ABSTRACT
Aquifers in granitic terrenes are known to have fluoride content almost at all levels and often much beyond the permissible limit. The Fluoride content of groundwater in granitic aquifers is mainly due to dissolution process during rock-water interaction. However, the high variability observed in the fluoride content arises from the fact that fluorine bearing minerals present are not uniformly distributed in the host rock and also the physico-chemical properties of water present varies enormously. Since fluoride content is an important parameter in drinking water and is desired to be maintained in a specified range, repeated sampling of water in a small watershed in a granitic aquifer have been carried out. Regarding the spatial variability, it has been observed that wells surrounding the villages have comparatively high fluoride content baring one of the highest value obtained from a reserve forest area. Although, the fluoride content is the result of natural geo-chemical contamination but with the given variation the anthropogenic activities such as use of pesticides and fertilizers could not be ruled out. In this study particularly the variation of fluoride contents with time in the same wells have been analysed. Contrary to what could be thought in the natural conditions, fluoride contents have cyclic variation in time unusually following the water levels. The results indicate that the aquifer thickness in contact with water in a well, dissolution rates as well as nature of flow are the important factors affecting the variability of the parameter with time.
