Ground-water resources of the Arkansas River basin in Arkansas

The Arkansas River basin in Arkansas lies almost entirely within the Interior Highlands physiographic division. The Interior Highlands consist of hilly to mountainous terrain underlain by sandstone, shale, limestone, and dolomite. That part of the basin southeast of Little Rock lies within the Gulf Coastal Plain and is characterized by flat to hilly topography. Significant water-yielding units within the Arkansas River basin include subsurface Paleozoic units such as the Eminence and Potosi Dolomites, the Gasconade Dolomite, and the Van Buren Formations, and Roubidoux Formation as well as outcrops of Paleozoic rocks, the Sparta Sand, and Quaternary deposits. The quality of groundwater withdrawn from the various aquifers in the study area is generally suitable for most uses, although commonly very hard and highly mineralized. Only the Sparta Sand yields a soft, less mineralized water. Yields from the different water-bearing units are highly variable. Several of the subsurface Paleozoic rocks rarely yield more than 10 gal/min. In the Coastal Plain, the Sparta Sand and the Quaternary deposits yield as much as 2,000 and 2,500 gal/min, respectively. Several studies have indicated substantial bacterial contamination of both wells and springs in this part of the study area. Also, nitrate concentrations that exceed U.S. Environmental Protection Agency primary drinking water standards occur in some areas. (USGS)