Geochemistry Department Core Capability:
Geochemical Transport

This effort involves simulation and study of coupled mineral-water-gas reactive transport in unsaturated porous media. The work covers infiltration/evaporation processes in the soil zone, reaction-transport processes in fractured rock under boiling conditions, injection of CO₂ in deep aquifers, hydrothermal alteration in geothermal systems, the controls on the rates of chemical weathering, and biogeochemical reaction networks in low-temperature environments. Although reaction-transport modeling and code development are the predominant activities, the group is also active in planning and executing various field and laboratory experiments focusing on the remediation of contaminated DOE sites, geothermal systems, natural analogues for nuclear waste isolation, as well as fundamental research on water-mineral interactions.  Examples of more fundamental research projects include the world’s first experimental studies using engineered microfluidic reactors to determine mineral-water reaction rates directly at the pore (mm) scale, the scale dependence of mineral-water reaction kinetics using pore network models, and the application of lattice-Boltzmann models to reaction-transport processes at the microscopic scale. 

Historically, a lot of geochemical transport work has been focused on predicting thermally driven processes accompanying the proposed emplacement of high-level nuclear waste at Yucca Mountain, Nevada, and on the understanding of the evolution of the natural hydrogeochemical system. One focus of this work was on integrating the thermal-hydrologic-chemical environment in the near field of the proposed Yucca Mountain repository with THC processes occurring inside emplacement drifts, including on the surface of the waste package (where corrosion is the main issue) and inside the waste packages (where dissolution of spent fuel is the main issue).

More recent research projects include  understanding the controls on chemical weathering. One such effort involves integration of uranium-series isotopic disequilibria with major element profiles to determine in situ reaction rates in deep-sea marine sediments. Another involves understanding the controls on, and rates of, formation of weathering rinds; this work has demonstrated the key role of reaction-induced porosity change in controlling the weathering rate.  The Geochemical Transport Group is also taking a key role in developing new-generation biogeochemical reactive transport models for application to the remediation of contaminated DOE sites.

Collaboration with other departments in ESD brings together essential pieces of the problem, including hydrological processes in the unsaturated zone, thermodynamics and kinetics of geochemical processes, and isotopic effects. More recently the group has begun studies relevant to the geologic sequestration of CO₂ and conducts hydrothermal experiments to study rates of mineral growth and dissolution under reservoir condtions of T, P and CO₂ fugacity.

Current projects include:

• Development of models for reactive-transport in unsaturated systems and co-development of the reactive-transport code TOUGHREACT
• Improved thermodynamic and kinetic databases for water-rock interaction modeling
• Modeling of CO₂ sequestration in saline aquifers
• Simulation of high-ionic-strength environments following evaporation of pore fluids around nuclear waste emplacement tunnels
• Prediction of the rate of strontium migration at the Hanford site
• Experimental and modeling studies on the scale dependence of mineral reaction kinetics
• Modeling of bioremediation field tests at the Hanford site
• Modeling biogeochemical processes affecting the transport of heavy metals in lake sediments affected by acid mine drainage
• Investigating the subsurface acidic alteration and transport of Sr-90, I-129, and U at the Savanah River site F-area
• Help in evaluating the feasibility of various (bio)remediation methods, such as the use of urease-promoted calcite precipitation for Sr sequestration in the saturated zone, and tri-ehthyl phosphate gas injection as a means to promote phosphate mineral precipitation and U-sequestration in the vadose zone.