WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2004TN13B
Title: An Investigation of Surface-Ground Water Connections at Nonconnah Creek: A Source of Recharge and Potential Contamination for the Memphis Aquifer in Shelby County Tennessee
Project Type: Research
Focus Categories: Non Point Pollution, Groundwater, Surface Water
Keywords: groundwater hydrology, groundwater movement, age dating, groundwater recharge, urban hydrology, groundwater quality
Start Date: 03/01/2004
End Date: 08/31/2005
Federal Funds: $25,381
Non-Federal Matching Funds: $55,170
Congressional District: TN9
University of Memphis
The proposed project investigates the potential of surface water from an impaired watershed (Nonconnah Creek) to infiltrate into a shallow aquifer system that recharges an aquifer (Memphis aquifer) used for a municipal water supply. This project is an expansion of a long-term study to investigate the potential for modern water to enter the Memphis aquifer in the Sheahan well field, Memphis, Tennessee. Published results of our current research indicate that water pumped from shallow production wells in the Memphis aquifer contains as much as 30% of a chemically distinct modern water (15 to 20 year residence time) that is entering the upper part of the Memphis aquifer near the Sheahan well field. The shallow aquifer overlying the upper Claiborne confining unit and Memphis aquifer is unsaturated near the Sheahan pumping station, but becomes progressively saturated toward Nonconnah Creek, 2.7 miles south of the pumping station. Previous investigators determined that Nonconnah Creek loses water to the shallow aquifer in the Memphis area, although no quantitative information is available. Most recently, lumped parameter tracer models have been coupled with inverse computational methods and geochemical data to determine fluxes of modern water to individual well and a location of leakage from the shallow aquifer in the center of the well field. Unpublished finite-difference flow modeling results and model calibration further suggest that various wells in the Sheahan well field receive water from the shallow aquifer, most likely from Nonconnah Creek. We propose to determine if Nonconnah Creek is the ultimate source of the modern water recharging the Memphis aquifer near the Sheahan well field. Considering that Nonconnah Creek receives urban and agricultural runoff and contains significant pollutant loadings and that the shallow aquifer beneath Nonconnah Creek contains agricultural pollution, it is important to assess shallow aquifer contributions to the urban water supply. The results of the project have the potential to influence ground-water exploitation strategies, watershed management, and source-water protection policies in the Memphis area and surrounding region.
The project is designed to determine the flux and quality of water from Nonconnah Creek to the shallow aquifer during a one-year period. The flux will be assessed by multiple techniques, in part because of uncertainties in applying any one strategy. New and existing monitoring wells will be used in the shallow aquifer near Nonconnah Creek to observe vertical and lateral gradients away from the stream channel. Stream discharge and head measurements will be made upstream and downstream of the monitoring wells to assess stream losses (or gains) directly. The ground-water head and stream discharge data will be used to further calibrate our ground-water flow model for the Sheahan well field. Major and minor solute chemistry of stream and ground water will be used to evaluate influx and mixing among various waters, and chemical processes in the aquifer. In addition, 3H/3He and chlorofluorocarbons will be used as tracers of surface water influx and to determine ground-water velocities away from the stream. A recently developed computer code for inverse modeling of tracer data will be used to assess stream contributions to several production wells and the quantity of recharge received. Comparison to previous results will indicate whether the Nonconnah Creek waters recharge all or part of the shallow Memphis aquifer production wells in the Sheahan well field and, if so, the travel times from the stream to the wells. Quantitative modeling information such as that proposed is needed to develop ground-water pumping strategies and source-water protection plans for the Memphis area. Similar aquifer interrelationships exist throughout the Mississippi Embayment and Gulf Coast regions and we expect that the results will have broad implications for regional water use and development.