Upward Transport of Trichloroethylene Vapour in a Dry Soil Column
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Upward Transport of Trichloroethylene Vapour in a Dry Soil Column Chiu-Shia Fen 1
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& Chiwei Tsoa & Poyang Yen
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Received: 8 January 2020 / Accepted: 16 November 2020/ # Springer Nature Switzerland AG 2020
Abstract Experimental and modelling studies were performed to assess the predictability
of gas phase transport models based on the Fickian-type diffusion expression and dustygas 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 modelpredicted 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. Highlights
• Trichloroethylene (TCE) vapour was 0.28 g/L) have been observed in these studies. For VI problems, the indoor hazardous vapour/gas concentration is typically estimated by assessing soil gas concentrations sampled at certain depths from the ground surface and near the building of interest. Wang et al. (2019, 2020) conducted experiments on upward and lateral TCE vapour diffusion from a vapour source at densities from 0.02 to 0.04 g/L in a twodimensional sand tank to assess vertical and lateral vapour concentration attenuation in unsaturated soils. They compared the soil gas concentration of TCE measured at various locations on the sand tank with the predictions obtained from Fickian-based models (only diffusion is considered) and concluded that the vapour concentration tends to decay linearly with the vertical diffusion distance. Furthermore, they investigated a partially covered system (impermeable films covering some parts of the tank surface), which was representative of impermeable pavements in some parts of ground surface. The results of their experiment
Upward Transport of Trichloroethylene Vapour in a Dry Soil Column
confirmed that soil surface covers alter the distribution of the vapour concentration and increases their concentration beneath the covers. Because the pressure variations induced by vapour transport and gravitational force affect vertical transport, both advection and diffusion should be considered in dense vapour
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