Effect of Coefficient of Variation of Particle Size of Porous Media on Contaminant Transport

The contaminant transport in porous media is crucial for a comprehensive understanding of groundwater contamination. However, there are still inadequacies in the research concerning the effect of the coefficient of variation (COV) of particle size of porous media on the contaminant transport in the internal microscopic pore structure. A method is proposed to construct a geometric model of porous media with different coefficients of variation and consistent porosity based on a random algorithm. The groundwater flow field and contaminant concentration field in porous media are obtained by coupling the Navier-Stokes equation and the advection-diffusion equation. The uniformity of flow velocity distribution is evaluated quantitatively by introducing Christiansen uniformity coefficient. Based on the MIM (mobile and immobile) model and the ADE (advection-dispersion equation) model, the characteristics of breakthrough curves are analyzed. The results show that as the COV of particle size increases, the non-uniformity of the flow velocity distribution is enhanced. The COV of particle size is positively correlated with the ratio of solute mobile domain $ \beta $ and the dimensionless mass transfer rate $ {\alpha }^{*} $; the goodness-of-fitting of MIM model is better than that of ADE model, and as the COV increases, the fitting global error $ {E}_{\mathrm{i}} $ of ADE model gradually increases. Overall, the COV of particle size controls the size of mobile and immobile domain and solute exchange intensity between two domains, resulting in the non-Fickian behavior of solute transport in porous media. This also causes the error of ADE model gradually increases. MIM model has better applicability for the porous media with larger COV.