ABSTRACT
We like to address now how we can predict the fate of chemicals that leach from waste sites and appear to vanish in the invisible subsurface environment. We use numerical models since the combination of transport and chemistry often yields complicated concentration patterns which are difficult or impossible to calculate otherwise. Numerical solutions of the advection-reaction-dispersion (ARD) equation are approximative and may be incorrect if certain stability criteria are violated. These criteria are explained with 1D examples that illustrate how to calculate diffusion of seawater and advective flow in laboratory columns. They also apply in multidimensional models.
