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Biological Sciences

Role of Microenvironments and Transition Zones in Subsurface Reactive Contaminant Transport

Subsurface Science Scientific Focus Area (SFA)

The Subsurface Science Scientific Focus Area (SFA) is funded by the U.S. Department of Energy's Office of Biological and Environmental Research. The SFA team is performing integrated, multidisciplinary, science-theme-focused research on the role of microenvironments and transition zones in the reactive transport of technetium (Tc), uranium (U), and plutonium (Pu). The primary environmental system being studied is the groundwater-river interaction zone in the 300 area of the Hanford Site in southeastern Washington State.

Ringold Sediments
Redox boundary in Ringold sediments about 2.5 m below the Hanford-Ringold contact. The boundary is the point where oxygen and other terminal electron acceptors have been consumed by microbiologic respiration. Residual organic matter in the sediments is believed to be the electron donor for this process. This reducing zone appears to collect contaminant U(VI) that migrates from above under conditions of high groundwater uranium.ENLARGE

The SFA is building on established areas of PNNL expertise in geochemistry, microbiology, reactive transport science, and multi-scale modeling. It is closely aligned with the Hanford Integrated Field Research Challenge site as an essential location for samples and opportunities for field-scale research. The research theme of the IFRC is multiscale mass transfer controls on reactive transport. The SFA's research theme is the role of microenvironments and transition zones in reactive transport. The SFA and IFRC efforts are fully complementary across multiple scales.

The SFA consists of three theme areas involving 15 PNNL and five external principal investigators. Cohesiveness and integration is achieved by three crosscutting science elements; and an integrative, system-scale modeling activity of the groundwater-river interaction zone that involves information up-scaling, resolves broader science issues, and enhances Hanford impact.

With emphasis on the highly dynamic groundwater-river interaction zone, the overall project has a unique research footprint that is advancing science in key areas. The SFA relies strongly on the Environmental Molecular Sciences Laboratory (EMSL) at PNNL for fundamental science capabilities as well as the Advanced Photon Source (APS) at Argonne National Laboratory.

Through long and active association with the Hanford Site, the SFA researchers recognize that microenvironments and transition zones are fundamental, yet poorly understood subsurface features that merit a sizable, integrated, multidisciplinary research effort with high potential scientific impact. While this SFA focuses on Hanford, the research will be broadly applicable to DOE and other contaminated sites nationwide.

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