| Abstract Submission No. | ABS-3.1-0152 |
| Title of Abstract | Geochemical Characterization, Source of Fluoride Enrichment, and Groundwater Vulnerability in the Crystalline Granitic Terrain |
| Authors | Shahwaz Khan*, P.D. Sreedevi, Tanvi Arora |
| Organisation | National Geophysical Research Institue, Uppal Road, Hyderbad, Tel |
| Address | National Geophysical Research Institute (NGRI), Hyderabad Hyderabad, Telangana, India Pincode: 500007 E-mail: khanshahwaz8@gmail.com |
| Country | India |
| Presentation | Poster |
| Abstract | Groundwater in the Maheshwaram watershed, South India, is chronically affected by elevated fluoride (F⁻) levels; However, the mechanisms of releasing it, its controlling mineral sources, and the spatial vulnerability remain poorly characterized. This study integrates multiple approaches, such as hydrochemical analysis, mineralogical characterisations, and GIS-based DRASTIC modelling, to reveal the geogenic factors driving F⁻ enrichment in a crystalline granitic aquifer. A total of 46 pre-monsoon and 47 post-monsoon groundwater samples were analyzed for physico-chemical parameters, while representative rock samples were examined to link F-bearing minerals with groundwater chemistry. F⁻ concentrations ranged from 0.89 to 3.50 mg/L (pre-monsoon) and 0.83 to 3.72 mg/L (post-monsoon), with 32% and 30% of samples surpassing the WHO threshold of 1.5 mg/L. The hydrochemistry is primarily influenced by rock-water interactions and ion exchange mechanisms, resulting in alkaline conditions that promote F⁻ mobilization. PHREEQC modeling showed that groundwater is undersaturated in fluorite and oversaturated in calcite, a state that facilitates the release of F⁻ via calcite precipitation. Principal Component Analysis (PCA) and Cluster Analysis (CA) found silicate weathering and ion exchange as the principal factors for F⁻ enrichment. Mineralogical studies (Microscopic, Model and Electron Probe Microanalysis) confirmed the presence of F-bearing minerals such as biotite, epidote, apatite, sphene, and allanite. The alteration of these minerals, particularly the chloritization of biotite, is recognized as a principal release mechanism. The DRASTIC model delineated 'high' to 'very high' vulnerability zones covering 57% of the watershed, demonstrating a good correlation with reported high-F⁻ regions. These areas are defined by shallow water tables and the existence of F⁻-rich lithologies. By integrating hydrochemical, mineralogical, and aquifer risk mapping, this research provides a comprehensive framework for understanding fluoride mobilization and offers guidance for targeted management and sustainable use of groundwater in fluoride-affected crystalline regions. |
| Keywords | Fluoride, PHREEQC, PCA, Groundwater-rock interaction, Weathering and alteration, Ion Chemistry |