Landfill covers systems are designed to isolate contaminants from the environment for hundreds to thousands of years. In the long term, however, the landfill covers are susceptible to failure caused by physical, chemical and biological effects. Plant intrusion is a major concern of landfill sustainability; the roots of plants have been found to increase the soil hydraulic conductivity by two orders of magnitude. The objective of this thesis was to evaluate the effect of plant intrusion and the resulting increase in the saturated hydraulic conductivity on the water balance of landfill cover systems. The finite element software model HYDRUS-1D was used to simulate water flux and root water uptake processes. Plant growth effects on the Burrell, Pennsylvania, uranium mill tailings site were evaluated as a case study. Additionally, a comparison of the water balance and effects of plant growth for different landfill cover designs (RCRA Subtitle C, RCRA Subtitle D and evapotranspiration covers) was performed. For each of the cases, different precipitation events were used to simulate arid and humid conditions. The plant roots effectively reduced the water content in the landfill cover systems, and it was concluded that vegetation should not be eliminated once established.

The inherent heterogeneity of subsurface porous media, as well as the occurrence of highly non-linear rate-limiting mass transfer processes, results in significant challenges to accurate and efficient modeling of contaminant flow and transport. This dissertation provides comprehensive Web-based modeling tools and advanced numerical methods for students and researchers to better investigate fluid flow and mass transfer processes in natural and model systems under water-saturated conditions. A Web-based virtual mass transfer processes laboratory (MTVLab) was developed for students and researchers to access and study state of the art understanding of mass transfer mechanisms at the particle scale. Meanwhile, MTVLab system architecture provides a proof-of-principle framework from which to develop more sophisticated Web-based models that can employ computationally efficient, high-level computer programs. MTVLab is available at http://www.vanderbilt.edu/mtvlab. Lattice Boltzmann methods (LBM) were used to study fluid flow in two-dimensional randomly generated porous media. An innovative method was developed to construct permeability cumulative distribution functions through the combination of LBM and first order reliability method (FORM). LBM FORM was found to be approximately 13 to 120 times more efficient than traditional Monte Carlo-based simulations while maintaining similar orders of accuracy. A novel least squares finite element lattice Boltzmann method (LSFE-LBM) was developed, extending LBM to unstructured meshes. LSFE-LBM is able to more efficiently simulate fluid flow and solute transport in domains that contain complex or irregular geometric boundaries. LSFE-LBM provided the foundation for the numerical modeling efforts to elucidate the relative contributions of transport-related and sorption/desorption - related nonequilibrium factors on mass transfer processes in a whole class of porous media exemplified by randomly generated porous media. Applications of LSFE-LBM to simulate phenanthrene transport in porous media represent an initial effort to bridge comprehensive sorption/desorption mechanistic studies with porescale modeling, the results of which help advance our understanding of the effects of soil organic matter and soil structure configurations on fate and transport of organic chemicals in subsurface systems.

Hillslope soils cover a large proportion of Earths terrestrial landscapes. This dissertation is a theoretical exploration of how chemical and mechanical processes affect the formation and dynamics of both hillslope soils and soil mantled landscapes. It explores how hillslopes adjust to time varying erosion rates. Statements of mass conservation for both the total soil layer and constitutive soil phases are derived that include terms describing both chemical and mechanical denudation. These statements are used to demonstrate that chemical processes are as important as mechanical processes in determining the morphology of landscapes, and that chemical properties of hillslope soils can be used to quantify chemical denudation rates. Analyses are performed for both the steady state case (where erosion rates do not change in time) and the transient case (where erosion rates are time-varying). Transient simulations show that hillslope soils respond to changes in channel incision over characteristic timescales, and changes in channel incision leave characteristic chemical and physical signatures on the landscape that last for tens of thousands to millions of years.

