AuthorPopovicova, Jarmila, 1968-
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PublisherThe University of Arizona.
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AbstractThe goal of this dissertation was to examine transport of gas-phase contaminants and the processes causing nonideal transport. With one exception, all experimental work was performed with synthetic porous media (glass beads). I performed experiments with methane, trichloroethene, benzene, and toluene. Transport experiments for gas-phase contaminants in dry homogeneous and heterogeneous porous media were performed to study dispersion of gases during transport. Axial diffusion was found to be a primary contributor to dispersion at gas velocities < 20 cm min⁻¹. Conversely, mechanical mixing was the main contributor to total dispersion at gas velocities > 50 cm min⁻¹. Dispersion of gas-phase contaminants during transport through dry heterogeneous (macroporous) medium was caused by three processes: axial diffusion, which was predominant at gas velocity < 20 cm min⁻¹ and negligible at gas velocity > 100 cm min⁻¹; mechanical mixing, predominant at gas velocities ranging from 30 to 120 cm min⁻¹; and diffusion between macropore and micropore domains, the main contribution to total dispersion at gas velocities above 160 cm min⁻¹. The latter process was responsible for rate-limited transport of gas-phase contaminants (methane, trichloroethene, benzene) through heterogeneous porous medium causing increased dispersion, early breakthrough, and tailing of breakthrough curves. Transport of gas-phase contaminants through the unsaturated heterogeneous porous medium showed a similar trends. The presence of heterogeneity and immobile water caused nonequilibrium transport of methane and trichloroethene. Predictions of breakthrough curves, which fit the experimental data well, were estimated independently and demonstrated that diffusion between macropore and micropore domains have a more pronounced effect on transport nonequilibrium than diffusion in immobile water. Retention of gas-phase contaminants in the unsaturated porous media was also examined. Solid-phase sorption of gas-phase contaminants was minimal and thus not responsible for delay during the transport. The major contribution to total retention was due to accumulation at the gas-water interface. For example, 62-73% and 30-50% total trichloroethene mass was retained at the interface during transport through the glass beads and aquifer material, respectively. Accumulation of benzene at the interface contributed to total benzene retention by 53-61% of total mass.
Degree ProgramGraduate College
Soil, Water and Environmental Science