Diffusion/dispersion-limited mixing and reactions in saturated homogeneous and heterogeneous porous media

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Natural attenuation (mainly biodegradation) of organic pollutants in groundwater often depends on mixing of electron donors and acceptors. Mixing in the field is the result of transverse dispersion, which is a function of groundwater flow velocity, the typical length scale in the aquifer (e.g. grain size) and aquifer heterogeneities, and the dynamics of the natural flow system. The objectives of this proposal are twofold: 1) to investigate dispersion-limited reactions in well-controlled bench-scale experiments and 2) to use numerical models to elaborate how heterogeneities and transient conditions at the field scale (in time and space) influence the overall natural attenuation rates of organic pollutants in groundwater. Example reactions limited by transverse dispersion will be investigated in the lab in high resolution in time and space using innovative optical online analysis (with TP 5). The influence of grain scale heterogeneities and transient flow conditions will be quantified and the results will be used for validation of a numerical transport/reaction model (PHT3D). The model accounts for advection, dispersion, sorption, biodegradation (incl. kinetics) and is coupled to a geochemical code (PHREEQC). The validated code is used for scenario specific modeling at the field scale.