Hydrogeochemistry of high fluoride groundwater in hard rock aquifer in a part of Dharmapuri district, Tamil Nadu, India

Fluoride is one of the important ions that affect the groundwater quality. F− concentration above 1.5 mg/L in drinking water affects teeth and bones of humans. Usually the F− concentration in groundwater is controlled by local geological setting and climatic condition of an area. The present study aims to assess the hydrogeochemistry of groundwater in Vaniyar River basin, Dharmapuri district and to understand the F− abundance in groundwater. Forty four representative groundwater samples were collected for once in two months and analyzed for major cations and anions using ion chromatograph. The general order of the dominance of major cations is Na+ > Ca2+ > Mg2+ > K+ and that of major anions is Cl− > HCO3− > SO42− > CO3− > F−. Most of the samples are Na-Cl type and few are Ca-Mg-Cl and Ca-Cl types. The F− concentration in groundwater of this region ranges from 0.15 to 6.48 mg/L and many of the residents are affected by dental and skeletal fluorosis. The arid climatic conditions of the region, dominance of gneissic rocks and the low freshwater exchange due to periodical drought conditions endorse the presence of high F− concentration in the groundwater of the area.