Use of Electrical Imaging and Distributed Temperature Sensing Methods to Characterize Surface Water-Groundwater Exchange Regulating Uranium Transport at the Hanford 300 Area, Washington
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 waterborne geoelectrical imaging, in conjunction with fiber-optic distributed temperature sensor (DTS) monitoring, to improve the conceptual model for uranium transport within the hyporheic corridor at the Hanford 300 Area. We first inverted waterborne geoelectrical (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). The spatial variability captured in the geoelectrical datasets indicates that previous studies based on borehole projections and point probing overestimate the contributing area for uranium exchange within the Columbia River at the Hanford 300 Area. The DTS data recorded on 1. 5 km of cable with a 1 m spatial resolution and 5 minute sampling interval revealed sub-reaches showing (1) high temperature anomalies and, (2) a strong negative correlation between temperature and river stage, both indicative of groundwater influxes during winter months. The DTS datasets confirm the hydrologic significance of the variability identified in the geoelectrical imaging and reveal a pattern of highly focused hyporheic 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 hyporheic exchange is observed in the DTS data where the Ringold unit is in contact with the riverbed. Our findings illustrate how the combination of waterborne geoelectrical imaging and DTS technologies can characterize hyporheic exchange in a complex, coupled river-aquifer system.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1002180
- Report Number(s):
- PNNL-SA-69319; WRERAQ; KP1702030; TRN: US1100488
- Journal Information:
- Water Resources Research, 46(10):Paper No. W10533, Vol. 46, Issue 10; ISSN 0043-1397
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AQUIFERS
BOREHOLES
CABLES
COLUMBIA RIVER
ELECTRIC CONDUCTIVITY
FLUCTUATIONS
FORECASTING
MONITORING
PERMEABILITY
POLARIZABILITY
POLARIZATION
RADAR
RIVERS
SAMPLING
SOLUTES
SPATIAL RESOLUTION
SURFACE AREA
TRANSPORT
URANIUM
Hyporheic Exchange
Uranium Transport
Geoelectrical Imaging
Distributed Temperature Sensing
water-ground exchange
uranium transport
Hanford
300 area