Characterization of Surface Water/Groundwater Exchange Regulating Uranium Transport Using Electrical Imaging and Distributed Temperature Sensing Methods
A critical challenge in advancing prediction of solute transport between contaminated aquifers and rivers is improving understanding of how fluctuations in river stage, combined with subsurface heterogeneity, impart spatiotemporal complexity to solute exchange along river corridors. Here, we explored the use of continuous waterborne electrical imaging (CWEI), in conjunction with fiber-optic distributed temperature sensor (FO-DTS) monitoring, to improve the conceptual model for uranium transport within the river corridor at the Hanford 300 Area. We first inverted CWEI (resistivity and induced polarization) datasets for distributions of electrical resistivity and polarizability, from which the spatial complexity of the primary hydrogeologic units was reconstructed. Variations in the depth to the interface between the overlying coarse-grained, high permeability Hanford formation and the underlying finer grained, less permeable Ringold formation, an important contact that limits vertical migration of contaminants, were resolved along ~3 km of the river corridor centered on the 300 Area. Polarizability images were translated into lithologic images using established relationships between polarizability and surface area normalized to pore volume (Spor). Spatial variability in the thickness of the Hanford formation captured in the CWEI datasets indicates that previous studies based on borehole projections and drive-point and multi-level sampling overestimate the contributing area for uranium exchange within the Columbia River at the Hanford 300 Area. The FO- DTS data recorded along a 1.5 km of cable with a 1-m spatial resolution and 5-minute sampling interval revealed sub-reaches showing (1) temperature anomalies (relatively warm in winter and cool in summer) and, (2) a strong correlation between temperature and river stage (negative in winter and positive in summer), both indicative of reaches of enhanced surface water/groundwater exchange. The FO-DTS datasets confirm the hydrologic significance of the variability identified in the CWEI and reveal a pattern of highly focused exchange, with exchange concentrated at springs where the Hanford formation is thick, and coinciding with a paleochannel identified in ground penetrating radar surveys at one location. No evidence for focused exchange is observed in the FO-DTS data where the Ringold unit is in contact with the riverbed or the Hanford formation is thin. Our findings illustrate how the combination of CWEI and FO-DTS technologies can characterize surface water/groundwater exchange in a complex, coupled river-aquifer system.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- DOE - SC
- DOE Contract Number:
- DE-AC07-05ID14517
- OSTI ID:
- 1020283
- Report Number(s):
- INL/JOU-10-17743; TRN: US201116%%230
- Journal Information:
- Water Resources Research, Vol. 46, Issue 10; ISSN 0043--1397
- Country of Publication:
- United States
- Language:
- English
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