EXPERIMENTS AND MODELING OF THE TRANSPORT OF TRICHLOROETHENE VAPOR INUNSATURATED AQUIFER MATERIAL

A bench-scale reactor system was used to investigate mass-transfer dyn amics and transport of trichloroethene (TCE) vapor in a column of unsa turated aquifer material under conditions of advective gas flow, at 25 degrees C and 90% relative humidity. Two gas flows (40 and 80 mL/min) and two relative vapor pressures of TCE (10% and 90% P/P-o,P- where P is vapor pressure and P-o is the saturation vapor pressure) were sele cted as experimental variables. Breakthrough curves were generated for week-long inputs of TCE-laden air and for short pulses of a nonsorbin g tracer gas. Equilibrium sorption isotherms for TCE were also measure d and used as tools far interpreting the column experiment results. Sl ow mass-transfer kinetics were observed in all of the transport experi ments. Evidence from the breakthrough curves and the sorption isotherm s suggested that, at 90% P/P-o, a significant amount of TCE was conden sed in pores or sorbed at the gas-water interface. Desorption and vola tilization of interfacially sorbed TCE appeared to be rapid processes. The applicability of a recently developed mathematical transport mode l using a statistical gamma distribution of desorption rate constants was tested using the experimental data. The gamma distribution provide s two adjustable parameters to account for sorption site heterogeneity and multiple mechanisms of sorption. When fit to the breakthrough cur ve obtained at high flow and high relative pressure, the model success fully predicted TCE frontal breakthrough and elution profiles at all o ther experimental conditions with no adjustable parameters. The predic tive capability of the gamma model was shown to be superior to that of two commonly used alternative model paradigms: the two-site first-ord er and two-site spherical diffusion models.