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 Ω 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.