This is a coverage of the boundaries and codes used for the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program Study-Unit investigations in the conterminous United States, excluding the High Plains Regional Ground-Water Study. The data set represents the areas to be studied during the second cycle of the NAWQA Program, from 2001-2012 ("cycle 2").
Additional publication details
USGS Unnumbered Series
National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 2001-2012