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 will perform 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).
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.
The SFA is building on established areas of PNNL expertise in geochemistry, microbiology, 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. It will also use samples of opportunity from the Rifle Integrated Field Research Challenge site. The research theme of the IFC 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 IFC efforts are fully complementary across multiple scales.
The SFA consists of 11 projects involving 12 external collaborators within microbial ecology, molecular-scale mechanisms, pore-scale coupled processes, reactive transport science, multi-scale reactive transport models, in situ structures and reactive transport properties. It has four hypotheses and Hanford-relevant contaminant scenarios and relies strongly on the Environmental Molecular Sciences Laboratory at PNNL for fundamental science capabilities as well as the Advanced Photon Source (APS) at Argonne National Laboratory and the Stanford Synchrotron Radiation Laboratory (SSRL).
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.