Large Scale Electrical Resistivity Tomography Survey Correlated to Hydrogeological Data for Mapping Groundwater Salinization: A Case Study from a Multilayered Coastal Aquifer in Rhodope, Northeastern Greece

Abstract

A large scale two dimensional electrical resistivity survey was carried out to investigate groundwater salinization phenomena of a multilayered coastal aquifer in south Rhodope area, northeastern Greece. The electrical resistivity tomography (ERT) profiles, calibrated with lithological, physicochemical and geophysical log data, were used to demarcate the geometry of the aquifer system and characterize the extent of the interface between saline and freshwater in a coastal groundwater system, which has been subject to overexploitation for the last 35 years. In total, 12 deep high resolution ERT profile lines, covering a distance of approximately 15 km were carried out at key locations across the downgraded part of the aquifer system. The resistivity sections were calibrated using a reference dataset of 45 information wells incorporating 28 lithological logs, 31 groundwater quality samples from a variety of screen placements and five gamma ray logs. Results revealed the presence of four major resistivity zones ranging in values between 0.1 and 150 Ωm at various depths and locations. A very low resistivity zone (0.1-5 Ωm) correlated with saline water saturated layers, a medium resistivity zone (5-15 Ωm) attributed to clays and silts, and two high resistivity zones generally representing freshwater saturated sediments of coarse grain size (15-40 Ωm) or alterations of thin marl and fine sand layers (40-150 Ωm). It is demonstrated that extensive use of high resolution deep geoelectrical sections, calibrated with a large number of hydrogeological data can successfully delineate aquifer geometry dimensions, identify hydraulic boundaries and clarify ambiguous field measurements, thus allowing the development of a thorough hydrogeological conceptual model.

Detection of Ground Water Availability at Buhias Island, Sitaro Regency

“…So it can be said that in the fourth trajectory contained a layer of salt water because the area is mostly swamp. In the area is in line with the research of Galazoulas et al (2015) that uses a resistivity zone showed the phenomenon of groundwater from coastal aquifers successfully illustrated by groundwater aquifer that is four major resistivity zones ranging in values between 0.1 and 150 Ωm at various depths and locations. A very low resistivity zone (0.1-5 Ωm) correlated with saline water saturated layers, a medium resistivity zone (5-15 Ωm) attributed to clays and silts, and two high resistivity zones generally representing freshwater saturated sediments of coarse grain size (15-40 Ωm) or alterations of thin marl and fine sand layers (40-150 Ωm).…”

High-Resolution Electrical Resistivity Tomography (ERT) to Characterize the Spatial Extension of Freshwater Lenses in a Salinized Coastal Aquifer

“…The electrical resistivity tomography (ERT) method was successfully applied to the spatial characterization of saltwater intrusion in coastal areas [12,[17][18][19][20], but has not yet been used to map thin freshwater lenses. ERT is especially useful wherever a network of boreholes, piezometers, and direct sampling of groundwater are available [21,22]. The point measurements are useful to calibrate the ERT method that is then used to create a series of two-dimensional images of freshwater-saltwater distribution in the aquifer [19].…”

Geophysical methods in protected environments. Electrical resistivity tomography

“…La resistividad de las rocas del subsuelo está relacionada con diversos parámetros: los minerales contenidos, la porosidad, el fluido que rellena los poros, el grado de saturación de agua de la roca, la salinidad del fluido, la temperatura, etc. Ejemplos de estudios previos en los que se aplicó este método en estudios hidrogeológicos se pueden encontrar en Ball et al (2010), Ratnakumari et al (2012), Galazoulas et al (2015); en casos de vertederos y detección de cavidades en Meads et al (2003), Chamberst et al (2006), Martínez-Pagan et al (2013) y Martínez-Moreno et al (2013; en zonas kársticas en Zhou et al (2002). Además, el casi inexistente impacto que esta técnica produce sobre el terreno hace de ella una opción muy recomendable para investigar el subsuelo de zonas protegidas con fines científicos o medioambientales.…”