Bacterial sulfate reduction and pyrite formation in a polluted sand aquifer

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Abstract
Profiles of water chemistry through a pollutant plume in an unconsolidated sand aquifer show depleted sulfate and enhanced bicarbonate concentrations associated with sulfidic zones in the plume. Sulfide is 34S‐depleted relative to sulfate, showing that sulfate‐reducing bacteria are responsible for sulfide production. Pyrite and elemental sulfur form in the aquifer matrix as a result of sulfate reduction. These species are 34S‐depleted relative to groundwater sulfide, indicating that they predominantly formed early during the phase of sulfate reduction. Later, reoxidation of sulfide to sulfate at the margins of the plume rather than pyrite formation appears to be the main sink for sulfide. At this stage a “steady‐state”; profile develops, with higher concentrations of relatively 34S‐depleted sulfate at the plume margins and lower concentrations of 34S‐enriched sulfate in the sulfidic zone.