Transport and Fate of Contaminants in Groundwater
The following is a list of currently active externally funded research projects:

Analysis of Halogenated Organic Particle-Scale Desorption via Column Studies and C-13 Solid State NMR Spectroscopy - Reinhard, M. (EPA)
Research has shown that a significant fraction of organics sorbed to soils and sediments (geosorbents) resists desorption. This fraction is not amenable to conventional treatment and needs special consideration in fate and transport assessment. In this project we identify sorbent properties that govern slow desorption and compare results of desorption studies with predictions based on mechanistic models. The approach is to artificially contaminate geosorbents with TCE, deuterated TCE and/or PCE either individually or as mixtures and to quantify rate of desorption as a function of initial sorbent loading and desorption conditions. Data suggest that the sorption sites of the slow desorbing fraction reside in micropores and that diffusion of is sterically hindered.

Field-Testing of Palladium-Catalyzed Hydrogenation for Chlorinated Hydrocarbon Removal - Reinhard, M. and Roberts, P.
This project aims to evaluate palladium catalyzed hydrodehalogenation using hydrogen gas as a method for removing halogenated hydrocarbon compounds form contaminated water. Preliminary studies indicate that hydrodehalogenation proceeds under mild conditions when facilitated by a palladium catalyst. The project goal is to gain operational experience with the H2/Pd process under field conditions. Specifically we aim to: 1) quantify catalyst efficacy; 2) identify and minimize the factors contributing to catalyst fouling; 3) measure competing reactions and determine their hydrogen consumption; 4) evaluate the need for pretreatment; and 5) determine how best to supply hydrogen safely and economically. Results will be used to optimize the process, provide design criteria, and evaluate cost effectiveness compared with alternative treatment methods.

The Fate and Transport of Wastewater Indicator Compounds During Groundwater Recharge with Water of Wastewater Origin - Reinhard, M. (Orange County Water District).
In many water-short areas treated effluents are often the only alternative to augment existing water supplies. Increasingly, effluents are treated so that they can be percolated into the ground to augmented depleted aquifers. This project aims to assess the microbial, chemical and physical processes that affect the fate and transport of anthropogenic contaminants during water percolation and groundwater transport. The data will be useful for developing models that predict the water quality of recharge water as a function of source water quality, soil type, residence time in the ground, and travel distance. Such models will serve to develop science-based regulations for artificial water reuse operations.

Diffusional Rate Limitations in Heterogeneous Porous Media: Model Structure, Scale, and Geologic Characterization - Freyberg, D.L. and P.V. Roberts (EPA)
This recently completed project focuses on elucidating the nature and environmental significance of both physico-chemical and apparent diffusional rate limitations during solute transport in saturated, heterogeneous porous media, with a view to evaluating the role of diffusional limitations in contaminant remediation. The research considers the relative importance of diffusion and slow advection manifested over a range of spatial scales, from the grain scale up to regional scales, within the context of analytical and numerical transport models that account for advection, diffusion, dispersion, and sorption.

Strategies for Maintaining Open Water in a Rapidly Sedimenting, Small Reservoir - Cohen, P.S. and D.L. Freyberg (Packard Foundation)
Searsville Lake is a small reservoir on Stanford's Jasper Ridge Biological Preserve which is rapidly filling with sediments from the Corte Madera Creek watershed. The reservoir provides important avian habitat and is used actively in both research and teaching at the Preserve. This project is exploring opportunities to manage the sediment flux tthrough Searsville Lake so that a modest amount of open water can be maintained in the reservoir.

Assessing the Water Balance for Large Ephemeral Streams in Arid Environments - Freyberg, D.L. (USGS student support)
Ephemeral channels in arid and semi-arid environments are an extremely important hydrologically and ecologically. Flow in ephemeral channels is complex, involving short, rapidly rising and falling hydrographs, significant sediment and debris transport, and nearly complete infiltration of the flow over a channel reach. Closely coordinated with an ongoing USGS field data collection project, this dissertation research couples field data with numberical modeling in an attempt to better characterize and predict groundwater recharge from ephemeral channels.

Engineering Pedagogy--Teaching Turbulent Diffusion in Engineering Fluid Mechanics - Freyberg, D.L. and J.R. Koseff (NSF student support)
This doctoral research project focuses on the pedagogy of engineering fluid mechanics, in particular, teaching and learning the concept of turbulent diffusion. Closely coupled with laboratory research studying the role of turbulent diffusion in the foraging behavior of lobsters, this doctoral project is using advances in science education, cognitive science, and psychology, along with carefully designed experimentation and testing, to develop effective teaching techniques for a key, difficult concept in fluid mechanics.

