Liquid interactions with porous media and the fate of toxic materials

Abstract

Toxic liquid chemicals released into the environment may pose an imme- diate risk to human health through contact or related vapour hazards. However, they can also interact with surfaces and remain in situ, poten- tially presenting a subsequent hazard. To improve understanding of the fate of these materials in different environments, the study group inves- tigated interactions between liquid droplets and porous media across a range of different time scales.
Splashing and the subsequent re-entrainment of micro-droplets into the atmosphere was identified as one possible mechanism though which the area effect of a contamination could be significantly increased. The study group looked at experimentally determined splashing thresholds for droplet impacts with impermeable substrates, to determine initial predictions of whether or not a given droplet will splash. In cases where splashing occurs the droplet inertia is the most significant effect driving the initial phase of the liquid infiltration into a porous media and the study group developed a model to investigate this behaviour.
For longer time scales the study group determined that capillary suction played the most significant role in spreading the liquid within the porous medium. Models for the evolution of the partial saturation within a porous medium based on Richards’ equation were investigated. Over even longer time scales evaporation converts the liquid back into a po- tentially hazardous vapour. The study group started to incorporate evaporation into models of liquid infiltration in a porous medium in order to describe this phenomenon. Recommendations for future theo- retical, numerical and experimental modelling are also provided.