To predict the transport of volatile organic chemicals(VOCs), several models - unsaturated flow model(USF), equilibrium distribution model (EDIS) and distribution and transport model(DAT)-are developed, and various kinds of experiment have been carried out to validate these models.
As a spilled pollutant can b□□vectively moved by rainfall, the precise estimation of water content change with time and depth in the soil profile is necessary, and water content profile from the USF model are compared with the experimental result. The hydraulic conductivity and water content relationship of Brooks and Corey [1964] is applied to the USF model, and the measurement for capillary and water content relatioship has been conducted using a developed apparatus.
The partition coefficients of VOCs are experimentally obtained by the headspace analysis. Furthermore the distribution of pollutants mass with time and depth is measured by a set of small column series, and are compared with the result of EDIS model.
The leaching flux at the bottom and the volatilizing flux at the surface of soil in large column are measured to simulate the fluxes emitting from the boundaries of vadoze zone to the atmosphere and to the aquifer. Cumulative masses emitted to the atmosphere and to the aquifer during experimental period, and the remaining mass in a column packed with the soil media are also investigated for the mass balance check.
Selected pollutants for this study are 1,1,1-trichloroethane (TCA) and dichloromethane(DCM). They are the widespreadly used VOCs in the manufacturing processes, and can be sufficiently the representative priority organic pollutant of nonbiodegradable, volatile, and toxic solvents. And the adopted soil media are sandy soil and silt-clay mixture that has different content of soil organic carbon.
