Oak Ridge National Laboratory has initiated a research project whose goal is to provide a mechanistic understanding of the linkages among ground water flow, lithology, biogeochemical processes, and the metabolic activity of microorganisms that limit the fate and transport of metal and radionuclide contaminants in subsurface environments.

Oak Ridge National Laboratory has initiated a research project titled, “Multiscale Investigations on the Rates and Mechanisms of Targeted Immobilization and Natural Attenuation of Metal, Radionuclide and Co-Contaminants in the Subsurface.” The effort began in 2007, and its goal is to provide a mechanistic understanding of the linkages among ground water flow, lithology, biogeochemical processes, and the metabolic activity of microorganisms that limit the fate and transport of metal and radionuclide contaminants in subsurface environments.

This research project is motivated by the need to a) understand the limits of natural processes in attenuating contaminant plumes, b) delineate uncertainties in how recharge events affect subsurface transport of contaminants, and c) define the level of source zone mitigation that is required to protect human health and the environment. Because the results of this research will improve our ability to predict the feasibility of natural attenuation of contaminant plumes and the impact of source zone remediation at multiple scales, the research will provide information to aid decision-making about remediation measures that may be required for effective long-term stewardship.

The primary objective of the project is to advance the understanding and predictive capability of coupled hydrological, geochemical and microbiological processes that control the in-situ transport, remediation and natural attenuation of metals, radionuclides and co-contaminants at multiple scales ranging from the molecular to the watershed. The research focuses on determining the key coupled hydrobiogeochemical factors such as pH, electron donor utilization, and redox conditions along contaminant pathways and within specific transition zones that control the fate and transport of uranium, technetium and co-contaminant nitrate within spatially distributed source zones and ground water plumes. Because remedial decisions are made at the watershed scale, investigating and understanding these processes at this scale are necessary for making informed remedial decisions. While natural processes at several uncontaminated watersheds are being investigated, there are no comparable watershed-scale contaminated sites where contaminant fate and transport issues are being investigated. The Oak Ridge Field Research Center (ORFRC) is the first watershed-scale research facility for multi-institutional, multidisciplinary investigations of contaminant issues.

The specific objectives of ORFRC research:

• quantify recharge pathways and other hydraulic drivers for ground water flow and dilution of contaminants along flow pathways, and determine how they change temporally and spatially during episodic events, seasonally and long term;
  
  
• determine the rates and mechanisms of coupled hydrological, geochemical and microbiological processes that control the natural attenuation of contaminants in highly diverse subsurface environments and over scales ranging from molecular to watersheds;
  
  
• explore novel strategies for enhancing the subsurface stability of immobilized metals and radionuclides;
  
  
• understand the long-term impacts of geochemical and hydrologic heterogeneity on the remobilization of immobilized radionuclides; and
  
  
• improve the ability to predict the long-term effectiveness of remedial activities and natural attenuation processes that control subsurface contaminant behavior across a variety of scales.

Anticipated research products include:

• predictive monitoring and modeling tools that can be used at sites to inform and improve the technical basis for decision-making, and to assess which sites are amenable to natural attenuation, and which would benefit from source zone remedial intervention;
  
  
• recommendations and strategies, conveyed via technical reports and stakeholder workshops, that will assist local decision-makers in making scientifically informed choices on ground water remediation actions; and
  
  
• scientific publications that convey our improved understanding of in-situ contaminant attenuation rates and mechanisms, and the long-term effectiveness of remedial activities relevant to in-situ remediation and stewardship.

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