MANAGED AQUIFER RECHARGE UTILIZING RIVERBANK FILTRATION AND GROUNDWATER TRANSFER AND INJECTION FOR SUSTAINABLE GROUNDWATER IN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER (Invited Presentation)

In the intensively cultivated Delta region of Mississippi, long-term declines in groundwater levels in the Mississippi River Valley alluvial aquifer (MRVAA) indicate that groundwater-use practices are unsustainable. A pilot facility using managed aquifer recharge is being tested to assess the potential for this technology to mitigate groundwater depletion, supporting irrigated agriculture as well as sustaining natural ecosystems. In partnership with local stakeholders and the U.S. Army Corps of Engineers, the U.S. Department of Agriculture Agricultural Research Service is conducting the Groundwater Transfer and Injection Pilot (GTIP) project near Greenwood, Mississippi. The system consists of one extraction well, a 1.8-mile pipeline, and two injection wells, with a design capacity of 1,500 gpm. Groundwater is filtered by passing through sands adjacent to the Tallahatchie River and subsequently is extracted, transferred, and then injected into a depleted section the MRVAA. Operation began in April 2021, and an initial 3-month test injecting a total of 550 ac-ft of water has been completed. Data collection at 17 observation wells and the extraction and injection wells includes continuous groundwater level and temperature and monthly water samples for analysis of major ions, metals, and nutrients. A second test period commenced February 2022 and will continue up to 6 months. During the initial test, changes in water chemistry during riverbank filtration indicate increased mineralization attributable to rock-water interactions and biogeochemical processes. Relatively small changes in water chemistry were observed near the injection wells, while a groundwater mound formed approximately 1.5 miles in diameter and 1–7 ft in height. Local scale numerical modeling is being conducted to quantify hydrological processes governing riverbank filtration and injection processes. The simulation domain is 6 by 6 miles in the horizontal plane, and the thickness of the simulated aquifer is 164 ft. The numerical model has been calibrated and verified showing good agreement with measured groundwater levels from April to May in 2021. Knowledge acquired during the GTIP project will be combined with future regional-scale numerical modeling to estimate impacts and feasibility of a potential full-scale implementation.