Electrical Resistivity and Induced Polarization signatures to delineate the near-surface aquifers contaminated with seawater invasion in Digha, West-Bengal, India

Abstract

The Digha-Shankarur-Tajpur-Mandarmani (DSTM) area in West-Bengal is well known for seawater invasion in shallow aquifers. In the present work, geophysical investigations such as Electrical Resistivity Imaging (ERI) and Induced Polarization (IP) data were used to delineate the possible zones of shallow aquifers contaminated with seawater. Smoothness-constrained least square and unstructured grid-based finite element methods were applied to interpret ERI data. The finite element method based inversion technique adopted in this study is better in terms of the final resolution of interpretation. Furthermore, the resistivity imaging survey showed low resistive zones (0–5 Ωm) in shallow aquifers. Subsequently, the IP data with low chargeability indicates probable zones of seawater invasion. These affected zones are associated mostly with clay and sandy layers up to a depth of 30 m. Moreover, the geophysical data suggests that the seawater invasion zones do not show any linear relationship throughout the area. This is mainly because the anthropogenic activities have overshadow geogenic activities. Hence, human-induced activities should be restricted in the present study area on the landward side to reduce the hazards related to seawater invasion in the groundwater aquifers in the region.