MICROBIALLY-MEDIATED PYRITE OXIDATION IN THE TUNNEL CITY GROUP AND WONEWOC FORMATION SANDSTONES OF TREMPEALEAU COUNTY, WI

2019 was designated as the year of clean drinking water for Wisconsin. Along with anthropogenically-sourced contaminates, naturally occurring contaminates should also be considered. Metal-sulfide mineral oxidation in circumneutral pH environments is a relevant groundwater quality concern for Wisconsin’s sandstone and carbonate Cambrian-Ordovician aquifer system. This aquifer system has been observed to host varying abundances of metal-sulfide minerals, such as pyrite, across Eastern, Western, and South-Central Wisconsin, USA. When these sulfide-bearing geologic units are exposed to oxygenated groundwater or earth-surface conditions, they can oxidize and generate acidity, releasing metals into the aqueous environment.

Although pyrite dissolution in the context of acid mine drainage has been extensively studied, the role of bacteria in mediating pyrite oxidation at circumneutral pH is not well understood. It has recently been shown that chemolithotrophic bacteria can accelerate neutral-pH, aerobic oxidation of both synthetic and specimen pyrite up to 10-fold relative to abiotic controls. However, to our knowledge, no previous studies have documented the influence of biological activity on pyrite oxidation with native groundwater, subsurface materials, and bacterium.

We carried out microcosm experiments with native geologic material of the Tunnel City Group (TCG) glauconitic and dolomitic sandstone, and the Wonewoc Formation (WF) quartz sandstone from Trempealeau County, WI, each containing about 3% by weight or less of nodular or disseminated pyrite, and native groundwater from those geologic units as the aqueous medium and the bacterial inoculum. Preliminary results from our study supports our hypothesis that the oxidation of sulfide minerals in the TCG and WF materials is enhanced in the presence of iron and sulfur oxidizing microorganisms. These findings will shed light on the oxidation kinetics of natural sulfide minerals in sandstone aquifers in Wisconsin and other like-aquifer, geochemical, and geomicrobial subsurface systems.