Study on Volatilization Model of VOC in Vadose Zone

摘要

In health risk assessment on contaminated soil sites by volatile organic compounds (VOC), volatilization exposure is an important part. The volatilization of VOC from vadose-zone soil into ambient air includes three processes: migration in soil column, molecular diffusion in viscous sub-layer, mixing and transportation in ambient air. With analysis of the migration mechanism of VOC in these three processes, a new mathematical model is developed to calculate the volatilization factor of VOC volatilizing from soil into air under evaporation or infiltration. The effect of evaporation or infiltration on volatilization factor can be analyzed with this model, which is helpful to assess health risk caused by the volatilization of VOC in vadose zone. With two representative VOCs of 1,2,4-Trichlorobenzene and Tetrachloroethylene, their volatilization factors are calculated in sandy soil and clayey soil respectively. The results show that the evaporation strengthens volatilization but the infiltration weakens volatilization. The effect of evaporation or infiltration on volatilization of 1,2,4-Trichlorobenzene is more obvious than that of Tetrachloroethylene. Volatilization factors of these two representative VOCs in sandy soil are greater than those in clayey soil under the same evaporation (infiltration) conditions. Furthermore, the variation of volatilization factor of VOC in clayey soil induced by evaporation or infiltration is more significant than that in sandy soil.