Impact of Seawater Intrusion on the Geochemistry of Groundwater of Gwadar District, Balochistan and Its Appraisal for Drinking Water Quality

Abstract

Thirty-one groundwater samples were collected from Jiwani, Ganz, Pishukan, Gwadar and Sur Bander, coastal towns of Gwadar District, Balochistan Province, Pakistan. The overall average trend of cationic and anionic distributions is found in the order of $\hbox {Na}^{+}>\hbox {Ca}^{2+}>\hbox {Mg}^{2+}>\hbox {K}^{+}$ and $\hbox {Cl}^{-}>\hbox {SO}_{4}^{2-}> \hbox {HCO}_{3}^{-}>\hbox {NO}_{3}^{-}>\hbox {CO}_{3}^{2-}>\hbox {F}^{-}$, respectively. Average ionic composition on Stiff diagram shows ($\hbox {Na}^{+}+\hbox {K}^{+})\hbox {--}\hbox {Cl}^{-}$ as one of the principal ionic pair, while ionic balance among $\hbox {Mg}^{2+}\hbox {--}\hbox {SO}_{4}^{2-}$ and $\hbox {Ca}^{2+}\hbox {--} (\hbox {HCO}_{3}^{-}+\hbox {CO}_{3}^{2-})$ have shown an imbalance. On Piper diagram, majority of the groundwater samples in the study area are of NaCl type. The $\hbox {Na}^{+}$ versus $\hbox {Cl}^{-}, \hbox {Na}^{+}/\hbox {Na}^{+}+\hbox {Cl}^{-}$ versus $\hbox {Cl}^{-}/\sum$ anions, and Cl versus $\hbox {Cl}/\hbox {HCO}_{3}$ ratios signify influence of seawater intrusion in the coastal strip of Gwadar District. The impact of seawater encroachment in the coastal regions has also been proved by hydrochemical facies evolution diagram and Piper plots. Principal component analysis reveals three major factors, whereas high positive loading of $\hbox {Na}^{+}$, $\hbox {Ca}^{2+}$, $\hbox {Mg}^{2+}$, $\hbox {Cl}^{-}$, $\hbox {SO}_{4}^{2-}$ and TDS reveal association with seawater. Potassium, nitrate and bicarbonate are in other domain; their relation with pH being rather negative. Moreover, fluoride and carbonate should be confined to separate realms, specifying of good relation among the two ions. Concentrations of nitrate and fluoride are found to be higher than the WHO permissible limit and may therefore pose a health threat to the local population.