Contamination of roadside soils by runoff pollutants: A numerical study

Roadway runoff contains multiple pollutant species that can contaminate roadside water, pose risks to aquatic organisms, and cause health problems for human beings. Roadside soils, mostly in their unsaturated states, constitute the first receiving entity for runoff water as the water flows off roadway surfaces. Considering the time-consuming and sophisticated procedures required for experimentally characterizing the soil-water characteristics of unsaturated soils, a finite element analysis (FEA) model was developed in this study and used to predict the contaminating process of variably saturated soils by the pollutants carried in runoff. The governing equation for the transport of multiple pollutant species was formulated based on the mass transport equation for porous media and the Richards' Equation for characterizing variably saturated soils. FEA formulation of the governing equation was accomplished by implementing a linear interpretation function in three-node triangular elements. The FEA model was validated using a miniature laboratory model. The validated FEA model was then implemented to analyze the contamination of a roadside ditch by studying different configurations of soil stratum. The FEA model developed in this work allows the prediction of pollutant distributions in soils at any time of interest, which will greatly facilitate the management of contamination problems caused by roadway runoff. (C) 2014 Elsevier Ltd. All rights reserved.