Vertical electrical sounding for mapping saline water intrusion in coastal aquifers of Nagapattinam and Karaikal, South India

Geophysical investigations covering vertical electrical sounding (VES) has been employed in Nagapattinam and Karaikal coastal aquifers to isolate the sub-surface saline water intrusion. A total of 32 soundings using Wenner configuration were attempted and data were processed using IPI2WIN software. The investigations demarcated subsurface lithology intruded by saline water on the basis of resistivity signatures. Higher resistivity values (>35 Omega m) isolates aquifers free from pollution and lower resistivity values (<0.5 Omega m) indicate contaminated nature of the aquifers due to saline intrusion. The resistivity cross section separate depth between 10 and 30 m composed of sandstone with lower resistivity values (0.72-5.38 Omega m) indicating the saline nature of the aquifers. The iso-resistivity map developed for five layers isolate saline water intrusion from the first to the fifth layer in the same locations signifying the unwise withdrawal of groundwater have impacted the aquifers resulting in saline water intrusion.