Rapid testing procedures are desirable for evaluating leaching from secondary materials being considered for beneficial use in construction or disposal. Often, column leaching tests are considered a surrogate for field data, providing a basis to estimate constituent release under field conditions of intermittent infiltration. This dissertation evaluates the use of batch leaching tests providing information as a function of pH and liquid to solid ratio as a basis for estimating constituent leaching under intermittent percolation. Batch testing results are compared to column testing under unsaturated, intermittent flow and continuous saturated flow. Extrapolations from batch testing based on empirical relationships of pH and liquid to solid ratio and the use of geochemical speciation modeling to represent leaching behavior are examined. Uncertainties as a consequence of each extrapolation basis are quantified. Five granular materials with potential for reuse were evaluated: municipal solid waste incinerator bottom ash, coal fly ash, aluminum recycling residue, construction demolition debris, and a synthetic cement mortar. Two of these materials were tested under two different aging conditions. Results showed no significant difference between the continuously saturated and intermittent unsaturated column flow regimes, agreement in most cases between batch and column testing, including cumulative release, and a decrease in constituent release due to carbonation. Geochemical speciation modeling results for three selected materials agree with experimental batch data and may be used for long-term constituent release prediction.

Soil vapor extraction (SVE) is the most popular technology for removing volatile contaminants from the vadose zone. However, SVE is limited by the contaminant vapor pressure, hydraulic conductivity and gas permeability of the vadose stratigraphy. Concentration reductions greater than 90% are hard to achieve with traditional SVE. Thermal enhancement is establishing itself as a viable method to increase the applicability and effectiveness of SVE. Heating methods include steam injection, radiowave, microwave, and electrical resistance. The appropriate method depends on site geology, soil and contaminant parameters and the maximum temperature required. Electrical resistance heating (ERH) is one promising enhancement method. ERH has been demonstrated at more than 30 sites. However, little is known about the mechanisms occurring during the heating process. Existing models are limited in scope, neglecting important aspects of heat and mass transfer. The purpose of the research presented is to develop the basis for a general mass transfer model to simulate the SVE process during remediation of chlorinated solvents using thermally enhanced SVE in the vadose zone. A conceptual model detailing the processes occurring during vapor extraction with soil heating by electrical resistance is proposed. The conceptual model is then used to derive a set of governing equations for a general multiphase multicomponent system with an applied heat flux. This approach allows the model developed here to be extended to other thermal treatments.

The removal (biodegradation and air-stripping) of some common VOCs, including benzene, toluene, TriChloroEthylene (TCE), methylene chloride, and Methyl IsoButyl Ketone (MIBK) was evaluated for aerobic biological treatment processes. The methodology used laboratory-scale data (aqueous input and output) for oxygen demand and VOCs to estimate mass transfer parameters and eliminate the need to simultaneously calculate removal by biodegradation and air stripping. First, a dimensionless parameter (ratio of VOC removed to estimated VOC air-stripping rate), ã, was developed, where ã < 1.0 implied that air stripping could be significant. This compared well to laboratory-scale data in each case (for example: toluene: ã = 0.615, air stripped = 8.18%; MIBK: ã = 42.1, air stripped = 0.18%). Finally, a stochastic model was developed (based on steady-state mass balances) to predict the amount of VOC air stripped. Conventional process parameters (normal distributions) were used to estimate the overall mass transfer coefficient for oxygen, (KLa)O, and this was used to estimate the overall mass transfer coefficient for each VOC, (KLa)VOC (based on a two-film model). The calculated results compared well with laboratory scale measurements, i.e., the calculated mean air stripping values were all within ±1.5 standard deviations of the mean observed experimental values. This prediction method is generally useful because the calculation does not contain the additional uncertainty from the bio-kinetic parameters.

Leaching tests are important laboratory tools that provide a method to determine the leachability and mobility of contaminants in the environment. Although a wide variety of leaching tests are available in the literature, few address the effect of oxidation/reduction reactions on contaminant release. In the laboratory, reducing conditions have been studied using biological methods, chemical reducing agents, and electrolytic techniques. Electrolytic techniques involve applying an electrolytic potential in order to change the redox of the system and were chosen for this research in order to eliminate the use of chemical reducing agents and microorganisms. The specific objectives of the research presented here were to: 1) develop an apparatus based on electrolytic techniques and 2) use the apparatus to determine the effect of time and varying potentials on changes in suspension pH, Eh, and constituent solubility. These objectives were met through two sets of studies: 1) preliminary studies using sampled-current voltammetry experiments consisting of cyclic potential sweeps and 2) electrolytic oxidation/reduction studies. Three different systems were used: 1) an iron(III) nitrate solution (test system), 2) an arsenic contaminated soil suspension (naturally oxidized system), and 3) a furnace slag suspension (naturally reduced system). The electrolysis technique was shown to be capable of changing the bulk solution Eh, pH, and constituents concentrations. However, further research must be completed in order to further explore the capability of this method.

