Geochemical assessment of fluoride enrichment and nitrate contamination in groundwater in hard-rock aquifer by using graphical and statistical methods

Abstract

This systematic study was carried out with objective to delineate the various sources responsible for $\hbox {NO}_{3}^{-}$ contamination and $\hbox {F}^{-}$ enrichment by utilizing statistical and graphical methods. Since Central Ground Water Board, India, indicated susceptibility of $\hbox {NO}_{3}^{-}$ contamination and $\hbox {F}^{-}$ enrichment, in most of the groundwater, $\hbox {NO}_{3}^{-}$ and $\hbox {F}^{-}$ concentration primarily observed ${>}45$ and ${>}1.5~\hbox {mg/L}$, respectively, i.e., higher than the permissible limit for drinking water. Water Quality Index (WQI) indicates ${\sim }22.81\%$ groundwater are good-water, ${\sim }71.14\%$ groundwater poor-water, ${\sim }5.37\%$ very poor-water and 0.67% unsuitable for drinking purpose. Piper diagram indicates ${\sim }59.73\%$ groundwater hydrogeochemical facies are Ca–Mg–$\hbox {HCO}_{3 }$ water-types, ${\sim }28.19\%$ Ca–Mg–$\hbox {SO}_{4}$–Cl water-types, ${\sim }8.72\%$ Na–K–$\hbox {SO}_{4}$–Cl water-types and 3.36% Na–K–$\hbox {HCO}_{3 }$ water-types. This classification indicates dissolution and mixing are mainly controlling groundwater chemistry. Salinity diagram indicate ${\sim }44.30\%$ groundwater under in low sodium and medium salinity hazard, ${\sim }49.66\%$ groundwater fall under low sodium and high salinity hazard, ${\sim }3.36\%$ groundwater fall under very-high salinity hazard. Sodium adsorption ratio indicates ${\sim }97\%$ groundwater are in excellent condition for irrigation. The spatial distribution of $\hbox {NO}_{3}^{-}$ indicates significant contribution of fertilizer from agriculture lands. Fluoride enrichment occurs in groundwater through the dissolution of fluoride-rich minerals. By reducing the consumption of fertilizer and stress over groundwater, the water quality can be improved.