Abstract:
The conventional advection-dispersion equation cannot adequately describe all processes driving
solute transport in heterogeneous systems. This dissertation focuses on the individual influences
of both chemical (Chapter 2) and physical processes (Chapters 3 and 4) which affect
solute transport. In Chapter 2 we analyzed uranium transport in natural sediment using the
chemical multirate mass transfer model available within the STAMMT-L software. This model
was used due to many uncertainties of the overall mass transfer influences, which were generalized
into a distribution of first-order rate coeffcients. Results indicated that the multirate
model was adequate for the available experimental data, but the results were not definitive due
to incomplete mass recovery information. A second experimental system was constructed in
order to provide a well-characterized system for analysis. It consisted of 203 low conductivity
(K[subscript im] = 0.011 cm/min) spherical inclusions within a high conductivity (K[subscript m] = 4.66 cm/min) matrix
material, creating a highly heterogeneous binary system with a conductivity ratio of 1/424.
Three flow rates were used to provide complete mass recovery curves. Results were initially
analyzed using a multirate spherical diffusion model available within the STAMMT-L software
(Chapter 3). This worked well for the fast and medium flow rate experiments, while its representation
of the slow flow rate experiment proved inadequate. An analysis of the time scales for
mass transport indicated that the diffusive time through the inclusions was competing with advection
through the matrix as the dominant mass transport mechanism. Subsequent modeling
was performed by direct numerical simulation using the commercially available STAR-CCM+
software (Chapter 4). Results showed inconsistencies with its ability to adequately describe the
system when compared with the multirate model results. This dissertation provides insight into
the importance of gathering complete mass recovery data, obtaining detailed measurements to
describe the system, as well as analysis of results from multirate solute transport processes in
order to obtain an improved understanding of their influences on overall mass transport behavior.
