Milner, L. Riley¹, Sean McLaughlin² 
(1) Louisiana Geological Survey, Baton Rouge, LA 
(2) Injection and Mining Division, Louisiana Department of Natural Resources, Baton Rouge, LA

ABSTRACT: Preliminary Geologic Characterization of the Chicot Aquifer in Southwest Louisiana - Acadia, Allen, Beauregard, Calcasieu, Evangeline, and Jerfferson Davis Parishes

Rapid urban growth and increased use of ground water for agriculture and industry has brought the issue of aquifer sustainability to the forefront in many areas of the country and throughout the world. A drought season in 1998 resulted in farmers finding salt water flowing in their fresh water wells in some coastal areas of Louisiana. The Louisiana Legislature subsequently formed a water commission and advisory group to address the water issues of the state. The Louisiana Geological Survey is conducting a reservoir characterization and modeling study of the Chicot Aquifer system . Oil, gas, and water well electric logs and drillers? logs were used to identify the different stratigraphic and hydrochemical facies of the Chicot Aquifer. The fresh water/salt water interface, or the beginning of the transition zone into more saline water, was shown by the significant reduction in resistivity displayed on the electric logs. An approximate position of the base of the fresh water was determined from the resistivity curve with 40 ohms as the cut-off. 
The Chicot Aquifer is Pleistocene in age, and is composed of fine sand and gravel interspersed with thin intermittent clay layers to very thick confining clay layers. A number of salt domes with associated radial faulting occur below the Chicot Aquifer, and show their presence in the overlying sediment up into the base of the Chicot Aquifer and their associated radial faulting. Deep-seated listric faults also occur beneath and into to the base of the Chicot Aquifer. Some of these listric faults have been found to propagate to the surface creating a possible conduit for salt water to migrate up into the fresh water zone within the Chicot Aquifer.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.