Many factors affect the transport and/or transformation of metal and radionuclide contaminants found in subsurface environments. Often several competing reactions occur simultaneously and/or produce intermediates of undetermined stability, further complicating overall quantitative descriptions of reactive transport. Additionally, at many DOE sites, DOE-relevant contaminants are found under unusual conditions of pH, ionic strength and redox potentials, and in unusual mixtures. These extreme conditions attenuate as the contaminants travel down gradient resulting in a change in the transport behavior of contaminants. Likewise, various in situ remediation techniques produce changes in local geochemical conditions in groundwater or vadose zone settings that directly influence contaminant transport. Also, the metabolic activity of subsurface microorganisms or biofilm communities can profoundly change the geochemical character of contaminants and subsurface materials, either intentionally as part of a remediation technique or as a consequence of the local subsurface conditions.
The ERSP seeks understanding of the most important of the myriad biological and abiological interactions that affect contaminant transport in subsurface environments. This requires the identification and prioritization of key biogeochemical processes needed to predict the extent and rate of reactions affecting contaminant transport at DOE sites. Insight gained at the molecular scale should be used to interpret or predict processes occurring at larger scales and ultimately along groundwater flowpaths in the subsurface. Refinement of conceptual and/or computational models of contaminant transport based on new geochemical understanding of contaminant mobility and insight of cellular metabolic processes at the microbe-mineral interface is of interest. The emphasis of this science element is on understanding the integral relationships among biological and geochemical processes influencing contaminant transport and/or remediation.