Abstract

Experimental and modeling studies were performed to investigate the simultaneous transport of trichloroethylene (TCE) and perchloroethylene (PCE) in the vadose zone of a large (25 by 12 by 3 m) well-instrumented artificial aquifer called SCERES. The experimental facility, made up of a 1-m-thick saturated zone and a 2-m-thick unsaturated zone, allowed direct measurements of the contaminants in both the liquid and gas phases. Main objectives of the study were to obtain a better understanding of the fate and transport of chlorinated solvents in the subsurface and, more specifically, to compare simultaneously measured TCE and PCE volatilization rates from the soil surface with predictions obtained with both a comprehensive multiphase multicomponent numerical model (SIMUSCOPP) and a quasianalytical approach based on Fick's first law. The numerical and quasianalytical results generally agreed very well with the observed data. Transient PCE and TCE vapor phase concentrations calculated with the numerical model were found to be close to the observations, which indicated applicability of Raoult's Law. A comparison of observed and calculated TCE and PCE concentrations in the capillary fringe showed more impact of water infiltration on the simulations as compared with the observed data, which may reflect a lack of equilibrium between the gaseous and aqueous phase during leaching for the given experimental flow conditions. A sensitivity analysis showed that the adopted source boundary condition (a fixed nonaqueous phase liquid [NAPL] saturation distribution instead of an injected DNAPL source) did not have much influence on the concentration breakthrough curves, but that temperature can be an important factor influencing the results.

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