Fluoride contamination mapping of groundwater in Northern India integrated with geochemical indicators and GIS
There are many incidents of increasing fluoride concentrations observed in India's groundwater. In the present study, the fluoride content was chemically analysed and integrated with geochemical model WATEQ4F sampled from Allahabad district, Northern India, with other water quality parameters. Geospatial technique was employed to depict the spatial distribution of fluoride concentrations, over this plain, normalized with WHO (World Health Organization) and BIS (Bureau of Indian Standards) standards represented in the form of spatially interpolated maps. Hydro-geological conditions, such as weathering, geochemical reactions, alkaline nature of water, ion-exchange and high variability in temperature range, were taken into account in describing the geo or anthropogenic contributions to fluoride in groundwater. A large database of available ancillary information on related factors, such as soil properties, geological settings and climatic and topographical information, on a local scale, were also taken into account to rationalize the results. The analysis implies that post-monsoon samples have elevated concentration of fluoride compared with the pre-monsoon samples, with several zones found severely contaminated with fluoride as compared with the set standards in both seasons. The correlation analysis revealed a high correlation of fluoride, with fluorite mineral saturation index, followed by calcite and magnesite, indicating that these minerals could be used as geochemical indicators for fluoride contaminated areas.