Fig. 3. Simulated breakthrough results for a two-layered soil column under different layering orders (R1R2 and R2R1). Here R1 is for a nonreactive layer and R2 is for a reactive layer with linear adsorption. Top figure is based on a first-type boundary condition (BC) at the interface between the two soil layers, whereas bottom figure is based on a combined first- and third-type BC.