Numerical modelling of contaminant transport in unsaturated soils

A mass transport model for a multicomponent solution system has been developed which includes coupled pore water, pore air and contaminant transport in unsaturated soils. The approach proposed extends previous modelling work to take account of chemical flow. Equilibrium interaction chemistry is posed independently of the mass transport equations. This leads to a set of algebraic equations to describe the chemical interactions which is coupled to a set of differential equations for mass transport. Competitive sorption among chemical species is simulated by both the constant capacitance model and the triple layer model. A numerical solution of the governing differential equations is achieved via the use of the finite element method as a spatial discretisation technique coupled with a finite difference recurrence relationship to describe transient behaviour.