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AN OVERVIEW OF GEOELECTRICAL SURVEYS FOR THE ASSESSMENT OF SEAWATER INTRUSION FROM THE ROMANIAN BLACK SEA COASTAL AREA
Abstract
A major risk factor for freshwater coastal aquifers is represented by seawater intrusion, consisting of the movement of marine saltwater into these aquifers. This occurs due to sea level changes, tidal fluctuations, changes in evaporation and recharge rates, fractures in coastal rock formations, or excessive freshwater pumping. The negative effects of this salinization phenomenon are a reduction in the available freshwater storage volume, the contamination, and the abandonment of production wells. In Romania, such intrusion has occurred in the southern part of Black Sea's coastline, in Costinesti and Vama Veche resorts, affecting the main aquifers hosted in late Middle Miocene limestones. In Costinesti area, Vertical Electrical Sounding (VES) surveys were carried out repeatedly between 1991 and 2010, along a 900 m length WNW?ESE profile on the lineament of several water exploitation wells and pumping stations. These surveys identified and monitored a significant minimum resistivity anomaly associated with a seawater intrusion, at about 2000 m distance from the coastline, generated by the overexploitation of drinking water. The reduction of freshwater exploitation led to diminishing contamination and gradual disappearance of the associated resistivity anomaly. In Vama Veche area the geoelectrical researches were initiated in 2009, with 23 VES surveys performed on two parallel profiles of about 800 m length each and with WSW?ENE orientation. This investigation revealed on the southern profile a minimum resistivity anomaly associated with a seawater intrusion at 45 m average depth, advancing at least 150?200 m inland. The researches were restarted in 2019, in the framework of a Field Camp supported by the Society of Exploration Geophysicists. A number of 8 profiles with N?S, W?E, NNE?SSW and WNW?ESE orientation and a total length of 1800 m were imaged via 2D Electrical Resistivity Tomography (ERT). These ERT surveys indicated that the seawater intrusion is more extended than initially considered, reaching at least 500 m distance from the coastline. They also allowed the identification of potential intrusion pathways, represented by a system of fractures or faults with an approximate NW?SE/WNW?ESE and, possibly, N?S orientation.
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