THE GEOMETRY AND MOTION OF SHARP FRONTS WITHIN GEOCHEMICAL TRANSPORT PROBLEMS

We consider some reactive geochemical transport problems in groundwate r systems. When incoming fluid is in disequilibrium with the mineralog y, sharp transition fronts may develop. We show that this is a generic property for a class of systems where the time scales associated with reaction and diffusion phenomena are much shorter than those associat ed with advective transport. Such multiple timescale problems are rele vant to a variety of processes in natural systems: mathematically, met hods of singular perturbation theory reduce the dimension of the probl ems to be solved locally. Furthermore, we consider how spatial heterog eneous mineralogy can make an impact upon the propagation of sharp geo chemical fronts. We develop an asymptotic approach in which we solve e quations for the evolving geometry of the front and indicate how the n on-smooth perturbations, due to natural heterogeneity of the mineralog y on underlying groundwater flow field, are balanced against the smoot hing effect of diffusion-dispersive processes. Fronts are curvature da mped, and the results here indicate the generic nature of separate fro nt propagation within both model (idealized) and natural (heterogeneou s) geochemical systems.