Influences of Flow Transients and Porous Medium Heterogeneity on Colloid-Associated Contaminant Transport in the Vadose Zone PDF Download
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Languages : en
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Our research is guided by an EMSP objective to improve conceptual and predictive models of contaminant movement in vadose-zone environments. As described in the report National Roadmap for Vadose-Zone Science and Technology [DOE, 2001], soil-water colloids are capable of adsorbing contaminants, such as radionuclides and metals, and facilitating their migration through the vadose zone and towards groundwater reservoirs. Our research centers on advancing understanding of this phenomenon. In particular, we are combining mathematical modeling with laboratory experimentation at pore and column scales to (1) elucidate the effects of porewater-flow transients on colloid mobilization in unsaturated porous media; (2) explore the sensitivity of colloid deposition rates to changes in porewater chemistry and colloid mineralogy; (3) develop mathematical models appropriate for simulating colloid mobilization, transport, and deposition under both steady-flow and transient-flow conditions; (4) identify mechanisms that govern mineral-colloid mobilization and deposition in unsaturated porous media; (5) quantify the effects of mineral-grain geometry and surface roughness on colloid-filtration rates; and (6) evaluate the influences of colloids on the transport of strontium and cesium (i.e., DOE-contaminants-of-concern) through soils and sediments.
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Languages : en
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Book Description
Our research is guided by an EMSP objective to improve conceptual and predictive models of contaminant movement in vadose-zone environments. As described in the report National Roadmap for Vadose-Zone Science and Technology [DOE, 2001], soil-water colloids are capable of adsorbing contaminants, such as radionuclides and metals, and facilitating their migration through the vadose zone and towards groundwater reservoirs. Our research centers on advancing understanding of this phenomenon. In particular, we are combining mathematical modeling with laboratory experimentation at pore and column scales to (1) elucidate the effects of porewater-flow transients on colloid mobilization in unsaturated porous media; (2) explore the sensitivity of colloid deposition rates to changes in porewater chemistry and colloid mineralogy; (3) develop mathematical models appropriate for simulating colloid mobilization, transport, and deposition under both steady-flow and transient-flow conditions; (4) identify mechanisms that govern mineral-colloid mobilization and deposition in unsaturated porous media; (5) quantify the effects of mineral-grain geometry and surface roughness on colloid-filtration rates; and (6) evaluate the influences of colloids on the transport of strontium and cesium (i.e., DOE-contaminants-of-concern) through soils and sediments.
Author: Joseph Ryan
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Languages : en
Pages : 5
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We are investigating the role of colloids in the movement of radionuclides through water unsaturated porous media. This research is guided by a key objective of the Environmental Management Science Program (EMSP), which is to improve conceptual and predictive models for contaminant movement in complex vadose zone environments. In the report entitled National Roadmap for Vadose Zone Science and Technology [DOE, 2001], increases in the understanding of colloid-contaminant interactions, colloid mobilization, and colloid deposition within unsaturated soils are cited as requisite needs for predicting contaminant fate and distribution in the vadose zone. We seek to address these needs by pursuing three overarching goals: (1) identify the mechanisms that govern colloid mobilization, transport, and deposition within unsaturated porous media; (2) quantify the role of colloids in scavenging and facilitating the transport of radionuclides; and (3) develop and test a mathematical model suitable for simulating the movement of colloid associated radionuclides through variably saturated porous media.
Author: James Saiers
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Languages : en
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Radionuclides, metals, and dense non-aqueous phase liquids have contaminated about six billion cubic meters of soil at Department of Energy (DOE) sites. The subsurface transport of many of these contaminants is facilitated by colloids (i.e., microscopic, waterborne particles). The first step in the transport of contaminants from their sources to off-site surface water and groundwater is migration through the vadose zone. Developing our understanding of the migration of colloids and colloid-associated contaminants through the vadose zone is critical to assessing and controlling the release of contaminants from DOE sites. In this study, we examined the mobilization, transport, and filtration (retention) of mineral colloids and colloid-associated radionuclides within unsaturated porous media. This investigation involved laboratory column experiments designed to identify properties that affect colloid mobilization and retention and pore-scale visualization experiments designed to elucidate mechanisms that govern these colloid-mass transfer processes. The experiments on colloid mobilization and retention were supplemented with experiments on radionuclide transport through porous media and on radionuclide adsorption to mineral colloids. Observations from all of these experiments - the column and visualization experiments with colloids and the experiments with radionuclides - were used to guide the development of mathematical models appropriate for describing colloids and colloid-facilitated radionuclide transport through the vadose zone.
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Languages : en
Pages : 5
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During the past year (June 2003 to June 2004), work at Yale has centered on investigating the influences of porewater pH, flow transients, and the presence of natural organic matter (NOM) on the deposition and mobilization of clay colloids (kaolinite and illite) within columns packed with unsaturated porous media. The experiments on pH and flow-transient effects were described in our First-Term Progress Report (which covered the initial 18 months of the study) and will not be repeated here. More recent experiments on the role of NOM in colloid transport proved equally as interesting. Even at porewater concentrations as low as 0.2 mg/L, soil-humic acid substantially lowered clay-colloid deposition rates compared to the case in which soil-humic acid was absent from the porewater. We attribute this to adsorption of the humic acid to the positively charged edge sites of the clay colloids, which effectively reduced the colloid affinity for negatively charged air- and solid-water interfaces. Comparison of the results of the column experiments to calculations of a new mathematical model has sharpened our inferences regarding mechanisms that govern the rate-limited deposition and mobilization of colloids. We are testing these inferences by carrying out flow-and-transport visualization experiments. We have constructed a semi-transparent representation of a porous medium, consisting of a rectangular parallel-plate chamber that encloses 3-5 layers of uniformly sized sand grains. Ceramic plates fused to the ends of the chamber maintain the capillary tension and syringe pumps (located at the inlet and outlet ends) regulate the flow of water and colloids through the partially saturated sand. By placing the chamber beneath a microscope, we can examine the distribution of colloids between air-water and solid-water interfaces, directly measure the kinetics of deposition onto these interfaces, and observe the mechanisms that contribute to the release of immobile colloids. To date, we have used fluorescent microspheres as the colloids, but, once we refine our methodology, we intend to use clay particles as the colloids.
