DELINEATION OF 3D SALTWATER PLUMES IN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER USING GEOSTATISTICAL ANALYSIS OF BOREHOLE AND AIRBORNE ELECTROMAGNETIC DATA

Salinization resulting from groundwater pumping for agricultural purposes has long been a concern in the northeastern Louisiana region, affecting the Mississippi River Valley alluvial aquifer (MRVA). The presence of saline water in wells has adverse effects on crop productivity, drinking water quality, and overall economic prosperity. The source of the saltwater in the MRVA is thought to be from either the underlying marine clay (Vicksburg-Jackson confining unit) or the much deeper Mississippi Interior Salt basin. However, the extent of saltwater plumes remains uncertain, impeding effective groundwater management. To address this issue, this study employs a geostatistical approach that integrates borehole data and USGS airborne electromagnetic (AEM) resistivity data. A large number of well logs were analyzed using indicator kriging to delineate MRVA sand facies. Additionally, a 3D resistivity model was developed using AEM frequency-domain data from 2019 and AEM time-domain data from 2020. To fuse the two resistivity datasets with different vertical resolutions, a cokriging method was employed, enabling a more comprehensive understanding of the resistivity architecture. The lithologic model and resistivity data were then used together to identify areas and depths of saline water, characterized by low resistivity values within the sand facies. Moreover, a power function was established to correlate observed chloride concentrations with AEM resistivity values. This relationship facilitated the delineation of 3D saltwater plumes in the MRVA. The results of this study provide valuable insights for stakeholders and future saltwater intrusion modeling, offering unprecedented information about the extent of chloride concentration within the aquifer.