地下水中VOC挥发因子模型的研究

建立了一个计算地下水中挥发性有机物（VOC）挥发因子的模型.选用半挥发性的1,2,4-三氯苯和挥发性的四氯乙烯为VOC的代表,分别计算了非饱和区土壤为砂土和粘土时的挥发因子.结果表明：蒸发使VOC的挥发因子增大,而下渗则使VOC的挥发因子减小;不论VOC的挥发性强弱,蒸发（下渗）对挥发因子的影响均比较明显;蒸发情况下,非饱和区土壤性质对挥发因子的影响不明显,而下渗情况下,非饱和区土壤性质对挥发因子的影响则趋于明显;此外,当非饱和区土壤为粘土时,VOC的挥发因子受蒸发（下渗）的影响更明显.

ASSESSMENT MODEL FOR VOLATILIZATION BY ORGANIC COMPOUNDS IN GROUNDWATER

The volatilization of VOC from groundwater into ambient air includes three processes: migration in unsaturated zone, 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 mathematical model is developed to calculate the volatilization factor of VOC volatilizing from groundwater 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 groundwater. 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 is relative obvious to both semi-volatile 1,2,4-trichlorobenzene and volatilizable tetrachloroethylene. Under evaporation, the effect of unsaturated zone soil properties on volatilization factor is tiny; but under infiltration, that become more obvious. Furthermore, if the unsaturated zone soil is clay, the variation of volatilization factor of VOC induced by evaporation or infiltration is more significant.