Application of time domain induced polarization technique to study perched groundwater at the northwestern coast of Egypt: A case study of Fuka basin

Abstract

Perched groundwater resources, essential for drinking, tourism, and irrigation, have not been extensively studied. These resources are finite, vary in salinity, and are threatened by overexploitation, contamination, and rising sea levels due to climate change. A survey using Two-Dimensional Electrical Resistivity Tomography (2DERT) and Time Domain Induced Polarization (2DTDIP) techniques was conducted in the Fuka basin to map the shallow perched aquifer, determine stratigraphic units, and assess the effectiveness of differentiating between aquifer and aquitard deposits with low resistivity. The study tested the condition of perched groundwater by performed two synthetic models. These models can considerably help in the interpretation of real field measurements since they provide a reference for predicted observations under known settings. Moreover, four combined 2DERT/2DTDIP profiles were carried out in Fuka basin where the low permeability clay bands were investigated in the subsurface succession. The comprehensive examination of four 2DERT/2DTDIP lines reveals significant differences in electrical resistivity, chargeability, and normalized chargeability profiles. The 2DTDIP effectively identified the perched water zone at various depths between 20 and 30 m, indicated by high chargeability and normalized chargeability associated with clay bands which underlain the floating perched water layer. Low resistivity (11–23 Ω m) longitudinal anomalies were interpreted as saturated fracture limestone, allowing penetrating rainfalls to accumulate above this zone. High chargeability anomalies (20-25mv/v) appearing directly below fractured limestone were inferred to impermeable lenses of clay. The simultaneous interpretation of electrical resistivity and induced polarization datasets successfully differentiate between aquifer and aquitard deposits offering a highly promising strategy for identifying perched water zones at conductive at low resistivity deposits.