Fast Prediction of Runoff Removal of Chemical Pollutants Uniformly Dispersed in a Drainage Basin

Abstract

A simple model is described for the prediction of the solid→solution transfer of chemical pollutants uniformly dispersed in a drainage basin. The model is based on our recent finding that the mean residence time of such a contaminant is simply proportional to its dimensionless solid/solution distribution coefficient. The proportionality constant is independent of the nature of the chemical and can be assigned a value using a constant flux, naturally occurring radionuclide. Since the model assumes that the removal primarily occurs in the solution phase, it is important to include runoff removal constant in model expressions. A parameter describing downward leaching of chemicals is also included. This is especially important for chemicals with low distribution coefficients. The model is evaluated for the Ottawa River drainage basin using a conservative (⁹⁰Sr) and a particle-reactive (¹³⁷Cs) fallout radionuclide the measured long-term (~ 20 yr) terrestrial fluxes of which compare favourably with those inferred from the model. The observed variance between the two values for few years is noted and discussed.