ENHANCING HYDROGEOLOGIC STUDIES IN THE MISSISSIPPI ALLUVIAL PLAIN THROUGH INTEGRATION OF AIRBORNE GEOPHYSICAL DATA AND DERIVED PRODUCTS

Groundwater within the Mississippi Alluvial Plain (MAP) aquifer system is a critical resource used heavily by the agricultural industry and municipalities. Detailed knowledge of the hydrogeologic framework, aquifer properties, and water quality is vital for understanding the current and future state of water resources in the MAP region. As part of the U.S. Geological Survey MAP Regional Water-Availability Study, approximately 80,000 line-km of airborne geophysical (electrical resistivity, radiometric, and magnetic) data were collected from 2018–2022 over the MAP region to provide system-scale subsurface mapping of the Mississippi River Valley Alluvial aquifer (MRVA) and its context within the larger hydrogeologic system. Using airborne electromagnetic data, we produced a three-dimensional (3D) regional model of electrical resistivity aligned with the 1x1 km National Hydrogeologic Grid reaching maximum depths of 300 m, as well as a higher resolution (100x100 m) inset model for Shellmound, MS. The resistivity models were used to derive hydrogeologic products mapping the degree of confinement or connectivity in surface material, shallow streambed properties, an updated basal surface of the MRVA, and a measure of degree of hydrologic connection between the MRVA and deeper aquifers. These products have been integrated into several aspects of groundwater investigations across multiple scales and have resulted in enhanced outcomes and new insights into the aquifer system. The 3D models of electrical resistivity have been used to inform hydrogeologic parameterization (e.g., hydraulic conductivity and storage coefficients) and layer representation in numerical groundwater flow modeling, resulting in improved model performance and estimates of transmissivity. Resistivity data, soil radiochemistry, and the degree of surface confinement are being used in machine learning models predicting both water quality and groundwater levels. The geophysical data are proving influential in flow modeling and are improving 3D predictions of groundwater salinity as well as manganese and arsenic concentrations. Results from the MAP region demonstrate how incorporation of system-scale airborne geophysical data to inform hydrogeologic properties and processes can enhance studies of groundwater resources.