A particle-based model of size or anion exclusion with application to microbial transport in porous media

This paper presents a novel approach to the representation of pore-scale exclusion processes, based on the truncation of the distribution of local dispersive displacements in a random-walk particle model. This approach increases the mean velocity of colloidal-sized particles relative to inert solute tracers, and decreases the apparent dispersion. An equivalent continuum model, with modified velocity and dispersion parameters, is also derived. Both the particle and the equivalent continuum models are applied to the results of laboratory experiments on bacterial transport in intact cores from a research site near Oyster, Virginia. The particle-based model requires only modest truncation (8% maximum) of the particle velocity distribution function to closely reproduce the significant observed decrease in bacterial arrival times relative to a bromide tracer. The approach provides a conceptually appealing and consistent means of incorporating the exclusion process into groundwater transport models.