PNNL

Abstract

This paper presents a novel approach to the quantification 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 (concentration-based) model, with modified velocity and dispersion parameters, is derived. The model was applied to the results of laboratory experiments on bacterial transport in intact cores from a research site near Oyster, Virginia. The significant observed decrease in bacterial arrival times relative to a bromide tracer was closely reproduced by the particle-based model with modest degrees of truncation (8% maximum). The approach provides a conceptually consistent means of incorporating the exclusion process into groundwater transport models.