An exploration of stream-riparian groundwater exchange during baseflow recession: Integration of hydrologic and geophysical data
Kamini Singha, Professor and Ben Freyrear Endowed Chair for Innovation and Excellence, Colorado School of Mines
Abstract: “Anomalous” solute-transport behavior, not explained by classical mathematics, has been observed at research and aquifer-remediation sites in diverse hydrogeologic settings. Anomalous behavior such as concentration rebound, long breakthrough tailing, and poor pump-and-treat efficiency have been explained by dual-domain mass transfer, where transport occurs between (1) a mobile domain, which consists of well-connected pores and fractures in aquifers, or a stream in watershed systems, and (2) a less-mobile domain, which consists of poorly connected pores and dead-end fractures, or a hyporheic zone. Despite recognition of the importance of non-Fickian transport, verification of its occurrence and inference of controlling parameters remain problematic. Conventional geochemical measurements preferentially sample from the mobile domain and thus provide only indirect information for the immobile domain and exchange between domains. Here, I present a petrophysical framework, experimental methodology, and analytical expressions that can be used to infer mass-transfer parameters from co-located breakthrough curves of mobile concentration and near-surface geophysical methods, specifically electrical resistivity (ER). In particular, I’ll focus on stream-groundwater interactions, which are critical to ecosystem structure and function and water quality in many streams. We’ll explore the controls on valley-bottom subsurface hydrology, which influences hyporheic exchange, using tracer tests and ER to inform on groundwater-surface water exchange. Traditional characterization of hyporheic exchange (connectivity between streams and near-stream aquifers) relies upon solute tracer studies and a spatially sparse set of observations in streams and monitoring wells. ER methods image hyporheic exchange in both two and three-dimensions, and identify flowpaths at different temporal scales of stream connectivity. These data are an improvement over traditional methods, which would otherwise provide only reach-averaged values, or single observations in space. Temporal moments of solute and ER data are used to compress trends into descriptive statistics and identify dominant solute transport processes (e.g., transient storage dominated, advection dominated, etc.).
About the Speaker: Kamini Singha is the Ben Fryrear Endowed Professor for Innovation and Excellence at the Colorado School of Mines, and serves as the Associate Department Head of the Department of Geology and Geological Engineering. She worked at the USGS Branch of Geophysics from 1997 to 2000, and served on the faculty of The Pennsylvania State University as an assistant and then associate professor from 2005 to 2012. Her research interests are focused in hydrogeology and environmental geophysics. Dr. Singha is the recipient of an NSF CAREER award, was awarded the Early Career Award from the Society of Environmental and Engineering Geophysics in 2009, served as the National Groundwater Association's Darcy Lecturer in 2017 and became a GSA Fellow in 2018. She earned her B.S. in geophysics from the University of Connecticut in 1999 and her Ph.D., in hydrogeology, from Stanford University in 2005.