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Overview and status of the Groundwater Transfer and Injection Pilot Project at Shellmound, Mississippi
Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Wren D.G., O'Reilly A.M., Locke M.A., Bolton W.J., Mirecki J.E.

In the Mississippi Delta region (Delta), long-term declines in groundwater levels in the Mississippi River Valley alluvial aquifer (MRVAA) indicate that groundwater-use practices are unsustainable. Managed aquifer recharge (MAR) has potential for reducing groundwater depletion in the Delta. In partnership with local stakeholders and the U.S. Army Corps of Engineers, the USDA Agricultural Research Service is conducting the Groundwater Transfer and Injection Pilot (GTIP) project, which combines riverbank filtration and aquifer storage to capture water from the Tallahatchie River for direct injection into the MRVAA. The system consists of one extraction well near the river, a 1.8-mile transfer pipeline, and two injection wells. The system has a design capacity of 1,500 gpm with 750 gpm sent to each injection well. Monitoring includes continuous groundwater level and temperature in 17 monitor wells (14 MRVAA, 3 Sparta aquifer); semimonthly field parameters (temperature, specific conductance, pH, dissolved oxygen) at six MRVAA monitor wells; monthly water samples for analysis of major ions, metals (Fe, Mn, As), and nutrients (N, P, C) from all monitor wells, extraction and injection wells, Tallahatchie River, and Lake Henry (lake adjacent to the injection wells); and annual water samples for a large suite of trace metals and pesticides from 4 monitor wells and both injection wells. Hydraulic connection between the river and MRVAA is suggested by variations in groundwater level, temperature, and specific conductance. Ambient groundwater prior to operation was less mineralized at the extraction site than the injection site, and water levels in monitor wells near the river showed responses to river stage that were not evident in more distant wells near the injection site. Operation began April 2021, and an 89-day test injecting a total of 550 ac-ft of water has been completed. This resulted in a groundwater mound of 6.9 ft near the injection wells and a drawdown of 4.6 ft near the extraction well, prior to commencement of regional drawdowns in June caused by irrigation pumping. Clogging of the injection wells necessitated periodic backflushing followed by treatment with a dilute oxalic acid solution, which resulted in returning injection well specific capacities to within 85% of initial values. Current plans are to resume operation and data collection for an additional 3 to 6 months. Knowledge acquired during the GTIP project will be used to assess feasibility of a full-scale implementation of MAR technology in the Delta.

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