GEOELECTRICAL MONITORING OF SOLUTE TRANSPORT IN DUAL-DOMAIN MEDIA: A REVIEW

Dual-domain media pose major challenges to the reliable design of groundwater remediation systems, efficient management of groundwater resources, and basic understanding of solute transport in aquifers and the hyporheic zone. Dual-domain systems comprise both mobile and immobile porosity, the latter of which is largely invisible to conventional fluid sampling that draws preferentially from the mobile pore space. Quantification of immobile contaminant mass is problematic, and understanding the release of immobile solutes depends on the rate of mobile/immobile exchange, which is difficult to measure directly. In the context of an aquifer-storage recovery experiment in 2007, geoelectrical measurements were first shown to be sensitive to immobile concentration. Combining measurements of bulk electrical conductivity and fluid electrical conductivity provided new insight into immobile porosity and the rate of exchange with mobile porosity. Over the last ten years, a growing body of laboratory, field-experimental, and modeling studies have established the sensitivity of geoelectrical measurements to ionic tracer concentration in immobile porosity. Numerical simulations at the macro and micro scales have demonstrated the value of combining conventional fluid sampling and geoelectrical measurements and led to development of new approaches to analyze such datasets and estimate controlling parameters, i.e., immobile porosity and exchange rate coefficients. We review a decade of research leading to new petrophysical frameworks, experimental methodologies, and data analysis approaches supporting the application of geoelectrical methods to understand solute transport in dual-domain media.