Science Focus Area: SSRL Environmental Remediation Program
SSRL Environmental Remediation Science Program
The SSRL Environmental Remediation Science Program is a DOE-BER funded national laboratory SFA (scientific focus area) program. We are a multidisciplinary group of collaborators based at SLAC, leading universities, and partners at other U.S. national laboratories. Our research program is focused on the DOE mission of developing more advanced models for the movement of subsurface contamination. The team has unique and world-class strengths in geochemistry and microbiology, synchrotron-based techniques, advanced lab-based spectroscopy techniques, and lab- and field-based biogeochemical methods. Integration of the expertise and methodologies of the group produces a nimble and effective research organization that can innovate new approaches and produce breakthrough discoveries.
Site characterization, remediation, and closure
The SLAC-SFA program will also support site-specific research contaminant remediation and transport research at sites of interest to the U.S. Department of Energy, including those at Hanford, Washington, Rifle, Colorado, Yucca Mountain, Nevada, and Fry Canyon, Utah.
Mission and Expected Outcomes
The mission of the SLAC SFA program is to contribute enduring, fundamental scientific knowledge about molecular-scale biogeochemical processes that control the stability and rates of subsurface contaminants and underpin modern remediation science. A major focus of this effort is to understand factors controlling the long-term success of simulated uranium reduction. Research conducted by this project will lead to enhanced remediation of subsurface uranium contamination, accelerated clean-up and closure of contaminated sites, and to increased public and regulatory acceptance of pathways to site closure. This research program will also help to preserve and protect critical water supplies that are under escalating threat from climate change.
Funding
The SLAC-SFA program is funded by the U.S. Department of Energy, Office of Biological and Environmental Research, Climate and Environmental Sciences Division.
SSRL is funded by DOE-BES.
The Need for Molecular-Scale Science
Reactions that occur at the molecular scale play crucial roles in controlling the behavior and toxicity of uranium contamination in the subsurface. Molecular-scale processes involving "environmental solid phases" are particularly important because they can remove uranium from groundwater for long periods of time. Environmental oxide solids moderate uranium migration in several fashions, including: absorption, oxidation or reduction, or incorporation into solids.
- Adsorption is the bonding of ions to surfaces of solids via covalent or electrostatic interactions. This process slows contaminant migration in aquifers, but the sorbed contaminants can be released relatively quickly if chemical conditions in the aquifer change.
- Oxidation or reduction (gain or loss of electrons resulting in a change in contaminant oxidation state) of contaminants can occur by reaction with solids such as iron oxides. Changes in oxidation state are accompanied by dramatic changes in the bioavailability and migration of contaminants in aquifers. Ideally, such reactions render contaminants less bioavailable and less mobile.
- Incorporation into solids: Entrapment of contaminants into insoluble solid phases, such as uraninite or iron oxides, is highly desirable because the contaminants thus sequestered are stable and slow to be released if aquifer chemical conditions change.
Two types of environmental solids of particular importance to this project are uraninite (UO2 + X, 0 ≤ X ≤ .25) and iron oxides. The environmental stability of uraninite and iron oxides, and hence their ability to serve as long-term sinks for uranium, is controlled by their molecular-scale structures and compositions. When uranium is released, the rates are governed by the nature of their solid-water interfaces. A robust understanding of the fundamental "structure-composition-property" relationships of these complex environmental solids is needed to develop accurate models subsurface uranium migration and cost-effective subsurface remediation and site closure strategies.