DELINEATING SALINITY IN LOUISIANA’S COASTAL AQUIFERS THROUGH THE INTEGRATION OF AIRBORNE GEOPHYSICAL AND BOREHOLE DATA

Groundwater is abundant in coastal Louisiana, making it a valuable resource for public supply, industry, and agriculture. The main coastal aquifers for groundwater consumption are the Mississippi River alluvial aquifer (MRAA) and the Chicot aquifer. The majority of groundwater withdrawals are for rice irrigation and aquaculture. Louisiana’s coastal aquifers are vulnerable to the threats posed by salinization and sea level rise. The sources of saltwater includes salt domes and the Gulf of Mexico (GOM). Saltwater can migrate vertically from deep formations into the aquifers or laterally from the GOM. Rising sea levels due to climate change will exacerbate the saltwater intrusion issue. However, to date, detailed three-dimensional (3D) salinity extents in the MRAA and the Chicot aquifer are lacking. This study integrates borehole data and recent airborne electromagnetic (AEM) data to map salinity in these aquifers. Borehole lithologic information was used to develop a 3D high-resolution hydrostratigraphic model. Borehole chloride data and AEM resistivity data were used to establish the resistivity-to-chloride concentration (R2C) relationship. Then, a geostatistical method was employed to develop 3D AEM resistivity architectures for the MRAA and the Chicot aquifer. Finally, the R2C relationship was used to delineate 3D chloride plumes in the MRAA and the Chicot aquifer. The results show extensive saltwater presence near the base of the Chicot aquifer, with saltwater upconing likely due to groundwater withdrawals. Additionally, a distinct tongue of saltwater extending northward from the GOM within the MRAA is delineated. The results also indicate higher salinity near the coasts, signifying seawater intrusion from the GOM. These findings provide valuable information for future groundwater management in Louisiana coastal aquifers to address sea level rise and climate change.