Environmental conditions affecting organic vapor advection and diffusion fluxes from the unsaturated zone to the atmosphere under natural conditions.

摘要

Natural attenuation has been actively studied and often selected as a final clean-up process in remediation of contaminated ground-water and soil in the US for the last decade. Accordingly, understanding of natural processes affecting the fate and transport of contaminants in the subsurface becomes important for a success of implementation of the natural remediation strategy. The natural processes occurring in the unsaturated zone affect movement of contaminants from the source area into the atmosphere or groundwater. Contaminant advection and diffusion processes in the unsaturated zone are naturally related to environmental changes in the atmosphere. The atmospheric pressure and temperature changes, and infiltration affecting the transport of contaminants in the subsurface are investigated in this dissertation.; Moisture content, trichloroethylene (TCE) concentration, temperature, and pressure variations in the subsurface were measured for the July, August, November, and December 2001 at Picatinny Arsenal, New Jersey. These data were used for a one-phase flow and one-component transport model in simulating the soil-gas flow and accordingly the TCE transport in the subsurface in accordance with the atmospheric pressure variations at the surface. The soil-gas velocities during the sampling periods varied with a magnitude of 10-6 to 10-7 m s-1 at land surface. The TCE advection fluxes at land surface were several orders of magnitude smaller than the TCE diffusion fluxes. A sensitivity analysis indicated that advection fluxes were more sensitive to changes in geo-environmental conditions compared to diffusion fluxes. Of all the parameters investigated in this study, moisture content has the most significant effect on TCE advection and diffusion fluxes. Daily water-table fluctuations with an amplitude of 0.1 m induce advection fluxes as big as barometric pumping. The investigation of effect of atmospheric pressure and temperature changes, and infiltration on TCE transport in the subsurface with a two-phase flow, heat transfer, and contaminant transport model shows that the atmospheric pressure variations are considered to be a major factor in inducing soil-gas flow and accordingly advection transport in the subsurface under natural conditions.