Characterization and Modeling of Sorption Processes for the Nevada Nuclear Waste Storage Investigations - Leckie, J. O. (Los Alamos National Laboratories)
The objectives of this research is to investigate the adsorbtive behavior of the uranyl and neptunyl ions in aqueous systems continuing goethite, hematite and, possibly, feldspars. These studies will include experimental work with competing ligands (e.g., carbonate, EDTA, natural humics) as well as studies to investigate competitive behavior with calcium and magnesium. The resulting data will be modeled using surface complexation models.

Radionuclide Speciation in Heterogeneous Aqueous Geochemical Environment - Leckie, J. O. (Sandia National Laboratory)
This project is concerned with experimental and theoretical studies of the interaction of radionuclides with mineral/solution interfaces likely to be found in the WIPP site high level waste repository. The experimental part involves both time dependent and equilibrium studies of neptunyl and uranyl ion interactions with clays and hydrous iron oxides over a range of ionic strengths (1 x 10-3M - 3M) and in the presence of competing ligands. The theoretical aspects are concerned with the development of modeling approaches for adsorbate interactions with clay surfaces.

Particle-Particle Interactions in Marine Systems: Steady-State, Continuous Flow, Aggregation Studies - Leckie, J. O. (NSF)
Four linked objectives highlight this proposed study of aggregation/sedimentation dynamics. First, a new type of laboratory apparatus will be developed to allow previously unachieved simulation of a continuous flow, steady state system. The simulation apparatus is designed for study of real time aggregation from the simplest processes to relatively complex, biologically mediated processes in controlled, reproducible conditions. Second, two innovative particle size measuring technologies are proposed which allow noninterfering observation of aggregation/sedimentation dynamics. Development and adaptation of these techniques aims at avoiding the sampling artifacts, limited size range and restrictive fluid and particle requirements inherent in many traditional measuring techniques (i.e., electrozone, settling rate). Third, an experimental sequence is suggested which uses controlled variations of particle type, surface chemistry and fluid conditions to assess the interplay of physical, chemical and rudimentary biological factors that have been scantly addressed by previous research. Particular effort is devoted to elucidating both the unique and interactive mechanisms by which exopolymers from selected marine organisms enhance or retard aggregation. Fourth, laboratory findings will be modeled to provide a usable tool for future predictive, design, and analytical work.

Pore-Scale Hydrodynamics and Physicochemical Transport. Constitutive Relations of Solute Transport and Transformation at the Darcy Scale - Kitanidis, P. K. (WRHSRC, NSF, DuPont)
In terms of physico-chemical fundamentals, the transport and transformation of reactive solutes is most satisfactorily understood and quantified at the pore scale. However, this scale is too microscopic for almost all practical applications. In practice, the smallest scale for modeling the transport and chemical fate of solutes in porous media is the laboratory or Darcy scale, which is much larger than the pore scale. At the Darcy scale, a complex medium that actually consists of pores, a solid matrix with biofilm, etc., is replaced by a homogenized medium characterized by constitutive relations among macroscopic variables and parameters. The general advection-dispersion-reaction equation, which is the starting point of every practical modeling effort, is based on these relations and parameters and purports to describe the transport behavior of a concentration spatially averaged over a block of the order of at least centimeters. What is the appropriate form of this equation and what parameters should be used? This research aims at providing answers to these questions. The methodology followed is to model flow, transport, and chemical transformations at the pore scale and then to scale up in order to derive constitutive equations and parameters. The constitutive equations and parameters to be obtained will thus be consistent with the fundamental physico-chemical principles as well as the heterogeneity of the medium. The longer-term objective is to promote a firmer understanding of the factors that control the transport and chemical fate of pollutants, substrates, and electron acceptors at the Darcy scale.

