Surface electrical resistivity tomography and hydrogeological characterization to constrain groundwater flow modeling in an agricultural field site near Ferrara (Italy)

A portion of an unconfined alluvial aquifer located in the Padana Plain (Italy) was characterized following an integrated hydro-geophysical approach. Initially an electrical resistivity tomography (ERT) survey was employed to localize the boundaries of a modest paleo-channel body and to design the installation of a groundwater monitoring network. Multilevel slug-tests were performed to estimate the aquifer's saturated hydraulic conductivities. Determined permeability values together with electrical resistivity data were correlated. The correlation resulted in a site specific bi-logarithmic linear relationship. Based on this relationship, punctually determined hydraulic conductivities were spatially extended over the studied flow domain. Finally, continuously measured piezometric heads were used to calibrate a 3D flow model. Sensitivity analysis was performed to confirm the reliability of the reconstructed permeability field, as well as, to assess the minimum number of direct measurements needed to safely characterize the selected aquifer portion. The integration of the ERT survey results with the classical hydrogeological tests can be conveniently applied to constrain the permeability field during flow model calibration. Although the applicability of the determined relationship is site specific, the followed procedure is useful especially when there is a need to optimize the available resources and in case of small-scale pilot studies.