Louisiana ground-water map no. 13 [electronic resource] : hydrogeologic and potentiometric surface, October 1996, of the Sparta Aquifer in northern Louisiana / by Jeffrey A. Brantly, Ronald C. Seanor, and Kaycee L. McCoy ; U.S. Department of the Interior, U.S. Geological Survey ; prepared in cooperation with the Louisiana Department of Transportation and Development, Public Works and Water Resources Division, Water Resources Section