Factors Controlling Solute Dilution in Heterogeneous Formations - Kitanidis, P. K. (NSF, SGF)
Although the effect of heterogeneity on the spreading of contaminant plumes has been studied, the effect of heterogeneity on dilution remains to be determined, especially at "early" times relevant in tracer tests and remediation projects. Dilution is measured by the peak concentration and the volume occupied by solute. Spreading is quantified by the spatial second moment of the concentration distribution. In assessing environmental impacts of groundwater contamination, it is important to be able to anticipate peak concentrations, not just the spatial extent of contamination. We conduct theoretical analysis, detailed numerical simulations, and comparisons with field data. Contaminant dilution measures are related to the porous media constitutive parameters and, primarily, the variability of hydraulic conductivity and the local dispersion. Predictions of dilution are made via analytical approximations, which lead to predictive partial differential equations. The approximations validity is assessed through numerical simulations and the results are evaluated by comparison with results from field experiments. Objectives: (a) a better understanding of the time-evolution of contaminant concentration levels, and (b) guidelines to the practitioner for assessing dilution of contaminants in heterogeneous geologic formations.

Use of In-situ Bioaugmentation for Remediation of an Aquifer Contaminated with Carbon Tetrachloride - Phase III - Criddle, C.S. (Michigan Department of Environmental Quality)
This project involves full-scale demonstration of bioaugmentation for remediation of a site contaminated with carbon tetrachloride. Among the many issues explored are factors affecting transport and competitiveness of a non-native microorganism, carbon tetrachloride degradation, denitrification, chemical delivery, and the role of subsurface heterogeneity.

In Situ Stabilization of Persistent Organic Contaminants in Marine Sediments - Luthy, R.G., U. Ghosh, R.N. Zare and collaborators at the US Army Engineer Research and Development Center, Vicksburg, MS and the University of Notre Dame (US Department of Defense, Strategic Environmental Research and Development Program) The addition of coal-derived sorbents is being evaluated as a treatment technology to reduce the bioavailability and toxicity of polychlorinated biphenyls [PCBs] and polycyclic aromatic hydrocarbons [PAHs] in sediments. This work comprises a suite of tests with contaminated sediment from Hunters Point Naval Shipyard, San Francisco Bay.  

Contaminated Sediment Processes and Bioavailability - Luthy, R.G., S.G. Monismith, D. Epel and R.N. Zare (Stanford University Bio-X Interdisciplinary Initiative Program and collaborators at the US Geologic Survey, Menlo Park, CA) Organic contaminants in sediments pose long-term risks to human health and the environment. This project seeks to understand how the binding of organic contaminants with sediment particles affects the uptake and accumulation of polychlorinated biphenyls [PCBs] and polycyclic aromatic hydrocarbons [PAHs] by particle-feeding organisms, such as clams native to San Francisco Bay.

Characterization of Lampblack Materials in Soils - Luthy, R.G. (Gas Technology Institute, Chicago, IL) Lampblack was produced as a by-product from the former oil gasification processes used in California. The distribution and binding of polycyclic aromatic hydrocarbons [PAHs] in lampblack material from field sites are studied to assess how this material binds the PAHs and reduces exposure.

Microscale Characterization of the Binding and Sequestration of Nitroaromatics in Soils - Luthy, R.G. and U. Ghosh (US Army Engineer Research and Development Center, Vicksburg, MS, and University of Notre Dame) Microscale analytic techniques are applied to soils contaminated with TNT to assess whether crystalline TNT exists in the soil and how this affects the biotreatability of TNT-impacted soils from Army ammunition sites.

PAH and PCB Binding to Sorbent Material - Luthy, R. G. (Ford Motor Company) Mass transfer and phase partitioning studies are evaluating the rate of transfer of PAHs and PCBs from contaminated sediment to sorbent material.

Cyanide Measurement and Chemistry in Wastewater Effluent - Luthy, R. G. (Water Environment Research Foundation and others; with Carnegie Mellon University, Malcolm Pirnie, Inc and Clarkson University) A multi-investigator project is evaluating cyanide measurement and speciation at low levels in chlorinated effluent. The effect of chlorination on possible formation of cyanide at low levels is studied. The collaborators include various large municipal wastewater treatment plants across the United States. (with David A. Dzombak, Carnegie Mellon University)

Mobility of PCBs in Contaminated Soils/Sediments - Luthy, R. G. (US EPA) A novel passive, wick sampler is designed to measure hydrophobic organic compounds in soil pore water. Laboratory tests assess the device's hydraulic performance and capture efficiency for chlorinated aromatics. The role of separate phase oil containing PCBs is modeled to evaluate the release of PCBs from hydraulic oils in sediment and soil (Sean McNamara).

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