Numerical Study of Groundwater Transfer and Injection Pilot Project In The Mississippi River Valley Alluvial Aquifer Using A Groundwater Model With Airborne Resistivity Data

Declines in groundwater levels resulting from agricultural irrigation have been observed and reported for the past decades in the Mississippi River Valley alluvial aquifer (MRVAA), showing that the current management of groundwater resources is not sustainable. To mitigate this problem, a Groundwater Transfer and Injection Pilot (GTIP) project was initiated by the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) at Shellmound, Mississippi, which consists of one extraction well, two injection wells and 17 observation wells. Field experiments and measurements are essential to test the feasibility of the project, while numerical modeling is important for the evaluation of potential designs. Therefore, a numerical groundwater model was developed for this pilot project. The modeling domain was approximately 10 km by 10 km in the horizontal plane, and the thickness was 52.0 m. The modeling results are significantly affected by the spatial distribution of the aquifer hydraulic conductivity. However, it is generally impossible to measure the hydraulic conductivity distribution directly. Considering the correlation between the sediment resistivity and the hydraulic conductivity, airborne resistivity data measured by the U.S. Geological Survey were incorporated into the groundwater model. An empirical formula was adopted to translate the resistivity data into the hydraulic conductivity. The parameters in the empirical formula were determined by calibrating the numerical model with the measured groundwater levels from April 14 to April 18 in 2021. The spatial distribution of the parameters in the formula were considered by introducing pilot points. Different numbers of pilot points were tested to find the best-fit result. The calibrated model was then verified with the measured data from April 19 to May 22 in 2021. Good agreement between the simulation results and the measured data indicates the potential of using airborne resistivity data to guide development of a groundwater model for the GTIP project, which can be used to facilitate decision-making on the feasibility of this aquifer recharge technology.