Author: Grady Hanrahan
Publisher: ILM Publications
ISBN: 1906799016
Category : Nature
Languages : en
Pages : 489
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Book Description
Environmental modelling has enjoyed a long tradition, but there is a defined need to continually address both the power and the limitations of such models, as well as their quantitative assessment. This book showcases modern environmental modelling methods, the basic theory behind them and their incorporation into complex environmental investigations. It highlights advanced computing technologies and how they have led to unprecedented and adaptive modelling, simulation and decision-support tools to study complex environmental systems, and how they can be applied to current environmental concerns. This volume is essential reading for researchers in academia, industry and government-related bodies who have a vested interest in all aspects of environmental modelling. Features include: A range of modern environmental modelling techniques are described by experts from around the world, including the USA, Canada, Australia, Europe and Thailand; many examples from air, water, soil/sediment and biological matrices are covered in detail throughout the book; key chapters are included on modelling uncertainty and sensitivity analysis; and, a selection of figures are provided in full colour to enable greater comprehension of the topics discussed.
Author: K. S. Birdi
Publisher: CRC Press
ISBN: 1420007203
Category : Science
Languages : en
Pages : 772
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Book Description
The third edition of this besteller covers the latest advancements in this rapidly growing field. Focusing on analyses and critical evaluation of the subject, this new edition reviews the most up-to-date research available in the current literature. International contributors offer their perspectives on various topics including micellar systems, mi
Author: François A. Richard
Publisher:
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Category :
Languages : en
Pages : 0
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Book Description
Our ability to predict solute transport in groundwater is limited by our imperfect understanding of the physical processes governing the spreading of underground contaminant plumes beneath the surface. Inaccurate prediction of solute migration can in turn result in unreliable risk analyses, or higher costs for groundwater decontamination. It is generally accepted that spatial variations in the hydraulic conductivity of porous materials largely contributes to the spreading of solutes dissolved in groundwater. Unsteady hydraulic gradients can also enhance this dispersion by imposing an additional source of variability on the flow field. Most field and numerical studies assume steady state groundwater flow, despite compelling field evidence suggesting that flow transience may be ubiquitous. This study characterizes the effects of transient groundwater flow on contaminant migration in both homogeneous and heterogeneous porous media. The macroscopic dispersion of miscible solutes subjected to unsteady flow fields is assessed quantitatively through a series of laboratory experiments and numerical simulations. An innovative laboratory model is presented, which consists of a two-dimensional flow cell and coupled hydraulic control system that allow the construction of spatially homogeneous or heterogeneous porous media of prescribed statistical properties, and to impose deterministic flow transients on the system. A monitoring procedure combining image processing with spatial moment analysis is used to characterize with great spatial and temporal resolution the evolution of contaminant plumes, as measured from sequences of digital images acquired during the course of laboratory experiments. Results suggest that the influence of flow transience on solute dispersion compares well with results reported in the literature, based on theoretical or numerical investigations. Changes in the mean flow direction significantly increase transverse dispersion in proportion to the rotation angle; conversely, longitudinal dispersivity decreases in response to variations in the flow direction, but to a lesser extent. Reversing hydraulic gradients can cause a reduction in the plume extents, or plume "shrinking". Although both the spatial and temporal variability enhance solute spreading, heterogeneity of the porous medium can mask the temporal variations in the flow field. The increased complexity introduced by the spatial and temporal variability can lead to inconsistencies between experimental and numerical models.
Author: John H. Cushman
Publisher: CRC Press
ISBN: 1315354535
Category : Science
Languages : en
Pages : 1726
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Book Description
This new edition adds several new chapters and is thoroughly updated to include data on new topics such as hydraulic fracturing, CO2 sequestration, sustainable groundwater management, and more. Providing a complete treatment of the theory and practice of groundwater engineering, this new handbook also presents a current and detailed review of how to model the flow of water and the transport of contaminants both in the unsaturated and saturated zones, covers the protection of groundwater, and the remediation of contaminated groundwater.
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Category : Colloids
Languages : en
Pages : 40
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Book Description
Author: Fritz H. Frimmel
Publisher: Springer Science & Business Media
ISBN: 3540713395
Category : Science
Languages : en
Pages : 294
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Book Description
This book covers the basics of abiotic colloid characterization, of biocolloids and biofilms, the resulting transport phenomena and their engineering aspects. The contributors comprise an international group of leading specialists devoted to colloidal sciences. The contributions include theoretical considerations, results from model experiments, and field studies. The information provided here will benefit students and scientists interested in the analytical, chemical, microbiological, geological and hydrological aspects of material transport in aquatic systems and soils.
