Biogeochemical and mineralogical processes in redox dynamic groundwater systems

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INTRODUCTION**Biogeochemical redox processes are a principal control on the mobility of major and trace elements groundwater systems. These processes influence mineral stability and formation, and the chemical speciation and reactivity of redox sensitive elements. As a result, biogeochemical redox processes may promote mobilization or attenuation of major and trace elements in soils, sediments, and aquifers. Redox transitions that result from natural processes or anthropogenic activities can therefore have profound impacts on groundwater quality. Predicting and managing groundwater quality remains a significant challenge, as these impacts are often non-intuitive or poorly understood.**OBJECTIVES**Enhancing capacity to predict and manage groundwater requires a comprehensive understanding of biogeochemical and mineralogical processes and their impact on the subsurface mobility of major and trace elements. The overall objective of the proposed research program are therefore to advance understanding of biogeochemical and mineralogical processes and their impact on element mobility in redox dynamic groundwater systems. This objective will be pursued through a series experiments aimed at elucidating controls on the mobility of potentially toxic metal(loid)s in the shallow subsurface. More specifically, these experiments will examine biogeochemical and mineralogical controls on metal(loid) mobility under sulfate-reducing conditions. This research will be conducted under two principal research themes: (i) metal(loid) repartitioning during transformation of iron (hydr)oxides; and (ii) metal(loid) attenuation by biogenic zinc sulfides. **METHODS**The proposed research program will integrate a series of laboratory experiments to elucidate controls on arsenic, selenium, molybdenum, and antimony under sulfate-reducing conditions. These elements can occur at elevated concentrations in circumneutral pH groundwater impacted by metal, uranium, diamond, and oil sands mining activities. Arsenic and selenium remain significant global water quality issues, whereas concern over antimony and molybdenum in mining environments is increasing worldwide. Additionally, sulfate-reducing conditions are common to groundwater systems impacted by mining and mineral processing. Advective flow experiments will examine relationships between sulfate reduction rates and metal(loid) attenuation during iron (hydr)oxide transformations and biogenic zinc sulfide precipitation. Additionally, experiments will assess the stability of secondary minerals and attenuated metal(loid)s under transient redox conditions. Understanding these multifaceted associations is critical for predicting long-term impacts of biogeochemical redox processes on groundwater quality.**IMPACT**Several graduate and undergraduate students will receive advanced training through the proposed research program. These students will acquire knowledge and develop skills that will allow them to secure meaningful employment and become future leaders in their field. Results of the proposed research program are expected to inform ongoing development of strategies for the remediation and management of soils, sediments and aquifers impacted by mining, mineral processing, and other economic activities. Improving capacity to predict and manage groundwater quality is essential for reducing the impact of these activities on groundwater quality, ecosystem function, and human health.