Modeling of contaminant transport in soils considering the effects of micro- and macro-heterogeneity

This paper presents development and application of a numerical model for simulation of contaminant transport considering macro- and micro-heterogeneity in soil. Stochastic finite element approach is used to incorporate the effects of the spatial variability of soil hydraulic properties on contaminant fate. The soil micro-heterogeneity effects are modeled with a dual domain concept in which a first order kinetic expression is used to describe the transfer of the solute between the two domains. The model is used to simulate transport of non-reactive solute in a lysimeter under steady-state water flux. Numerical simulation of the problem is carried out for four different scenarios assumed for structure and formation of the soil: a single domain having uniform hydraulic properties (SDU), a dual-domain system with uniform hydraulic properties (DDU), a single domain with spatially variable hydraulic properties (SDV) and a dual-domain system with spatially variable hydraulic properties (DDV). The numerical results are compared with experimental data. The results obtained based on SDU are not in agreement with the measured data. Assuming a dual domain system (DDU) yields satisfactory results but higher accuracy is achieved using DDV scenario. The results show that the combination of the dual domain approach with the stochastic approach improves the numerical predictions. Also, using stochastic finite element approach makes it possible to evaluate variance of concentration as an index of reliability of the result.