National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 2001-2012

These data were released prior to the October 1, 2016 effective date for the USGS’s policy dictating the review, approval, and release of scientific data as referenced in USGS Survey Manual Chapter 502.8 Fundamental Science Practices: Review and Approval of Scientific Data for Release. 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").