Strategies to characterize the geochemical interrelationship between coastal saline groundwater and seawater

Abstract Groundwater contamination by the adjacent seawater has been a global problem. To address the process and evolution of salinity in groundwater, different procedures such as major ion ratios, standard plots, geophysical techniques, isotopic techniques, and modelling methods were adopted. It i...
Ausführliche Beschreibung

Abstract Groundwater contamination by the adjacent seawater has been a global problem. To address the process and evolution of salinity in groundwater, different procedures such as major ion ratios, standard plots, geophysical techniques, isotopic techniques, and modelling methods were adopted. It is difficult to distinguish the groundwaters’ with salinity, similar or greater than the seawater by adopting major ions. Saline to hypersaline conditions are reported in coastal groundwater of the arid regions. In order to address the sources of salinity, evolution and geochemical nature, groundwater samples were collected near the shore along with adjacent seawater. The ion-ratio and the Piper diagram did not show a clear demarcation between groundwater and seawater, but the fact that seawater values were within a narrow range than the groundwater. Whereas the Cl/Br and Br/Si ratios, thermodynamic stability plots of K-Silica system, Plagioclase stability and carbonate system with respect to $ logpCO_{2} $ reflected geochemical variation between the seawater and groundwater samples. Since the silica values of seawater samples were lesser, they proved to be a significant tracer to characterize the non-contaminated groundwater samples. The seawater–groundwater interaction was inferred from the study and probable locations of SGD were identified. The evolution mechanism of the brine composition with the present scenario was studied considering the saturation states of halite, silicates, carbonate and sulfate minerals. It was identified that the evolutionary pathway of brine from groundwater composition is governed by the Ca ion, which is a common ion for most of the carbonate and sulfate minerals. The groundwater chemistry indicates the Cl-$ SO_{4} $ brine evolution pathway leading to the formation of Mg-$ SO_{4} $ brine. Thus, the study proves that ratios of Cl/Br, Br/Si, thermodynamic stability plots with respect to silicate minerals and $ logpCO_{2} $ along with saturation states of minerals can serve as significant tool to characterize the hypersaline groundwater. Ausführliche Beschreibung