235 Advancing the Understanding and Management of Groundwater Pollution with Arsenic and Other Geogenic Contaminants Using Geospatial Tools, Machine Learning, and Data Science, Part I

The growing trend of data aggregation and analysis, along with emerging technologies like machine learning, has significantly improved our understanding of groundwater basins, enabling better assessments of water quality for direct consumption and treatment in groundwater supply management.

Wednesday, 22 October 2025
8:00 AM - 12:00 PM
HBGCC, 210AB

Understanding the geochemical processes affecting geogenic pollutants, fluoride in alluvial and hard rock aquifers in the Indo-Gangetic Plains of Northern India

Paper number: 235-6
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Abstract

Groundwater exposure and interaction with the constitutive rocks in the geological matrix influence the hydrogeochemistry of groundwater. Geogenic pollutants, such as fluoride in alluvial and hard rock aquifers, are natural contaminants from geological formations and processes in the Indo-Gangetic Plains of Northern and the Mahanadi River Deltaic regions of India. This study is based on groundwater samples collected and analyzed from i) alluvial and hard rock aquifers (Delhi NCR), ii) Bhadohi and Kaushambi (Uttar Pradesh), and iii) the Alluvial regions of Mahanadi River Deltaic regions of Odisha, India. Groundwater movement through alluvial sediments and hard rocks affects geogenic pollutants, depending on flow rates and hydrological connectivity. Chemical weathering of fluoride-bearing minerals in aquifers contributes to fluoride release into the groundwater. Underlying minerals, such as quartz and calcite, along with fluorite, indicate a geogenic source and aid in the origin and transport of fluoride, which directly influences groundwater chemistry. Groundwater is usually considered neutral to slightly alkaline, influenced by the influx of bicarbonate ions due to the interaction of CO2 from the soil with rainwater. Ion exchange is a critical mechanism, especially the interaction between groundwater and clay minerals. During the pre-monsoon, Na+ ions are retained in the aquifer matrix while Ca2+ is released, influencing mineral balance and contributing to fluorite dissolution. In post-monsoon, the reverse occurs where Ca2+ ions uptake facilitates fluorite dissolution and enhances fluoride due to silicate weathering. Increased evaporation concentrates Na+ ions in groundwater, which can lead to reverse ion exchange processes. This results in the release of Ca2+ ions while Na+ is adsorbed onto the aquifer matrix, controlling fluoride concentrations. This study also emphasizes nitrates, which are anthropogenic pollutants, and their occurrence can also be related to natural sources. In shallow aquifers, high nitrate levels can arise from both point and nonpoint sources. This study suggests that agriculture and irrigation do not contribute significantly to fluoride contamination in groundwater. This indicates that the sources affecting nitrate levels may be different from those influencing fluoride concentrations.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-411917

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