Determining the interaction between groundwater and saline water through groundwater major ions chemistry

SummaryIt is hypothesized that groundwater major ions chemistry can be employed to determine the interaction between groundwater (GW) and saline water/seawater (SW) in costal aquifers, and that there exists a relationship between total dissolved solids with chloride, sodium, magnesium and sulphate concentrations of groundwater. This hypothesis was tested on a watershed located along the southeastern coast of India. From empirical data collected twice during pre- and post-monsoon seasons, it was found that in both seasons, out of 99.9% of the electrical conductivity (EC) variability due to the combined effect of Na+, Ca2+ + Mg2+, SO42-, Cl−, HCO3-andNO3-, 54.0% was due to Cl− alone in pre-monsoon, and 43.1% in post-monsoon. Results of factor analysis highlighted the multi-scale control of the fluid exchange and the influence of mixing zones between groundwater and saline water. Hydrochemical processes that accompany the intrusion of seawater were identified using ionic changes. It was observed during the sampling periods that the mixing due to seawater intrusion varied from 4.82% to 7.86% throughout the watershed. Negative values of ionic change (echange) for Na+ and K+ decreased with the increasing fraction of seawater.