Solute Transport Through Small and Large Unsaturated Soil Columnsa

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Abstract
Unsaturated solute transport experiments were conducted using several small and one large column packed with the same sandy soil material.Chloride and tritium were used as tracers for water movement. Soil solution samples were collected as a function of time in the small columns and versus time and depth in the large column. The data were compared with solutions of the classical two‐parameter convection‐dispersion equation and also with solutions of a more elaborate four‐ parameter transport model that assumes a fraction of the water to be immobile. Fairly symmetrical effluent curves resulted from both the small and large columns, suggesting small transfer coefficients between mobile and immobile regions and small amounts of immobile water. Dispersivity values ranged from 1 cm for the small columns to about 5 cm for the 6‐m‐long column; retardation factors for chloride were nearly the same (about 0.8) for both column sizes. Thus, while the dispersivity measured in the small columns did not apply to the large columns, the same retardation factors could be applied to the different scale columns.