Download or read book Modeling of Colloid Facilitated Contaminant Transport in Unsaturated Porous Media written by Heecheul Choi and published by . This book was released on 1995 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling Colloid Facilitated Groundwater Contaminant Transport written by Shiyan Jiang and published by . This book was released on 1993 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Influences of Flow Transients and Porous Medium Heterogeneity on Colloid Associated Contaminant Transport in the Vadose Zone written by and published by . This book was released on 2003 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Influences of Flow Transients and Porous Medium Heterogeneity on Colloid Associated Contaminant Transport in the Vadose Zone written by Joseph Ryan and published by . This book was released on 2003 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Modelling of Pollutants in Complex Environmental Systems written by Grady Hanrahan and published by ILM Publications. This book was released on 2010 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Colloid Facilitated Transport of Radionuclides Through the Vadose Zone written by John F. McCarthy and published by . This book was released on 2006 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main purpose of this project was to advance the basic scientific understanding of colloid and colloid-facilitated Cs transport of radionuclides in the vadose zone. We focused our research on the hydrological and geochemical conditions beneath the leaking waste tanks at the USDOE Hanford reservation. Specific objectives were (1) to determine the lability and thermodynamic stability of colloidal materials, which form after reacting Hanford sediments with simulated Hanford Tank Waste, (2) to characterize the interactions between colloidal particles and contaminants, i.e., Cs and Eu, (3) to determine the potential of Hanford sediments for \textit{in situ} mobilization of colloids, (4) to evaluate colloid-facilitated radionuclide transport through sediments under unsaturated flow, (5) to implement colloid-facilitated contaminant transport mechanisms into a transport model, and (6) to improve conceptual characterization of colloid-contaminant-soil interactions and colloid-facili\-tated transport for clean-up procedures and long-term risk assessment. We have previously shown that upon contact with simulated waste tank solutions, Hanford sediments change their mineralogical composition. Certain minerals, i.e., quartz, smectite, and kaolinite, are partially dissolved, and new mineral phases, i.e., the feldspathoids cancrinite and sodalite, are formed. We have characterized these mineral transformations and clarified the mineral transformation pathways. The new minerals were mainly in the colloidal size fraction (diameter less than 2 mum), had a negative surface charge, and were microporous, meaning they contained small pores. When Cs was present during the formation of the minerals, contaminants, like Cs, could be trapped inside the mineral structure. Transport experiments under water saturated and unsaturated conditions showed that the colloids were mobile in Hanford sediments. As the water saturation of the sediments decreased, the amount of colloids transported also decreased. The colloids had the ability to enhance the migration of the radionuclide Cs; however, Cs initially sorbed to colloids was desorbed during transport through uncontaminated Hanford sediments. The finding that Cs was stripped off the colloids during the transport through uncontaminated sediments implies that colloids will likely not be an effective carrier for Cs, unless the Cs is incorporated into the mineral structure of the colloids such that the radionuclide cannot desorb from the colloids. Nevertheless, it appears that the amount of Cs that can be transported by mobile colloids beneath Hanford waste tanks is limited. Colloids will not be able to move the bulk mass of Cs through the vadose zone at Hanford. Colloid stability studies indicate that Hanford sediment form stable colloidal suspensions when suspended in Hanford sediment pore waters. Colloid stability was assessed by determination of the critical coagulation concentration, i.e., the chemical electrolyte concentration at which colloidal suspensions flocculate and settle out (become unstable). Although in the stable mode, Hanford colloids will settle out of solution after extended periods of time (months to years). Given the low recharge rates at Hanford range, which from near 0 to more than 100 mm/year, and the long travel times for rainwater to reach the groundwater of more than 40 years, it appears that colloidal transport is unlikely to occur if colloids are initially to be suspended close to the soil surface by infiltrating rainwater. However, if preferential flow or transient flow occurs, then colloidal transport may become more important. The results of this project have also led to improvements of our fundamental understanding of colloid transport and mobilization under unsaturated flow conditions in porous media. We have found that colloid attachment to the liquid-gas interface is not that relevant and that colloids rather attached near the triple phase interface where air, water, and solid phases meet. We have also found that capillary forces are the most dominant forces governing colloid release in unsaturated porous media. These results help to advance our understanding of colloid fate and transport in unsaturated porous media.

