LABORATORY TESTS ON THE OCCURRENCE OF FLUORIDE RICH GROUNDWATER OF TONO AREA, JAPAN

Abstract

High concentration of fluoride ion up to 12mg/l is observed in deep groundwater at the Tono area, Japan. A simple but general method to evaluate the occurrence of high fluoride ion concentration in groundwater has reported in this study. Our method based on the water-rock interaction test using different sizes of granite powders sampled from a boring core drilled at the site. Results indicated that, the weathering of granitic rock might be one of the key components for changing the fluoride ion concentrations. And also the increase of the reaction time led to enhance leaching of the fluoride ion from granite.
To deduce the contribution of the co-existence of the chemical parameters, which affected on the change in the fluoride ion concentration, a stochastic model was developed. This model shows significant evaluation of the water-rock interaction test with the chemical data of a low Na- (Ca) -Cl water-type. Results from our stochastic model indicated that the approximation reaction time of the water-rock in the granitic groundwater was about 300 days at this region.