The effect of water content and soil-water hysteresis on transport of unreactive water-tracers and volatile organic compounds (VOCs) in porous media is investigated under steady-state water-flow conditions. Specifically, this research addresses the effect on dispersive and mass transfer processes affecting the movement of NaC1 and trichloroethene (ICE) and how these processes influence the approach to Fickian flux conditions. Transport experiments were conducted in a 25-cm column packed with silica sand. Based on the results, it is concluded that water content (0), pore-water velocity, and flow history affect the average movement and spread of water-tracers and VOCs. It is suggested that non-volatile solutes in unsaturated media travel longer distances or times to achieve a Fickian state. Consequently, a greater number of averaged heterogeneities are encountered and solute flux is characterized by a greater dispersion coefficient (D). A power (n) law relationship (D(m) = η(v(m)/ θ(m))ⁿ), found between mobile dispersion coefficients (D(m_), pore-water velocity (v(m)), and water content (θ(m)) for different porous media, indicates that dispersivity (η) is not only a function of the media, but also of θ(w). TCE transport is controlled by advection processes for Ow greater than 50% saturation. Lower θ(w) result in greater TCE dispersion, retardation, mass-transfer resistance, vapor diffusion, and spreading. Consequently, VOCs reach the Fickian regime at shorter distances than unreactive solutes in water. Although VOC transport is influenced by multiple rate-limited mass transfer, the mechanisms controlling the overall mass-transfer resistance vary as a function of θ(w). The hysteretic behavior of solute transport parameters is attributed to a greater degree of irregular flow paths and entrapped air, higher air-water interfacial areas, and thicker water-films for wetting than draining scenarios. Consequently, wetting conditions result in slower mixing (up to 98% lower mass-transfer coefficients) of dissolved solutes. Since TCE transport at low water contents and wetting conditions is dominated by diffusion and dispersion mechanisms, the TCE velocity distribution in the liquid phase is normalized by velocity distributions in the gas-phase and becomes closer to Fickian conditions.

Mak Chung Ming = 多孔介質中的局部性與整體性漲落 / 麥仲明. / Thesis submitted in: July 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 116-123). / Text in English; abstracts in English and Chinese. / Mak Chung Ming = Duo kong jie zhi zhong de ju bu xing yu zheng ti xing zhang luo / Mai Zhongming. / Abstract (in English) --- p.i / Abstract (in Chinese) --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.ix / Chapters / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Motivation of research on porous medium --- p.1 / Chapter 1.2 --- Description of porous medium --- p.2 / Chapter 1.3 --- Brief history of research of thermal convection in porous medium --- p.5 / Chapter 2. --- Background --- p.7 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- Governing equations and parameters --- p.8 / Chapter 2.3 --- Review of literature --- p.15 / Chapter 2.4 --- Summary --- p.20 / Chapter 3. --- Instrumentation --- p.21 / Chapter 3.1 --- Experimental setup --- p.21 / Chapter 3.1.1 --- Porous medium --- p.21 / Chapter 3.1.2 --- Working fluid --- p.24 / Chapter 3.1.3 --- Container cell --- p.25 / Chapter 3.1.4 --- Top plate --- p.26 / Chapter 3.1.5 --- Bottom plate --- p.28 / Chapter 3.2 --- Thermistors and its calibration --- p.28 / Chapter 3.3 --- Other apparatuses --- p.31 / Chapter 4. --- Data analysis and results --- p.33 / Chapter 4.1 --- Measurement of global heat flux --- p.33 / Chapter 4.1.1 --- Heat transfer characteristic --- p.34 / Chapter 4.2 --- Local temperature measurements --- p.37 / Chapter 4.2.1 --- 3mm bead´ؤwater system (small cell) --- p.38 / Chapter 4.2.2 --- 6mm bead´ؤwater system (small cell) --- p.44 / Chapter 4.2.3 --- 6mm bead´ؤwater system (large cell) --- p.64 / Chapter 4.2.4 --- 10mm bead´ؤwater system (large cell) --- p.76 / Chapter 4.3 --- Correlation of the time series --- p.96 / Chapter 4.4 --- Thermal pulse experiment --- p.101 / Chapter 5. --- Conclusions --- p.111 / Appendix --- p.114 / Bibliography --- p.116

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Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (p. [138]-148).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Todd Arbogast. Vita. Includes bibliographical references.

Several factors which affect the transport of pyridine, quinoline and acridine (aza-arenes) in saturated porous media were investigated in laboratory experiments in order to provide data for input into coupled models that may be applied to predicting the fate of these compounds in groundwater. The effect of pH and ligand type and concentration on acridine solubility was studied in a series of batch and pH-stat experiments. There was a decrease in acridine solubility below the compound's pKₐ due to acridine/ligand precipitate formation. The reaction stoichiometry and solute/sorbent interactions of aza-arene adsorbed to porous silica were determined from batch adsorption and Raman spectroscopy experiments. The neutral aza-arene was hydrogen bonded to surface sites above the compound's pKₐ and there was a cation/ClO₄⁻ complex interacting with surface sites through dipole-dipole interactions below the pKₐ of the compound. The effect of pH, temperature, ligand type, average linear velocity and initial aqueous phase solute concentration on the adsorption of aza-arenes to porous silica was investigated in a series of column experiments. The extent of adsorption followed the trend pyridine < quinoline < acridine due to greater overlap of the molecule with adsorption sites as the number of rings increases. The extent of adsorption was greater below the compound's pKₐ than above because the complex was able to optimize its orientation with the surface. The extent of adsorption of neutral acridine was enhanced when carbonate was used as a buffer relative to phosphate due to carbonate's more exothermic hydration enthalpy. The isotherms were non-linear above and below the pKₐ of acridine. The enthalpy of the adsorption reaction was less exothermic below the compound's pKₐ than above due to the stronger hydrogen bonds formed between the surface and the neutral molecule compared to the dipole-dipole interactions that bond the complex to the surface below the pKₐ. Non-equilibrium effects on the adsorption reaction were minor. Adsorption-desorption was on the order of seconds to minutes. Kinetic effects became more important as temperature decreased.

