235-6 Understanding the geochemical processes affecting geogenic pollutants, fluoride in alluvial and hard rock aquifers in the Indo-Gangetic Plains of Northern India

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

Presenting Author:

Jyoti Kushawaha

Author:

Kushawaha, Jyoti¹

(1) Department of Environmental Studies, Ramanujan College, University of Delhi, New Delhi, Delhi, India; School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, Delhi, India,

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 Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4318

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