Upward Transport of Trichloroethylene Vapour in a Dry Soil Column

Abstract

Experimental and modelling studies were performed to assess the predictability of gas phase transport models based on the Fickian-type diffusion expression and dusty-gas model (DGM) equations for the upward transport of trichloroethylene (TCE) vapour at low vapour source densities in a dry soil column. The TCE vapour concentrations measured upstream in the column were only 6% and 15.7% of the TCE saturated vapour concentration (i.e., TCE vapour densities of 0.031 and 0.08 g/L, respectively) when TCE liquid existed in the upstream cavity as a vapour source. A good fit between the model-predicted profile of the downstream TCE vapour concentration and the observed data can only be attained by using a tortuosity value that is 0.2–0.3 times of that computed by the Millington and Quirk’s (1961) empirical equation. This result revealed that diffusion dominates over advection for the aforementioned transport conditions. Furthermore, the differences between the concentration evolution profiles away from the source predicted by the Fickian and DGM-based models present a reverse trend depending on whether the downstream boundary is covered (impermeable) or uncovered (opened to the air). The results revealed that the predicted upward transport of dense vapour at low source densities with a covered downstream boundary predicted by the two models differed considerably. • Trichloroethylene (TCE) vapour was <20% saturated in the experimental soil column containing the TCE liquid. • The fitted effective molecular diffusion coefficient was less than the estimated coefficient by the usual method. • A Fickian-type diffusion model may under- or over-predict vapour concentrations for upward transport of dense vapour.