An integrated electrical resistivity and geochemical approach to delineate groundwater contamination due to seawater intrusion in the southern part of Mangalore, Karnataka, India

Abstract

Abstract In this paper, integration of electrical resistivity survey and chemical analyses of groundwater has been executed in Mangalore’s southern part, Karnataka to delineate seawater intrusion phenomena. About 11 locations representing different hydrogeological and geomorphological setups were selected for the vertical electrical sounding (VES) to identify the subsurface formations and the extent of seawater intrusion. With the VES, the contaminated groundwater zones and the depth to fresh and saline water interface have been demarcated. Overall, 59 groundwater samples were subjected to various geochemical analysis viz; pH, electrical conductivity (EC), total dissolved solids (TDS), salinity, total hardness, alkalinity, calcium (Ca 2+ ), magnesium (Mg 2+ ), chloride (Cl − ), sodium (Na 2+ ), potassium (K + )and sulfate (SO 4 2- ) to understand the nature of salinity in the aquifer. The geochemical analyses show that good groundwater conditions characterize the study area except for the southern part. The southern part is under the moderate to high salinity hazard risk, possibly due to its proximity to the sea and hydraulic connection with the seawater through the tidal creek. Two among the VES locations situated in this region show a saline water trend towards the bottom, and in the rest of the VES locations, a freshwater trend is encountered towards the depth.