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

Published by U.S. Geological Survey | Department of the Interior | Metadata Last Checked: February 10, 2026 | Last Modified: 2020-11-17T00:00:00Z
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 studied during the first decade of the NAWQA Program, from 1991-2001 ("cycle 1").

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