Hydrogeochemistry of iron, manganese, sulfur and organic matter in the Fraser River Delta aquifer system

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The goal of this research is to develop a framework to understand and predict the geochemical evolution of reducing groundwater in deltaic aquifer-aquitard systems. In the Fraser River Delta aquifer system in British Columbia, owners and regulators are struggling to manage groundwater with high iron and manganese concentrations at both contaminated and undisturbed sites. It is recognized that organic matter degradation under anaerobic conditions is the key driver of the processes leading to high iron, manganese and trace elements such as arsenic. However, there is a gap in our understanding of the geochemical pathways of anaerobic degradation of organic matter, how to represent those pathways in models and how to characterize organic matter in - or ex situ so that models can be parameterized. The source of the organic matter, whether detrial sedimentary organic matter or surface derived from ponds or soils is not known in many cases. The processes of anaerobic organic matter degradation are coupled to the reduction of phases of iron, manganese and sulfur and cannot be examined in isolation. An integrated field - laboratory - modeling research program is proposed here. The research field site is in the Fraser River Delta system in Vancouver BC. The methodology hinges upon four components: 1) field characterization of natural systems; assessment and development of characterization strategies; 2) mineralogical and biogeochemical analysis of samples; 3) laboratory experiments under controlled conditions; and 4) mechanistic modeling to evaluate hypotheses at the field scale, to integrate and to interpret data. The framework developed here will be useful in application to engineering problems such as remediation and environmental assessment and improve management of undisturbed and contaminated sites. The research will be applicable to other settings such as the oil sands of Alberta, shale gas developments, and the great deltas of South Asia.