Chapter 10 - Sulfate-Reducing Bacteria in the Zero Valent Iron Permeable Reactive Barrier at Fry Canyon, Utah

Abstract

This chapter presents a study in which a zero valent iron (ZVI) permeable reactive barrier (PRB) was installed in a shallow, colluvial aquifer contaminated with uranium in Fry Canyon, Utah, in September 1997. Aerobic and anaerobic iron corrosion reactions in the ZVI PRB have created a highly reducing, oxygen-depleted, and hydrogen gas-enriched geochemical environment in the PRB that is favorable for sulfate-reducing bacteria (SRB). Stable sulfur isotope, microbiologic, and geochemical evidence indicates that SRB are active in the ZVI PRB. The stable sulfur isotope and SO42– data from wells in the ZVI PRB and a downgradient well show that sulfur is removed by DSR through a Rayliegh-type distillation process. The enrichment factor computed from the Rayleigh plot is close to the values measured in other field investigations of DSR in groundwater systems. The thermodynamic speciation calculations and stable sulfur isotope data indicate that sulfide precipitation is the only sink for sulfur in the PRB. The distribution of SO42- concentrations indicates that most of the sulfide precipitation is occurring in the first 0.15 m of the PRB.