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Mapping the Variability of Specific Conductance in Groundwater of the Mississippi River Valley Alluvial Aquifer
Proceedings of the 2019 Mississippi Water Resources Conference
Year: 2019 Authors: Killian C., Bussell A., Knierim K., Kingsbury J., Wacaster S., Kress W.H.
The Mississippi River Valley alluvial (MRVA) aquifer is the uppermost aquifer underlying the Mississippi Alluvial Plain (MAP) and spans portions of eight states within the Mississippi Embayment. The MRVA aquifer supplies most of the groundwater used for irrigation throughout the MAP. Water-quality conditions in parts of the aquifer may limit the availability of groundwater for irrigation, public supply, and domestic use. To better understand and map the water resources of the MAP, the U.S. Geological Survey (USGS) designed an Airborne Electromagnetic (AEM) survey to map resistivity of hydrologic units at the regional scale. Mapping resistivity changes of hydrologic units will help identify the primary drivers that influence groundwater quality in the MRVA aquifer. To accurately interpret the AEM survey data and the changes in resistivity, the spatial and vertical distribution of groundwater specific conductance throughout the aquifer needed to be delineated. This study compared newly collected and existing historical specific conductance and chloride data from over 1,500 existing wells and cooperatively funded water-quality monitoring sites screened in the MRVA aquifer to changes in geomorphology, recharge rates, and well depth. The results from this study will support threedimensional machine-learning models of specific conductance and recharge-rate estimates as a part of characterizing the water-budget components in the MAP. Results will also help to predict aquifer salinity across the region and help to characterize areas where possible upwelling from deeper saline units may impact the availability of fresh water in shallower aquifers.