Contaminant transport in porous media in the presence of colloids: Numerical and experimental investigations

Contaminant transport in the presence of colloids is numerically and experimentally studied. The numerical component is used to develop a two-dimensional, finite difference model having a total variance diminishing scheme. The model is first used in homogeneous domains to evaluate sensitivity in contaminant migration rates as compared to reactive transport parameters governing colloid-associated transport problems. The model is also used to evaluate the hypothesis that colloids can retard contaminant movement. It is found that colloids can increase the effective retardation factor for a contaminant under certain combinations of reaction rates and coefficients.; The model is used to study colloid-facilitated transport under heterogeneous conditions and to evaluate impacts of physical and geochemical heterogeneities and their correlations on contaminant transport. The effect of heterogeneity is investigated under a stochastic framework using Monte Carlo simulations. The results show that colloids reduce the uncertainty range in contaminant arrival times as compared to contaminant transport in the absence of colloids. In addition, the effect of geochemical heterogeneity is found to be important only if it is correlated to the physical heterogeneity.; The final portion of the numerical investigations aims at developing an efficient method to study kinetics of nonlinear reactions among colloids, contaminants, and porous media. The finite-cell method is adapted and extended to investigate the effects of various sorption isotherms including linear, Freundlich, and Langmuir. Results indicate that the effect of colloids on nonlinearly sorbing contaminants is altered from facilitation to retardation depending on the Freundlich exponent and concentration value.; The experimental component of the study focuses on characterizing the chemical conditions where colloids act as movement-retarding agents and yield a larger effective retardation factor. In addition, the experimental work is used to verify the developed model and apply it to realistic conditions. Experimental data confirm the role of colloids as retarding agents. The results of the verification show that the model functions properly and reasonably describes the interactions among colloids, contaminant, and solid matrix. Additionally, the model can be used to predict transport of contaminant in the presence of colloids.