Integrating ERT and SP techniques for characterizing aquifers and surface-groundwater interactions

Authors: MAMUD, LAL - University Of Mississippi; HOLT, ROBERT - University Of Mississippi; HICKEY, CRAIG - University Of Mississippi; O'Reilly, Andrew - Andy; WODAJO, LETI - University Of Mississippi; RAD, PARSA - University Of Mississippi; SAMAD, ABDUS - University Of Mississippi

Submitted to: Groundwater
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2024
Publication Date: 10/24/2024
Citation: Mamud, L., Holt, R.M., Hickey, C.J., O'Reilly, A.M., Wodajo, L.T., Rad, P.B., Samad, A. 2024. Integrating ERT and SP techniques for characterizing aquifers and surface-groundwater interactions. Groundwater. https://doi.org/10.1111/gwat.13444.
DOI: https://doi.org/10.1111/gwat.13444

Interpretive Summary: Alluvial aquifers are composed of sediments deposited in a highly variable pattern by the meandering of a river in the geologic past. These sediments typically consist of coarse-grained very permeable sediments (sand and gravel) mixed with fine-grained less permeable sediments (silt and clay), which cause water to flow between the aquifer and the present-day river in ways that are difficult to predict. These characteristics are potentially impacting the effectiveness of a managed aquifer recharge pilot project being conducted by the USDA Agricultural Research Service at Shellmound, MS, to support sustainable agriculture. Two geophysical methods were applied that remotely sense subsurface characteristics from the ground surface: electrical resistivity tomography (ERT) for delineating variations in sediment grain size, and self-potential (SP) for monitoring groundwater levels and flow directions. These two methods were integrated to provide high resolution data to map the pattern of coarse- and fine-grained sediments composing the Mississippi River Valley Alluvial (MRVA) aquifer and monitor groundwater movement near a pumping well adjacent to the Tallahatchie River. The integrated analysis of both ERT and SP data showed that the river likely interacted with groundwater after 1 hour of pumping. The SP data showed greater drawdowns in groundwater levels in the MRVA aquifer on the northern side of the pumping well than the southern side likely due to variations in sediment grain size identified by ERT, whereas lesser drawdowns to the east indicated greater flow of water toward the well from the river side. The successful integration of ERT with the SP method provides scientists and water managers with a tool for monitoring groundwater flow and investigating interactions between rivers and aquifers without costly installation of dense monitoring well networks.

Technical Abstract: This study enhances the understanding of riverbank filtration and improves management of the Mississippi River valley alluvial (MRVA) aquifer during a managed aquifer recharge (MAR) pilot project at Shellmound, MS. Using high-resolution electrical resistivity tomography (ERT) and self-potential (SP) geophysical methods, we characterized the heterogeneous MRVA aquifer and monitored groundwater flow near a pumping well. ERT was used to provide detailed spatial characterization, filling gaps left by airborne electromagnetic (AEM) data and soil boring logs, while SP techniques were used to monitor groundwater flow, predict drawdown trends, and investigate surface-groundwater interactions. Results showed that SP signals were influenced by groundwater flow, river infiltration, and water mixing due to pumping disturbance of natural geochemical stratification, with significant river interaction observed after 1 h of pumping. The integration of ERT and SP methods revealed lithologic heterogeneity, explaining greater drawdowns on the northern side of the well and increased flow from the riverside. This comprehensive approach offers valuable insights into aquifer management and sustainability.