Assessment of Groundwater Quality with respect to Fluoride in Somavathi River basin, Ananthapuramu District (Andhra Pradesh), India

The hydrogeochemicalstudy was conducted both in the pre and post monsoon seasons of Somavathi River basin (India) to know the principal controlling mechanisms of fluoride in groundwater. The fluoride concentration along with some physico-chemical parameters in groundwater, were determined using established standard practices. Petrographic observations of host rocks coupled with molar ratios of chemical species studies exemplify that weathered material developed over the granitegneiss, mica-schist, amphibolites, granitic intrusive and pegmatite veins due to weathering and extensive water-rock interaction, resulted into higher concentration of fluoride in groundwater. The fluoride concentrations in the villages varied from 1.5 to 2.90 mg/L with highest fluoridevalue at Nallamada (2.90 mg/L) and lowest at 1.5. mg/Lin the pre and post monsoons. From the study, it is found that the alkaline pH and high bicarbonates are responsible for release of fluoride bearing minerals into groundwater. The major water facies were Ca-Mg-Cl and Ca-HCO3. Moreover, the arid climate of the region,the granitic rocks and the low freshwater exchange due to periodical drought conditions,are factors responsible for the higher incidence of fluorides in the groundwater resources. In addition, most wells appear suitable for irrigation activities according to RSC, % Na and SAR.