The University of Arizona - Contaminant Transport Group

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Areas of Study


Organic Liquids and Multi-phase Systems

Generally, the most critical issue for hazardous waste sites contaminated by organic compounds is whether or not immiscible-liquid phases are present in the subsurface. Immiscible liquids trapped in the subsurface serve as long-term sources of contamination, and their presence can greatly impact the costs and time required for site remediation. We are investigating the behavior of organic immiscible liquids such as chlorinated solvents, and their impact on site characterization and remediation. Our research encompasses the pore scale, column scale, intermediate scale, and field scale.

Contaminant Transport Processes

The transport and fate behavior of contaminants mediates the risk posed by a site, as well as the viability and effectiveness of remediation efforts. We are interested in the underlying processes, such as sorption, diffusion, and transformation that influence transport and fate of reactive contaminants. We are also interested in the impact of geochemical and physical heterogeneity of porous media on transport and fate. We are investigating the transport and fate behavior of a wide variety of contaminants, including organic compounds, heavy metals, colloids and nanoparticles, and pathogenic microorganisms.

Mathematical modeling has become an indispensable tool for investigating contaminant transport and fate. Two primary uses for mathematical models are investigation of fundamental processes and site-specific management applications. Regarding the former, mathematical models are a powerful means by which to integrate process-based information for complex systems, and thus are a key method for investigating phenomena over a wide range of conditions that are problematic to investigate by other means. We are involved in the development and application of advanced mathematical models for simulating the transport of reactive contaminants in heterogeneous porous media.

Regarding the second use, mathematical modeling has become a critical component of risk assessment, characterization, and remediation-system development efforts for hazardous-waste sites. Unfortunately the use of advanced, multiprocess mathematical models for such applications is often greatly constrained by insufficient knowledge of subsurface properties and contaminant distributions. This is particularly the case for immiscible-liquid contaminated sites, for which the location and architecture of the sources zones is rarely known in detail. Thus, it is often necessary to use simpler models (e.g., lumped-process models) for simulating transport at the field scale. A critical issue associated with the use of simpler models is how to translate mechanistic information (e.g., pore-scale and local-scale processes) to the simplified models. This is often referred to as the “upscaling” issue. We are examining this issue and the use of simplified models for example for simulating mass transfer and transport for organic-liquid contaminated systems.

We are investigating issues associated with remediation of subsurface environments at hazardous waste sites. One area of focus has been remediation of source zones. For example, we have conducted several studies to evaluate the use of reagents (e.g., surfactants, cosolvents, cyclodextrins) for enhancing the removal of organic-liquid contamination from source zones. A major effort has been focused on examining the efficacy of cyclodextrin as an alternative to surfactants and alcohols as a solubilization-enhancement agent for source-zone remediation. In addition, we have examined the use of cyclodextrin for remediation of mixed wastes (organic-liquid and metals). This research has spanned laboratory batch-reactor experiments to field studies. We have also conducted batch-reactor, flow-cell, and pilot-scale field studies on the use of in-situ chemical oxidation (using potassium permanganate and fenton’s reagent) for remediation of chlorinated-solvent contaminated source zones. An area of current focus is the impact of the mass reduction associated with source-zone remediation efforts on the aqueous-phase mass flux.

Another area of focus is on management of sites that have large groundwater contaminant plumes. Large dissolved-phase groundwater contaminant plumes often form at chlorinated-solvent contaminated sites because chlorinated solvents typically have relatively high solubilities (in comparison to maximum contaminant levels), limited retardation, and generally low transformation potential. In many cases, the plumes are hundreds of meters to several kilometers long. For many sites, a large fraction of the contaminant mass comprising the plume may reside within laterally extensive lower-permeability units adjacent to the aquifer. The mass in such domains is poorly accessible to flowing groundwater, and thus is not amenable to removal via hydraulic displacement methods (e.g., pump and treat). As a result, this mass serves as a long-term contaminant source via diffusive mass transfer back into the flowing groundwater domain (so-called “back diffusion”). This process is critical to long-term management and ultimate closure of chlorinated-solvent contaminated sites.

We have been involved in the development, testing, and application of numerous innovative tracer-test technologies. These include the partitioning tracer test for measuring immiscible-liquid contamination, the partitioning tracer test for measuring water content, the interfacial partitioning tracer test for measuring fluid-fluid interfacial area, the multiple-solute tracer test for characterizing diffusive mass-transfer processes, and the biotransformation tracer test. We are also interested in the development and application of other characterization methods, such as compound-specific stable isotope analysis and mass-flux characterization.

Groundwater Quality Assessment and Environmental Research Translation


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