ASSESSMENT OF MANAGED AQUIFER RECHARGE FEASIBILITY FOR A PILOT FACILITY UTILIZING RIVERBANK FILTRATION AND GROUNDWATER TRANSFER AND INJECTION TO SUPPORT SUSTAINABLE AGROECOSYSTEMS

Long-term depletion of the Mississippi River Valley alluvial aquifer (MRVAA) threatens sustainability of groundwater-irrigated agroecosystems in the intensively cultivated Lower Mississippi River basin. The U.S. Department of Agriculture Agricultural Research Service partnered with local stakeholders and U.S. Army Corps of Engineers to conduct the Groundwater Transfer and Injection Pilot (GTIP) project to test the feasibility of a managed aquifer recharge (MAR) system, which combines riverbank filtration with groundwater transfer and injection to increase groundwater levels in the Delta region of Mississippi. The system consists of one extraction well, a 1.8-mile pipeline, and two injection wells, with a design capacity of 1,500 gal/min. Operation began in 2021, and two injection tests were conducted for durations of 89 and 204 days, yielding total injected volumes of 550 and 575 ac-ft, respectively. Increases in groundwater levels up to 6.7 ft occurred at the injection site and decreases as much as 4.7 ft occurred at the extraction site. During both tests, differences in water chemistry between the river and extraction well indicate increased mineralization due to rock-water interactions and biogeochemical processes during riverbank filtration, whereas relatively small changes in water chemistry occurred in the MRVAA at the injection site. Findings of the GTIP project demonstrate technical feasibility of the MAR technology but also illustrate guidelines moving forward, including (1) assimilate ongoing data collection with design and operation of the extraction and injection wells; (2) maintain similar water chemistry between injected water and ambient groundwater; (3) coordinate operational schedule with river stage and riverbank filtration capacity; and (4) implement technology to reduce iron concentrations in backflush water below regulatory limits before discharging to a surface water body. Additional analysis, modeling, and potential design modifications, which will be needed to answer the broad question of feasibility for a large-scale implementation of MAR technology throughout the Delta, will also be discussed.