Two Dimensional Numerical Simulation of Groundwater Contamination in the Highway Environment

There are many factors that affect the groundwater contamination in the highway environment. This paper reports a 2-dimensional numerical simulation of the movement of contamination with water into the sub-grade and water table beneath a road to determine the major factors affecting transport of contaminants. The modelling parameters were assembled from various literature sources and 8 scenarios were adopted to simulate the possible controlling conditions. Analyses were undertaken to simulate 2 to 4 years of water percolation through the pavement sub-structure, some contamination arriving at an underlying ground water table and other arriving at a lateral drain. Overall, the potential for ground water table contamination above probable limit values is very low except in extreme permeability and low sorption cases. Results show, firstly, that the sorption capacity of aggregates should be taken into account, especially as the run-off is likely to be a more important consideration than the possibility of leaching from the pavement’s construction layers. Secondly they show that the permeability of sub-grade soil, the suction-water content characteristics and the partitioning coefficient are the major factors affecting the degree of groundwater contamination in the highway environment. Of these, the sorptive capacity appears to be the key issue. Thirdly, it is shown that the rainfall pattern has little effect if the quantity of rainfall is the same.