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THE INTERPLAY BETWEEN GEOCHEMICAL REACTIONS AND ADVECTION-DISPERSION IN CONTAMINANT TRANSPORT AT A URANIUM MILL TAILINGS SITE
Zhu, C. AND D S. Burden*. THE INTERPLAY BETWEEN GEOCHEMICAL REACTIONS AND ADVECTION-DISPERSION IN CONTAMINANT TRANSPORT AT A URANIUM MILL TAILINGS SITE. Presented at AGU 2000 Spring Meeting, Washington, DC, May 30 - June 3, 2000.
It is well known that the fate and transport of contaminants in the subsurface are controlled by complex processes including advection, dispersion-diffusion, and chemical reactions. However, the interplay between the physical transport processes and chemical reactions, and their relevant importance in determining contaminant fate and transport has not been intensely explored due to the complexity of the problem. Numerical models that couple the physical transport processes and various types of chemical reactions, provide a new tool to decipher the intricacy of the interplay. This study used such a model, PHREEQC (Parkhurst and Appello, 1999), to simulate the advection-dispersion, aqueous speciation, precipitation-dissolution, and surface adsorption reactions in a contaminated aquifer beneath a uranium mill tailings pond in the western USA. An abundant amount of field data has been collected from this site (Zhu, Anderson, and Burden, 1999, submitted to Ground Water), which was to construct a one-dimensional model. The modeling results unravel a complex history of interplay of different processes. In different time-space domains, physical and chemical processes alternatively control the transport of reactive constituents. For example, sulfate transport is controlled first by advection-dispersion, then precipitation of gypsum at the calcite dissolution front, followed by dissolution, when uncontaminated upgradient ground water flushes the aquifer, and finally surface reactions, after all the gypsum in the aquifer is dissolved. These results illustrate that our understanding of contaminant fate and transport can only be achieved when multiple, coupled processes are considered simultaneously.
Record Details:Record Type: DOCUMENT (PRESENTATION/ABSTRACT)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
SUBSURFACE PROTECTION AND REMEDIATION DIVISION
TECHNICAL ASSISTANCE AND TECHNOLOGY TRANSFER BRANCH