Geohydrology and susceptibility of major aquifers to surface contamination in Alabama; area 12

Abstract

The U.S. Geological Survey, in cooperation with the Alabama Department of Environmental Management, is conducting a series of geohydrologic studies to delineate the major aquifers and their susceptibility to contamination in Alabama. This report delineates and describes the geohydrology and susceptibility of the major aquifers to contamination in Area 12 which includes Coffee, Dale, Henry, Houston, and Geneva Counties. The major aquifers in Area 12 are the Upper Floridan aquifer which consists mainly of the Ocala Limestone; the Lisbon aquifer which consists of sand beds in the Lisbon, Tallahatta, and Hatchetigbee Formations; the Nanafalia-Clayton aquifer which consists of sand beds in the Nanaf alia Formation and sand and limestone beds in the Clayton Formation; and the Providence-Ripley aquifer which consists of sand beds in the Providence Sand and the Ripley Formation. Water in the Upper Floridan aquifer generally is unconfined; water in the other major aquifers is confined. The Nanafalia-Clayton aquifer is the most widely-used aquifer for public water supplies in Area 12. The ProvidenceRipley aquifer is used in northern and central parts of the study area, and the Upper Floridan and Lisbon aquifers are used in the southern part. Maximum withdrawals of ground water for public water supplies are estimated to be about 42 million gallons per day. Maximum withdrawals for irrigation are estimated to be 15 to 20 million gallons per day, and withdrawals for self-supplied industrial and domestic uses are estimated to be 3 and 2.5 million gallons per day, respectively. Long-term withdrawals of water from the Nanafalia-Clayton aquifer have resulted in significant declines in the potentiometric surface in the vicinities of Dothan, Fort Rucker, and Enterprise. The potentiometric surface has declined more than 100 feet at Dothan and 50 to 60 feet at Fort Rucker and Enterprise. The potentiometric maps for the Upper Floridan, Lisbon, and Providence-Ripley aquifers do not show significant declines in the potentiometric surfaces of these aquifers. Recharge areas for all the major aquifers are susceptible to contamination. However, because the recharge areas for the Providence-Ripley, NanafaliaClayton, and Lisbon aquifers are remote from their areas of use in Area 12, the probability of contamination is low. The recharge area for the Upper Floridan aquifer generally coincides with its area of use in the study area and consists of a relatively-flat sandy landscape that is extensively used for farming. Because of the highly-permeable nature of the recharge area and the use of insecticides and herbicides in the farming operations, the Upper Floridan aquifer in Area 12 is highly susceptible to contamination.