Download or read book Influences of Flow Transients and Porous Medium Heterogeneity on Colloid Associated Contaminant Transport in the Vadose Zone written by James Saiers and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Pore scale Investigation on Mechanisms of Colloid Retention in Unsaturated Porous Media written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloid-facilitated transport of contaminants and transport of biocolloids (e.g., viruses and bacteria) in soil porous media are acknowledged environmental issues. Understanding of the mechanisms and parameters controlling colloid transport is important for protection of soil and groundwater resources from bio- and chemical contamination and improvement of remediation practices. For research purposes, unsaturated soil is often represented with idealized porous media, which facilitates conceptual understanding of colloid transport and retention mechanisms. Major colloid retention mechanisms include retention at solid-water interface (SWI), at air-water interface (AWI), and on the contact line. Additional colloid retention occurs as a result of straining in the narrow, compared to colloid size, regions of porous media. Colloid retention at AWI and colloid retention on the contact line are characteristic of unsaturated porous media and are currently associated with substantial uncertainty in colloid transport literature regarding their respective roles and contributions to overall colloid retention. In order to distinguish colloid retention mechanisms, traditional laboratory column experiments often require supplementary pore-scale investigation. The focus of this research was to investigate colloid retention at AWI and contact line at the pore scale. In this work, open capillary channels and microfluidic channels were utilized as models of soil capillaries, and behavior of colloids was visualized directly with confocal microscope. The employed channels have angular cross sections, which is in agreement with a more realistic angular representation of soil capillaries. The open-channel configuration served as a model of free-surface flow in microscopic grooves and corners in soil while the microfluidic channels were used to represent two-phase (air-water) flow in soil such as during drainage and infiltration events. To acquire qualitative and quantitative information, experimental confocal images were recorded and systematically processed with advanced imaging software. Colloid behavior in open channels with square cross section was investigated both in static and dynamic regimes. During flow in the channel, colloid movement occurred along the contact line, which acted as a colloid accumulation site due to reduced velocities in the contact line region. For this channel configuration, flow stagnation at AWI was observed, which promoted colloid retention at AWI. The maximum velocity and therefore maximum colloid transport were observed inside the channel. These observations indicated the importance of hydrodynamic conditions in affecting colloid retention. In the static regime, effects of a number of physicochemical parameters on colloid retention at AWI, including ionic strength, colloid contact angle, and surface tension (addition of surfactant), were investigated. It was shown that retention of colloids at AWI was dependent on electrostatic conditions and colloid contact angle and varied to a lesser extent with addition of non-ionic surfactant. The retention of colloids at AWI in a static system was analyzed with extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and was attributed to a possible secondary energy minimum retention. In microfluidic channels, which have a trapezoid cross section, AWI was observed as a two-phase boundary. In such configuration, both AWI and contact line move in the flow direction. It was shown that colloid retention on the contact line was considerably affected by hydrodynamic conditions. Colloid retention at AWI occurred primarily via involvement of colloids, which were previously deposited on the wall, with the moving contact line. Direct retention of dispersed colloids at AWI was not observed. The moving AWI was realized both as receding (air) and advancing (water) fronts, which allowed examination of the role that AWI played in colloid mobilization under both drainage and infiltration scenarios. Experimental results were considered in view of colloid interaction energies as well as forces acting on colloids at the sites of interest. Both experimental and theoretical findings resulted in improved understanding of colloid retention at AWI and contact line in the considered configurations, i.e., open channel and two-phase flows. The results of this research provide mechanistic understanding of colloid retention and can be applied in interpretation of observations at larger scales and in modeling of colloid transport in unsaturated porous media. This dissertation is accompanied with supplementary material showing representative video images and illustrating the discussed processes. System requirements for viewing the video: Windows Media Player or RealPlayer.

