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Geogenic sources of sulphate are sulphur‐bearing minerals (e.g. gypsum, anhydrite, and pyrite (Grützmacher et al. 2013). Naturally occurring sedimentary rocks containing sulphur are pyrite (FeS₂) and gypsum (CaSO₄.2H₂O) (Berner 1987; Gourcy et al. 2000). Oxidative weathering of pyrite occurring in alluvial sediments is also one of the causes of high SO₄²⁻ in water (Raju et al. 2011).

Sulphuric acid reacts with calcium carbonate found in weathered zones and produces calcium sulphate, given by the following reaction:

Factors influencing the concentration of sulphate are sulphate‐rich minerals and reducing condition in the aquifer material (Grützmacher et al. 2013)