172-11 Geochemical Evolution and Mobility of Geogenic Contaminants in a Hydrothermally Mineralised Crystalline Aquifer

Session: Environmental Geochemistry and Health (Part II)

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Hydrothermally mineralised crystalline aquifers are important sources of naturally occurring groundwater contamination, yet the geochemical processes governing the behaviour of multiple geogenic contaminants remain poorly understood. This study investigates the sources, release mechanisms, and transport of arsenic (As), cadmium (Cd), lead (Pb), and fluoride (F⁻) in the fractured crystalline aquifer of the Dongargarh–Kotri region, central India. Groundwater is enriched in arsenic, cadmium, and lead, whereas fluoride generally remains within drinking-water guideline limits. Petrographic and SEM–EDS analyses identify a hydrothermal assemblage of sulfide- and fluoride-bearing minerals as the primary geogenic source of these contaminants. Hydrogeochemical modelling indicates that these minerals remain thermodynamically unstable under present groundwater conditions, favouring continued contaminant release through sulfide weathering and mineral dissolution. Although the contaminants originate from a common hydrothermal source, they exhibit distinct geochemical behaviours. Arsenic transport is controlled primarily by redox reactions and limited attenuation by iron oxyhydroxides; cadmium remains highly mobile because of weak adsorption; lead mobility is moderated by carbonate complexation and secondary mineral equilibrium, whereas fluoride is governed by fluorite dissolution and calcium availability. Health risk assessment identifies arsenic as the dominant carcinogenic contaminant and, together with cadmium, as the principal non-carcinogenic hazard, particularly for children. These findings establish a source–pathway–mobility framework for understanding multi-contaminant groundwater systems and provide insights for improved groundwater quality assessment and management in hydrothermally mineralised crystalline aquifers.

Keywords: Geogenic contamination;  Hydrothermal mineralisation; Crystalline aquifer; Hydrogeochemistry; Groundwater mobility

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