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Groundwater quality and age to address water availability in the Mississippi River Valley Alluvial Aquifer
Proceedings of the 2020 Mississippi Water Resources Conference

Year: 2020 Authors: Killian C., Bussell A., Knierim K.J., Wacaster S., Gratzer M.

Existing and newly collected water quality data has been used to better characterize sources of water and improve the hydrogeology of the Mississippi River Valley alluvial (MRVA) aquifer, located within the Mississippi Embayment (MISE). Groundwater with high concentrations of metals, including iron and manganese, and areas of high salinity limit groundwater availability for irrigation, public supply, and domestic use. Water-availability issues within the MRVA aquifer have generated the need to improve water-budget estimates of existing regional groundwater-flow and three-dimensional machine-learning models. Groundwater age tracers, including tritium, carbon-14 (14C), sulfur hexafluoride (SF6), and noble gasses, were collected as part of the United States Geological Survey (USGS) Mississippi Alluvial Plain (MAP) regional water availability study help characterize sources of water to the MRVA aquifer. Sources of water to the MRVA aquifer include surficial recharge and upwelling from saline water from deeper hydrogeologic units. To map surficial hydrogeologic units of the MISE, the USGS is conducting a regional Airborne Electromagnetic (AEM) survey to detect changes in resistivity of subsurface units; however, the spatial and vertical distribution of groundwater specific conductance must be characterized to accurately interpret changes in resistivity. Accurate characterization of hydrogeologic units, especially where MISE units subcrop beneath the MRVA, will help identify drivers of groundwater quality and recharge of the MRVA aquifer. The results from this effort will help interpret data from the AEM survey, support three-dimensional machine-learning models of specific conductance and recharge-rate estimates as a part of the water budget for the MAP, and help to characterize areas where potential upwelling from deeper saline units may impact the availability of fresh water in shallower aquifers.

2017 MWRRI Annual Report
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