Predicted retardations of concentration fronts using a mass-balance approach

Regardless of the chemical controls for a pollutant on sediment sorption or release from an immiscible organic liquid, a simple mass balance can be used to predict the retardation of the ground water pollutant front moving downstream from a source of constant composition. The retardation is the ratio of the total molar difference of pollutant across the front to the molar difference in ground water. The mass-balance approach presented here uses a flushing factor for the entire front. It is implicit in the commonly used retardation factor for pollutants undergoing linear sorption, but does not appear to have been used to predict retardation of concentration fronts involving nonlinear sorption or partitioning in hydrochemical studies. Yet the computations require only limited experimental or field data or the use of an algorithm describing sorption or partitioning of the pollutant. Close agreement was obtained between retardations predicted using the mass-balance approach and those reported from numerical modeling and column experiments in the literature.