Mechanisms contributing to nonideal transport behavior of contaminants in a naturally heterogeneous aquifer material
AuthorJohnson, Gwynn Rochelle
AdvisorBrusseau, Mark L.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe objective of this study was to investigate the long-term, low-concentration elution tailing of organic contaminants from a naturally heterogeneous (poorly sorted) aquifer material, with a specific focus on characterizing the relative contributions of rate-limited sorption/desorption, physical-heterogeneity-related processes, and rate-limited dissolution of nonaqueous phase liquids. The results obtained for the first component of this three-part study indicate (1) sorption of trichloroethene by the aquifer material was relatively small; (2) sorption/desorption of trichloroethene was found to be nonlinear and rate-limited, contributing to low concentration elution tailing; (3) the overall dispersion associated with the poorly sorted aquifer material was relatively large, also contributing to the tailing observed for the contaminant; and most interestingly, (4) trichloroethene elution curves obtained after significant flushing in the higher-fines aquifer material exhibited greater tailing than those obtained with minimal flushing, suggesting temporal variability of the porous medium dispersive properties. These changes appear to associated with the fines fraction of the aquifer material, and are possibly related to chemical weathering effects. This condition-dependent elution behavior has potentially significant ramifications for evaluating the transport behavior of contaminants in porous media, especially with regard to characterizing the nature and rates of mass-transfer processes. In the second part, the relative contributions of core-scale structuring versus those of rate-limited sorption/desorption to the observed nonideal transport of trichloroethene were examined. The results of these experiments were analyzed using a mathematical model incorporating multiple sources of nonideal transport. The results indicate that both physical and chemical factors, specifically rate-limited diffusive mass transfer associated with nonuniform flow conditions and rate-limited sorption, respectively, contribute to the nonideal trichloroethene transport observed for the undisturbed cores. In the third part, the long-term, low concentration elution behavior associated with dissolution of immiscible-liquid phase trichloroethene was investigated. The complete dissolution of trichloroethene was successfully simulated using a combined, multi process mathematical model. A comparison of these results to those discussed above suggests the low concentration elution tailing observed in the dissolution experiment is associated with rate-limited sorption/desorption. This study clearly indicates that multiple sources of nonideal transport behavior must be considered to fully and accurately characterize contaminant transport in the subsurface.
Degree ProgramGraduate College
Soil, Water and Enviromental Science