Volatilization of a Multicomponent Liquid through Dry Soils: Testing a Model

Abstract

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 the rate of diffusion through a dry soil column of the individual components in a liquid mixture when they are of low or intermediate volatility. We derived equations that relate the vapor pressures of the components to their sorption from the gaseous phase by the soil. We also provided for slow sorption. Three cases of increasing complexity were treated: evaporation of a mixture directly into the atmosphere; evaporation of a mixture through a soil column without significant sorption; and finally, evaporation through a highly sorting soil column, for which a computer program was written. The model has been tested by comparing the evaporation of m‐xylene and n‐dodecane mixtures through sand, and air‐ and oven‐dry Evesham clay soil (Aquic Eutrochrept or orthic grumaquert) in the laboratory. The equilibrium sorption isotherms and sorption kinetics for these soils and compounds were determined in separate 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 hysteresis in the sorption isotherms.

Development of a glass ampoule system for evaluation of long-term sorption/desorption behavior of vapor phase volatile organic compounds in geosorbents

“…Several studies have specifically evaluated vapor phase sorption/desorption behavior of organic compounds in soils and sediments, [5][6][7][8][9][10][11] including the evaluation of the ultimate distribution of VOCs under equilibrium conditions. Such equilibrium information, in the form of equilibrium isotherms, have been derived using a number of methods including soil column systems, 5,6,[12][13][14][15][16][17][18][19][20][21][22] gravimetric systems 8,9,[23][24][25][26][27][28][29] and headspace methods. 7,[30][31][32][33][34] These methods use equilibrium criteria of minutes to hours, 5,12 one day, 7,29,35 or up to a few days.…”

“…7,[30][31][32][33][34] These methods use equilibrium criteria of minutes to hours, 5,12 one day, 7,29,35 or up to a few days. 22,36 Few researchers have reported long-term sorption data (in excess of a few days) with good mass recoveries, even though it has been shown that some organic contaminants may reside in soils up to 19 years 37 or longer. Reinhard and coworkers 18,19 performed long-term isotherm studies using column systems with equilibration periods of the order of months; however Werth and Reinhard 19 reported sorbate mass recoveries of 88% at 15 °C and 60-85% at 60 °C.…”