Microbial dynamics in porous media are drivers for a number of applications in subsurface pollutant remediation. Bioﬁlms are communities of microorganisms that are attached to interfaces (pores-grains), and embedded within a matrix of extracellular polymeric substances (EPS) that they have produced. Growing biofilms have a very small effect on porosity, but a very significant effect on the hydraulic conductivity, that reduces well beyond the value that would be obtained from the Kozeny-Carman updating formula, and further results in order(s) of magnitude increase in the estimated dispersion coefficient. We present a simplified conceptual model that is capable of providing practical expressions for the variations in conductivity and porosity. The advantage of the expressions is that they are written in terms of observables that are relatively easy to measure in the lab or the field, contrarily to most existing expressions. We then tested our simplified expressions in a number of reported experiments. Finally, we see how the simplified model captures the most significant processes of a global multi-compartment mechanistic model recently presented.
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