The effectiveness of a cyclodextrin (sugar-based) solution for enhancedsolubilization removal of multicomponent nonaqueous phase organic liquid (NAPL) contamination from an aquifer is tested in a pilot-scale field experiment. This effort is the first field test of this innovative technology, termed a "Complexing Sugar Flush" (CSF). The saturated zone within an enclosed cell was flushed with 8 pore volumes of 10wt% cyclodextrin solution. The cyclodextrin solution increased the aqueous concentrations of all the target contaminants to values from about 100 to more than 20,000 times the concentrations obtained during a water flush conducted immediately prior to the CSF. The degree of solubility enhancement was greater for the morehydrophobic contaminants. Conversely, the relative mass removal was greater for the less-hydrophobic compounds due to their generally higher apparent solubilities. The average reduction in NAPL mass for the target contaminants was about 41%. A relationship is developed to describe enhanced dissolution of a multiple-component NAPL, and is used to analyze the field data. The effluent concentrations for most of the target contaminants during the cyclodextrin flush were within a factor of two of the equilibrium values predicted using this theory. Deviations from ideal dissolution behavior were also observed. Finally, the cyclodextrin solution appeared to significantly enhance both the magnitude and the rate of NAPL dissolution compared to a water flush conducted prior to the cyclodextrin flush. These results contribute to a better understanding of the important physicochemical processes involved in using enhancedsolubilization agents for the remediation of multiple-component NAPLs.

We consider steady state unsaturated flow in bounded randomly heterogeneous soils under influence of random forcing terms. Our purpose is to predict pressure heads and fluxes and evaluate uncertainties associated with these predictions, without resorting to Monte Carlo simulation, upscaling or linearization of the constitutive relationship between unsaturated hydraulic conductivity and pressure head. Following Tartakovsky et al. [1999], by assuming that the Gardner model is valid and treating the corresponding exponent a as a random constant, the steady-state unsaturated flow equations can be linearized by means of the Kirchhoff transformation. This allows us develop exact integro-differential equations for the conditional first and second moments of transformed pressure head and flux. The conditional first moments are unbiased predictions of the transformed pressure head and flux, and the conditional second moments provide the variance and covariance associated with these predictions. The moment equations are exact, but they cannot be solved without closure approximations. We developed their recursive closure approximations through expansion in powers of σᵧ and σᵦ, the standard deviations of Y = lnK(s), and β = ln α, respectively, where K(s), is saturated hydraulic conductivity. Finally, we solve these recursive conditional moment equations to second-order in σᵧ and σᵦ, as well as second-order in standard deviations of forcing terms by finite element methods. Computational examples for unsaturated flow in a vertical plane, subject to deterministic forcing terms including a point source, show an excellent agreement between our nonlocal solutions and the Monte Carlo solution of the original stochastic equations using finite elements on the same grid, even for strongly heterogeneous soils.

This dissertation examines three different aspects of groundwater contamination by immiscible liquids, both at laboratory and field scale. The first component incorporates a study of denser than water immiscible-liquid dissolution at the laboratory scale that aims to describe the effects of immiscible liquid source-zone saturation, distribution, and length on dissolution rates. It was observed that overall immiscible-liquid saturation, distribution, and source zone length did not influence initial dissolution rates under the condition of the experiments. However, transient phase dissolution behavior, primarily observed by the heterogeneously packed columns, was significantly different to that of the homogeneously packed columns. This indicates that initial dissolution rates are comparable for these different systems, however it is demonstrated that immiscible liquid distributions (e.g., heterogeneity) can significantly effect transient dissolution rates. The second component investigates the effectiveness of a field-scale partitioning tracer test (PTT) for the measurement of the amount of denser than water immiscible liquid in the subsurface. It was demonstrated that the effectiveness of partitioning tracer test may be significantly limited by factors contributing to nonideal transport such as sorption, tracer mass, and immiscible liquid distribution. The third component examines the effectiveness of a field-scale remediation technology for the enhanced removal of denser than water immiscible liquid in the subsurface. An important component of this project was the implementation of reagent recovery and reuse, which improved the efficiency of the technology. It was demonstrated that the effectiveness of enhanced solubilization technologies for groundwater remediation may be significantly limited by the distribution of immiscible liquid in the subsurface. However, the nature of cyclodextrin (enhanced-solubilization agent) makes it an attractive option for subsurface remediation of immiscible-liquid contaminants, especially for situations where mobilization is undesirable and where the use of higher-toxicity agents is not possible.

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