This study systematically investigated the effects of aerosol chemical composition on SOA production in real atmosphere. The findings in this study help reveal the interactions between individual aerosol components and the subsequent effects on secondary organic aerosol (SOA) partitioning. The aerosol code in the CMAQ model was modified to incorporate structure information and partitioning parameters of lumped SOA product groups, which are formulated directly from the corresponding properties of the individual SOA products. The updated CMAQ was evaluated against field measurements, from two monitoring networks IMPROVE and SEARCH and one field study - Southern Oxidants Study (SOS99), in the Nashville region during the summer of 1999. It is found that POA composition representation greatly affects the quantification of the composition effects on SOA production. While assuming aerosol phase activity coefficients are 1 for all organics is a good approximation to speed up the simulation for an aerosol mixture solely composed of wood smoke and SOA components, for a mixture of diesel soot and SOA products, making such a simple assumption would result in a great overprediction of the ambient SOA concentrations. Simulations were also conducted to study the influence of model parameters of great uncertainty such as the vaporization enthalpy of the individual SOA products and the number of lumped groups used to represent SOA production. Simulation results indicate that the vaporization enthalpy for the SOA components need more research efforts due to its significant effects on the predicted SOA concentrations. It is also worthwhile to pay attention to the number of lumped groups applied in air quality simulation. The effects of water absorbing into the aerosol phase were also studied. Allowing water absorbing into the aerosol phase improves the model prediction on SOA concentration in this study. However, the CPU time is increased by several times compared to that required for the base case simulation. This new module is not only applicable to CMAQ, but also can be incorporated into other air quality models.

This dissertation details the development of a consequence management system for water utilities, which determines the optimal operational response to a contamination event in a water distribution network. In order to develop an effective emergency response plan, water utilities need to explore different operational response actions for the most optimal strategy. By coupling an optimization methodology with a hydraulic and water-quality model, an optimal consequence management strategy can be identified for a specific contamination event. The set of consequence management strategies produced from this research identified protocols to best isolate an event and manage response measures. With the incorporation of spatial information, the concerns of critical customers can be addressed when determining an optimal consequence management strategy. The consequence management tool will be useful to water utilities for both planning emergency response scenarios and responding to an emergency in real-time. With this knowledge, water utility managers will be better prepared to mitigate attacks against water distribution networks.

Hospitals play a primary role in a community during mass casualty events. To optimize community response to a disaster, it is crucial for local and state emergency management agencies (EMAs) to have pre-established and well-developed communication, information, and resource (CIR) management linkages with local hospitals since they cannot effectively provide patient care if they are rendered non-operational. The objectives of this research were three-fold: (1) to determine the current state, post 9/11/01, of CIR management linkages during mass casualty events among EMAs and area hospitals in large U.S. cities; (2) to identify and investigate a real-world model of strong CIR linkages; and (3) to determine how weaknesses in current CIR linkages could be strengthened, including the role of information technology in supporting these improvements. The objectives were accomplished by initially reviewing historical CIR linkages among EMAs and hospitals. This served as the foundation for the development and conduct of a survey to determine the state of the practice, post 9/11, of CIR linkages among hospitals and EMAs in several large cities across the country. Of particular interest was whether the post-9/11 influx of resources and attention to emergency preparedness concerns had yielded any improvements in CIR linkages. The results of this effort are presented, along with key research findings and recommendations for future improvements in CIR linkages among EMAs and hospitals to optimize community mass casualty event response. This includes a best practices case study of relationship and linkage-building efforts in Phoenix, Arizona.