title: Transverse dispersion of non-reactive tracers in porous media: a new nonlinear relationship to predict dispersion coefficients.
abstract: Assessing the potential of natural attenuation in groundwater relies on the ability to predict and quantify the processes that occur in contaminant plumes. Transverse dispersion is a significant mass transfer mechanism for mixing of electron acceptors and donors and thus may control the lengths of steady state plumes. Laboratory experiments were carried out using a 2-dimensional acrylic glass tank filled with glass beads, quartz sand and field site material as porous media. Flow velocities and grain sizes were varied in order to cover a large range of Peclet numbers including typical field scenarios. The laboratory study was extended by a comprehensive literature search to compare the new results with earlier work. As a result we propose a new empirical relationship for prediction of transverse dispersion coefficients (Dt) which is based on the Peclet number (Pe). This new relationship indicates a nonlinear dependency on the flow velocity (nu a) and grain size (d), namely a relative decrease of the dispersion coefficient with increasing flow velocity in relatively fast flowing water: Dt/Daq=Dp/Daq+0.28(Pe)0.72 (with Pe=nu a d/Daq; Daq and Dp denote the aqueous and pore diffusion coefficients, resp.).
authors.affiliation: Center for Applied Geosciences, Tübingen University, Sigwartstr. 10., 72076 Tübingen, Germany.
authors.forename: Asa
authors.initials: A
authors.lastname: Olsson
authors.forename: Peter
authors.initials: P
authors.lastname: Grathwohl
mesh_terms: D008962:Models, Theoretical; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical