Effect of pH on the mobility of the herbicide MCPA in a sand-goethite column: 1D and 2D reactive transport modeling

As a new approach, Positron Emission Tomography (PET) was employed to analyze the flow field, using 18F− as a radiotracer. The observed heterogeneity was reproduced in 2D simulations assuming increased permeability and porosity at the periphery of the column. With this flow model, predicted retardation factors for MCPA were in agreement with the experimental data. Thus, this study demonstrates quantitatively that inconsistencies between static (batch) and dynamic (column) systems can be caused by heterogeneities in fluid flow, i.e., not necessarily by non-equilibrium conditions, which are commonly taken into account. This in turn highlights the need to consider realistic flow fields in studies of contaminant transport in natural matrices.