time, and (3) improve the understanding of the primary natural and anthropogenic factors that affect water-quality conditions.