Groundwater Exploration Tools and Strategies in Southeastern Alabama

            Coastal plain sediments in southeastern Alabama, ranging in age from Cretaceous to Tertiary, contain one of the region's most valuable natural resources – groundwater - yet delineation of the aquifers commonly is risky due to lack of data or inadequate analyses to predict sand or limestone thicknesses. Geophysical well logs, acquired in a portion of the wells drilled in the region, are valuable tools that can be used to map structure and to delineate sand and limestone thicknesses and trends in order to reduce the risk of finding adequate aquifer thicknesses for development of public water supplies.  

In this study, encompassing all or portions of 10 counties in southeastern Alabama and conducted for the Choctawhatchee-Pea-Yellow Rivers Water Management Authority, geophysical logs from 119 wells were analyzed.  Net sand or limestone determinations were made primarily by using natural gamma logs with the aid of resistivity and spontaneous potential logs.  Sand and/or limestone content greater than 75 percent was estimated from the logs and a summation of net feet of sand (or limestone) for each aquifer in each well was determined.  The data were then contoured and displayed as net feet of sand (or limestone) maps.  Maps were constructed for the Cretaceous Gordo, Eutaw, and Ripley aquifers and for the Tertiary Clayton, Salt Mountain, Nanafalia, and Tallahatta aquifers.  The use of depositional models aided in mapping the sand and limestone trends. 

The results of this study have already seen application in assisting municipalities and water authorities in their well site selection processes and planning.  Coupled with potentiometric maps, water quality data, and drawdown modeling, the on-going use and refinement of the aquifer thickness data and interpretations can be utilized to prudently develop the groundwater resources of the region and reduce risks associated with drilling.