The Ozark Plateaus NAWQA is one of more the 50 study units that are part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. The Ozark Plateaus study unit is approximately 48,000 square miles in size and includes parts of northern Arkansas, southeastern Kansas, southern Missouri, and northeastern Oklahoma.
The Sparta aquifer is Union County's only source of municipal and industrial ground water. Since development began in the early 1920's ground-water levels have declined more than 390 feet in some areas. As a result, Union was among five southern Arkansas counties designated as the state's first "Critical Ground Water Area" in 1996.