Methods and results in mapping of chloride and specific conductance and analysis of changes in chlorides in the Chicot aquifer system in southwest Louisiana

The Chicot aquifer system is an abundant and valuable source of water for agriculture and public supply water use in southwest Louisiana. Chloride concentrations exceed threshold criteria for use in public supply (Secondary Maximum Contaminant Level for drinking water of 250 mg/L) and also in agriculture in some portions of the Chicot aquifer system. There is a need for periodic mapping and analysis of change in chlorides across the Chicot aquifer system. This investigation constructed a general approach, which included evaluation of various geostatistical models, to map chloride concentrations across the aquifer in southwest Louisiana. The approach and model had to account for the origins of chlorides and the practical (i.e., non-ideal) characteristics of the data available. Possible sources of chloride in the include the upconing of deeper saltwater, anthropogenic activities, faulting, and salt domes. Data set characteristics included significant variation in frequencies, depths, and spatial distribution which were the result of data being collected by multiple agencies. Results of the study indicate that chloride concentrations and variability by depth and time are greatest in the southern parts of the Chicot aquifer system. Derivative results include refinement of a systematic approach to mapping chlorides utilizing a geostatistical approach, metrics for data sampling network design, and cooperative data collection. The methodological framework and its results achieved the project goal to assist in the utilization and management of the Chicot aquifer system as a resource in a robust manner from the local level to the regional level.