Application of electrical resistivity tomography for imaging seawater intrusion in a coastal aquifer

Following previous geoelectrical researches initiated in 2009 for the delineation and characterization of seawater intrusion in a freshwater aquifer of Sarmatian (late Middle Miocene) age, a subsurface imaging survey via 2-D electrical resistivity tomography (ERT) was conducted in 2019 on the outskirts of Vama Veche resort-Romanian Black Sea southern coast. The survey was organized in the framework of a field camp sponsored by the Foundation of the Society of Exploration Geophysicists (SEG)-Tulsa, OK, USA, with participation of teams from the University of Bucharest-Department of Geophysics and the Geological Institute of Romania. A number of eight ERT profiles with N-S, W-E, NNE-SSW, and WNW-ESE orientation and 155-315 m length were imaged with a SuperSting R8/IP instrument (Advanced Geosciences Inc.), using deployments of 32-64 electrodes at 5 m spacing, in Wenner, Schlumberger, and dipole-dipole array configurations. The processing and interpretation of high-resolution ERT data indicated that the seawater intrusion, evidenced as very low resistivity (5-10 ohm m) anomalous zones starting at approximately 45-49 m depth, has advanced at least 500 m inland. The survey results also allowed the identification of a system of fractures or faults with an approximate NW-SE/WNW-ESE and, possibly, N-S orientation, that might have provided potential pathways for saline water intrusion.