Using Vertical Electrical Soundings to characterize seawater intrusions in the southern area of Romanian Black Sea coastline

Abstract

Seawater intrusions are a major environmental hazard for coastal freshwater aquifers. They are generated mainly by the uncontrolled exploitation of freshwater in pumping stations, if the aquifers are in hydraulic connection with the sea. In Romania, such marine intrusions have occurred in the southern part of Black Sea’s coastline, in Costinești and Vama Veche resorts, contaminating the main aquifers hosted in Sarmatian (late Middle Miocene) limestones, at distances ranging from hundreds of meters to over 2 km inland. For the study of these salinization phenomena, Vertical Electrical Sounding (VES) surveys were performed in the affected areas. These surveys allowed the delineation and spatial–temporal monitoring of the intrusions and offered information related to faults that may have provided pathways for seawater migration toward the exploitation wells. The 1D interpretation of VES apparent resistivity data was performed via a set of novel software applications. The forward modeling component of the applications uses digital linear filtering and allows the simulation of theoretical VES responses for horizontally-layered geological media with virtually unlimited number of layers. The pseudo-inversion component of the applications is based on a random sampling of the parameters space of the geoelectrical models. The interpretation of VES surveys recorded in Vama Veche area by using the elaborated software indicates that the seawater intrusion occurs at more than 40 m depth. This agrees with a well flow test which produced saltwater at 40–60 m depth in that area.