Dispersion in Soil Columns: The Snow Plow Effect

Miscible displacement and tracer techniques were utilized to study the exchange and transport of cations in a column of soil with a low cation exchange capacity. The specific case studied was one in which an unlabeled CaCl 2 solution was at least 10 times greater than that of the initially labeled Ca present in the soil solution and on the exchange. Most of the exchange was observed to take place at the front of the in coming solution, resulting in a labeled solute concentration at one pore volume of the breakthrough curve that is much greater than the initial concentration of the labeled soil solution and complete removal of initially adsorbed ions in two pore volumes. A theoretical approximation is developed which predicts the phenomenon adequately.