Geochemistry of Fluoride Rich Groundwater in a Weathered Granitic Rock Region, Southern India

Groundwater used for drinking should contain all ions within the prescribed limits for drinking purpose proposed by various health organisations. Keeping this in mind, this study was carried out with an objective to understand the present status of fluoride occurrence in groundwater, its spatiotemporal variation and sources in a part of Nalgonda district, Andhra Pradesh, India. Groundwater samples were collected and monitored for fluoride concentration in forty-five wells from March 2008 to January 2010. The concentration of fluoride in groundwater varied from 0.07 to 8.8 mg/l. The spatial variation in groundwater level and fluoride concentration indicated that fluoride concentration increases along the flow direction. The vertical variation in fluoride concentration indicated that the fluoride concentration was relatively higher in wells having a depth ranging from 5.1 to 10 m, i.e. wells penetrating up to the weathered part of the formation had more concentration of fluoride. Granitic rocks rich in fluoride and application of fertilisers containing fluoride were the main causes for fluoride contaminated groundwater in this area. This two-year study carried out by regular collection of samples once every two months showed that only 55 km(2) of the total 724 km(2) considered for the study had groundwater suitable for drinking and domestic purpose with respect to fluoride. It is very important to adopt groundwater management measures at the earliest to improve the groundwater quality in this area as the local people depend on groundwater for their everyday needs.