The dispersive transport of solutes in soils is described by diffusive equations and by models that assume the existence of a causal relationship between physical characterisitcs of porous media, its water content and the macroscopic manifestation of processes that take place in it. The validity of this proposition, as a criterion in the formulation of process models that govern the transport of solutes in soils, is discussed heuristically. Based on indicators derived from a moment analysis of breakthrough curves (BTCs), it is possible to objectively evaluate the link that the system's characteristics establish with relation to the local equilibrium assumption and therefore with success or not in adopting a modeling approach. As a result, non-ideal BTCs are no more than the macroscopic manifestation of an incomplete process, and the attainment of a symmetric, Gaussian distribution of solute concentration can only be guaranteed with the adoption of a "minimum transport length".
dispersive transport; structured soils; modeling