Geophysical and geochemical approach to identify the groundwater quality in Agastheeswaram Taluk of Kanyakumari District, Tamil Nadu, India

A combined study of both geoelectrical and geochemical methods was used to find the quality of groundwater in the Agastheeswaram Taluk of Kanyakumari District, Tamil Nadu, India. The vertical electrical sounding (VES) method was applied to identify the variations in electrical resistivity of the subsurface. Three to five geoelectric layers are interpreted in the study area from the observed VES data. The aquifer was mostly found in the second or third layer. Analytical results from the 14 groundwater samples collected near the VES stations are in good correlation with the VES outcomes. Also, the interpreted results of VES data collected from the field were compared with the existing subsurface data and correlation was made, which proved the consistency of the VES method. Iso-resistivity contour maps for different depths and pseudo cross sections showing the resistivity distribution with depth are prepared for detailed analysis. More than 50 % of the area is having aquifer resistivity value less than 10 Omega m. This indicates that the aquifer is found to get polluted by saline water intrusion or some other anthropogenic activities, like intense agricultural practices and poor sewage management. From the geochemical analysis of the groundwater samples, it is found that the Na+ and Cl- are the dominant cation and anion in the study area. Evaporation and rock-water interaction are found to be the major processes controlling the ion concentration in the groundwater. The results obtained from geochemical analysis are in good correlation with the VES results.