National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 1991-2001

Release Date

2006-01-31

Publication Date

2023-09-15

Hitt, K.J. and Nakagaki, N., 2006, National Water-Quality Assessment (NAWQA) Study-Unit Investigations in the conterminous United States 1991-2001: U.S. Geological Survey data release, https://doi.org/10.5066/P9JL08QN.

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The National Water-Quality Assessment Program is a primary source for long-term, nationwide information on the quality of streams, ground water, and aquatic ecosystems (Gilliom and others, 2001). The goals of NAWQA are to assess the status and trends in the quality of the Nation's ground- and surface-water resources and to provide a sound understanding of the natural and human factors that affect the quality of these resources (Leahy and others, 1990). Study Units are defined by major river basins and aquifers across the Nation (Gilliom and others, 2001). This coverage contains the boundaries for the Study Units within the conterminous United States (excluding the High Plains Regional Ground Water-Study) that were defined during cycle 1 of NAWQA. During cycle 1 of NAWQA, 51 studies actually were undertaken (49 in the conterminous U.S. and one each in Alaska and Hawaii), and 8 were not scheduled. This coverage depicts 57 Study Units: 49 actually studied and 8 not scheduled. The coverage also includes the name, starting date, and NAWQA standard abbreviation of each Study Unit plus various codes to help display the data. The second cycle of NAWQA (2001-2012) will adjust its scope to 42 of these important river basins and aquifer systems to accommodate budget reductions. The second cycle of investigations began in 14 Study Units in 2001. Although the boundaries of most Study Units remain the same in cycle 2, the boundaries and codes for cycle 2 Study Units are maintained in a separate data set (NAWQACYC2). This data set is used primarily to display the location of NAWQA Study Units and for analysis of data at the national scale. It is not recommended for either local or regional analysis due to the small scale of most of the features.

• Model Data Management Function (MDMF)