Geophysical and hydrogeological investigation for the saline water invasion in the coastal aquifers of West Bengal, India: a critical insight in the coastal saline clay-sand sediment system.

The Digha-Shankarpur area in West Bengal suffers from the problem of saline water intrusion in the near-surface to shallow subsurface aquifers. In the present study, geophysical surveys were conducted and integrated with measured hydrogeological parameters to delineate the possible locations of saline water-invaded zones in the shallow aquifers. One hundred eighty-eight groundwater samples were collected, and parameters like salinity, EC, total dissolved solids (TDS), pH, temperature, and water level were measured. The geophysical survey, such as resistivity profiling, self-potential, and electrical resistivity imaging techniques, was applied. High TDS, salinity, and EC were observed in various places. Resistivity profiling survey indicates a low resistivity zone (< 10 Ωm), self-potential anomaly indicates a positive anomaly and resistivity imaging survey indicated very low resistivity zones (0-3 Ωm) in near-surface to shallow subsurface locations which are concurrent with the other coastal aquifers in the eastern part of India. These low resistivity zones are interpreted as saline water intrusion zone mixed with clay/sand layers up to a depth of 15 m possibly due to the ingression of seawater and also due to anthropogenic activities. Hence, protection from seawater intrusion from the canals into the coastal aquifers (shallow and deep) and human-made activities should be restricted to minimize the effect of saline water pollution.