VOLATILIZATION OF A MULTICOMPONENT LIQUID THROUGH DRY SOILS - TESTINGA MODEL

Spilled or leaked petroleum products often contaminate groundwater and subsequently evaporate through the soil to the atmosphere by gaseous diffusion. This study developed and tested a model that can predict th e rate of diffusion through a dry soil column of the individual compon ents in a liquid mixture when they are of low or intermediate volatili ty. We derived equations that relate the vapor pressures of the compon ents to their sorption from the gaseous phase by the soil. We also pro vided for slow sorption. Three cases of increasing complexity were tre ated: evaporation of a mixture directly into the atmosphere; evaporati on of a mixture through a soil column without significant sorption; an d finally, evaporation through a highly sorbing soil column, for which a computer program was written. The model has been tested by comparin g the evaporation of m-xylene and n-dodecane mixtures through sand, an d air- and oven-dry Evesham clay soil (Aquic Eutrochrept or orthic gru maquert) in the laboratory. The equilibrium sorption isotherms and sor ption kinetics for these soils and compounds were determined in separa te experiments, and other parameters were obtained from the literature , so that the model contained no adjustable fitting parameters. There was fair agreement between the model predictions and the experimental results. Discrepancies were attributed to errors in chemical analysis and the boundary effects that arose from rather short columns, and to the assumptions that the compounds did not compete for sorption sites on the soil, that Raoult's Law was obeyed, and that there was no hyste resis in the sorption isotherms.