High fluoride in groundwater of an industrialized area of Eastern India (Odisha): inferences from geochemical and isotopic investigation

An assessment of fluoride distribution in groundwater of an industrialized area (Talchir), Odisha, India, was carried out to understand the potential sources and processes. This study is significant as the water resources are being endangered by the mining and other industrial activities in this region. High concentration of fluoride (4.4 mg/L) was observed in groundwater of this area, which was attributed mainly to mining activities. Additional source for high fluoride is the basement granitic rock containing fluoride bearing minerals like amphibole, biotite and fluorite. The dominant chemical types are found to be Na-Ca-HCO3, Na-Mg-HCO3, Ca-Mg-HCO3 and Ca-Na-HCO3. The groundwater facies variation was found in accordance with the local lithology. There was no marked difference in the fluoride concentration of groundwaters between near and far off mining zone. Geochemical modeling indicated precipitation of calcite and dolomite as the driving force for the release of fluoride from the formation. In addition to the precipitation of calcite and dolomite, evapotranspiration also contributes to high fluoride in groundwater. Environmental stable isotopes inferred that there was no clear isotopic distinction between high and low fluoride groundwater and the groundwater was found to be evaporated. Environmental tritium data suggested that the groundwater was modern and fluoride enrichment was facilitated by long residence time of groundwater. Statistical methods also corroborate the geochemical and isotopic inferences. The study highlights that natural geogenic source is the main cause for high fluoride in groundwater refuting earlier theories that attribute mining activities as the only source for high fluoride in this region.