Download or read book Mathematical and Numerical Modeling of Contaminant Transport in Aqueous Systems Involving Mobile Solid Phases written by Arash Massoudieh and published by . This book was released on 2006 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling of Contaminant colloid Transport and Unsaturated Flow in Fractured Media written by Assem Abdel-Salam and published by . This book was released on 1995 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Colloidal Transport in Porous Media written by Fritz H. Frimmel and published by Springer Science & Business Media. This book was released on 2007-05-26 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Colloid Mobilization and Transport in Contaminant Plumes written by and published by . This book was released on 1999 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Colloid Transport in Saturated Porous Media written by Ann Mathew and published by . This book was released on 2007 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Colloid facilitated Transport of Contaminants in Porous Media written by Sujoy B. Roy and published by . This book was released on 1995 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Colloid and Surfactant Transport Modeling Through Agricultural Soil written by Sandip Raman Patil and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: National Water-Quality Assessment Program (NAWQA) was designed just after the U.S. Geological was established. The primary objective of the NAWQA was to understand the key processes controlling contaminant fate and transport into the Nation's water resources. In particular, wide use of pesticides and fertilizers in agricultural field can impact on the quality of surface and ground waters. Contaminants can be carried to the water bodies by several ways. In colloid-facilitated transport process colloidal particles serves as a transport media for the contaminants. Colloid release from the agricultural soil under unsaturated conditions is controlled by the hydrodynamic force, capillary force and electrostatic force that is determined by the solution chemistry in terms of solution ionic strength and pH. In this research, colloid release from the agricultural soil was investigated using an intact soil column collected from an agricultural site in Gadsden County of Florida. Colloid release was monitored and the colloid release curve was simulated using an implicit, finite-difference scheme to obtain the colloid release coefficient. It was found that the hydrodynamic force and electrostatic force overcame the capillary force under the experimental conditions of this research and consequently, colloids were released. For the colloid release, solution chemistry played a key role by controlling the colloid repulsive electrostatic force within the pore system. Colloid release exponentially decreased with the increase of solution ionic strength and increased with the increase of solution pH. Colloid release was finally found to be correlated to the colloid repulsive electrostatic force within the pore system, i.e., the greater the repulsive electrostatic force, more colloids were released. In situ colloid mobilization and transport has been studied under both saturated and unsaturated conditions. In saturated conditions, the controlling parameters are solution ionic strength and pH. Colloid mobilization and transport have been modeled by the advection-dispersion equation with a first-order colloid release. The inverse version of these models can provide a platform to estimate transport parameters based on transport observations. In this research, we taken the advantages of existing contaminants transport models by fully utilizing them to investigate colloid interactions with the surrounding environment and provide parameter constraints for colloid transport modeling applications under saturated conditions. In natural systems, colloids present a potential health risk due to their propensity to associate with contaminants or in the case of certain biological colloids, inherent pathogenic nature. Although colloidal interactions have been studied for many years and much has been learned about the physical and chemical processes that control colloid retention, there still remains significant uncertainty about the processes that govern colloid release. The aim of this study was to investigate the release of in situ colloids as a function of soil depth. Colloid release from intact agricultural soil columns with variable length was investigated. Colloid release curves were simulated using an implicit, finite-difference scheme and colloid release rate coefficient was found to be an exponential function of the soil depth. The simulated results demonstrated that transport parameters were not consistent along the depth of the soil profile. Wetting agents wet hydrophobic soil by lowering the cohesive and/or adhesive surface tension, which allows the water to spread out more evenly and allows for better penetration into the hydrophobic soils. While enhancing water penetration, wetting agent applications may bring adverse impact on the soil and groundwater at the same time. The residual organic phase in the soil pores poses a long-term source of groundwater contamination. After use, residual wetting agents and their degradation products are discharged to groundwater or directly to surface waters, then dispersed into different environmental compartments. In order to assess their environmental risks, we need to understand the distribution, behavior, fate and biological effects of these surfactants in the environment. This research was designed to investigate the application of nonionic wetting agents in agricultural soils. Performance of nonionic surfactants in intact soil columns collected from agricultural soils was explored and related to the soil and wetting agent properties. In addition, the impact of the organic concentration of wetting agent fate and transport was investigated. The transport of wetting agents in the agricultural soil columns was simulated using the proposed transport models and subsequently, the effect of organic compounds on wetting agent transport was quantified.

Download or read book Modeling and Experimental Validation of Colloid Facilitated Cesium Transport in Porous Media written by Alan Lee Noell and published by . This book was released on 1996 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluation of Colloid Facilitated Transport of Chromium Through Saturated Porous Media Using Column Experiments written by Joseph E. Bonetti and published by . This book was released on 1995 with total page 600 pages. Available in PDF, EPUB and Kindle. Book excerpt: