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Potentially hazardous waste materials (HWMs) are increasingly being recycled and used as highway construction and repair materials (CRMs). While reducing disposal costs, this practice raises concerns because hazardous organic pollutants (HOPs) from these wastes can leach from highways and enter soil surface and ground waters. This chapter presents the equilibrium partitioning and mass transfer relationships that control the transport of HOPs between and within highway CRM and different phases in the environment. Partitioning relationships are derived from thermodynamic principles for air, liquid, and solid phases, and they are used to determine the driving force for mass transfer. Mass transfer relationships are developed for both transport within phases, and transport between phases. Some analytical solutions for mass transfer are examined and applied to relevant problems.

Hazardous organic chemical waste that has been placed in landfills or recycled for use as highway construction and repair materials has the potential of leaching through the vadose zone into the groundwater. The groundwater may then serve as a pathway to transport these chemical contaminants to human and environmental receptors. Thus, it is important that we understand how processes that occur in groundwater affect the fate and transport of these organic chemicals. Groundwater fate and transport models are available to help us to gain this understanding, as well as to quantify the concentrations at which these organic chemicals reach receptors, so that we may be able to quantify risk.

In this chapter, we first present the physical, chemical, and biological processes that affect organic chemical fate and transport in groundwater. We also present models of these individual processes. In the second part of the chapter, we examine models that combine the individual processes, so as to comprehensively simulate how organic chemical concentrations in a contaminated groundwater system vary over space and time. Finally, we present case studies that demonstrate the utility of fate and transport modeling in helping us to understand the behavior of organic contaminants in groundwater.

The reliable assessment of hazards or risks arising from groundwater contamination problems and the design of efficient and effective techniques to mitigate these problems require the capability to predict the behavior of chemical contaminants in flowing water. To choose an appropriate remediation strategy, knowledge of the contaminant release source and time release history becomes pertinent. With more and more contamination sites being detected nowadays, it is almost impossible to perform exhaustive drilling, testing, and chemical fingerprint analysis every time, especially in the case of pollution being generated by highway construction and repair materials. Moreover, most of the time, chemical finger printing, state and federal agency records, and private parties' history records of handling hazardous substances are not sufficient to allow a unique solution for the timing of source releases. The purpose of this chapter is to present and review mathematical methods that have been developed during the past 15 years to perform hydrologic inversion and specifically to identify the contaminant source location and time-release history.

The objective of this chapter is to present some recent developments on nonaqueous phase liquid (NAPL) pool dissolution in water saturated subsurface formations. Closed form analytical solutions for transient contaminant transport resulting from the dissolution of a single component NAPL pool in three-dimensional, homogeneous porous media are presented for various shapes of source geometries. The effect of aquifer anisotropy and heterogeneity as well as the presence of dissolved humic substances on mass transfer from a NAPL pool is discussed. Furthermore, correlations, based on numerical simulations as well as available experimental data, describing the rate of interface mass transfer from single component NAPL pools in saturated subsurface formations are presented.

This chapter studies the application of chemodynamic principles to select a remediation scheme at a Louisiana Superfund site (Petro Processors, Inc (PPI) sites). The current remediation scheme at the sites, monitored natural attenuation (MNA) is a direct result of this and other research conducted at Louisiana State University. In this chapter, the results from our studies on the adsorption and desorption, the desorption kinetics, the delineation of freely desorbing and desorption resistant fractions, and the bioavailability of the desorption resistant fraction are presented along with the implication of this research for the current remediation scheme.

We observed that only a small fraction of the adsorbed mass would desorb even after a number of successive desorption steps. The investigation on laboratory contaminated soil showed a biphasic behavior, namely an easily desorbed fraction and a desorption resistant fraction. Both field contaminated and aged soils also showed the same behavior. The first stage involved a "loosely bound" fraction and the second stage involved a "tightly bound" fraction. The desorption constants calculated or estimated for the two fractions were employed to obtain the overall expected mass recovery from the contaminated zone at the site. Extremely large time frames were predicted for overall mass removal of Hexachlorobutadiene (HCBD) from the contaminated zone.

An empirical non-linear model was used to describe the bi-phasic nature of desorption with one fraction (labile) being released in relatively short periods of time (typically 24–100 h) and a second fraction (non-labile or irreversible) being resistant to desorption and the parameters estimated. In addition, desorption kinetics of three-month and five-month old contaminated soils showed that progressively less amount of contaminant was available for labile desorption (lower F) compared to freshly contaminated soil.

We observed that for freshly contaminated soil, the compound readily desorbed into the aqueous phase and was available for microbial consumption whereas for soils containing mostly the non-labile material, the contaminant availability was limited by the mass transfer into the aqueous phase. The fraction of contaminant, which is irreversibly bound to soil is typically present in micropores or chemically bound to soil humic matter and thus is not accessible for microbial utilization. These observations are in agreement with those reported for other chemicals in the literature. It is believed that the longer the contaminant age within the soil the lower the fraction of the contaminant that will be bioavailable. The observations have significant implications to the current remedy and the possibility of natural attenuation at the site.

Solidification/stabilization treatment processes immobilize hazardous constituents in the waste by changing these constituents into immobile (insoluble) forms, binding them in an immobile matrix, and/or binding them in a matrix which minimizes the material surface exposed to weathering and leaching. Solidification/stabilization treatment processes can include aluminum silicate and cement-based fixation, pozzolanic-based fixation, or vitrification.

The process of solidification/stabilization is a widely accepted treatment/disposal process for a broad range of wastes, particularly those classified as toxic or hazardous, which are not suited for normal methods of disposal and where special treatment is necessitated. Portland cement is a material found to be most useful for solidification/stabilization purposes due to its ability for heavy metals fixation and immobilization. For the immobilization of waste containing high concentrations of heavy metals, as in the case of the galvanization process, solidification is a very acceptable treatment. This is also consistent with the recent EU directions, which refereed to the solid waste management. Solidification/stabilization processes will play a more important role since, in the near future, only inert or stabilized wastes should be landfilled. Solidification/stabilization process means binding the hazardous material in the hydraulic binders for safe landfilling or use in civil engineering purposes. Various types of cement and pozzolanas (e.g., coal burning fly ash, lime, blast-furnace slag and similar materials) are mostly used as the stabilizing matrix. Those stabilization techniques are used for the immobilization of inorganic or organic waste. The end product of the treatment, usually after sufficient curing, is solid monolithic material which, depending on characteristics of leaching, can be usefully applied or disposed of in a safe way.

The issue of clean production has challenged many industries to initiate new approaches to tackle pollution problems. The traditional "end-of-pipe" treatment approach is no longer viewed as an adequate, stand-alone, pollution problem-solver. Increasing public awareness of the impact of industrial pollution, more stringent discharge standards, and escalating waste treatment and disposal costs have placed enormous pressure on industries to shift their paradigm of pollution prevention from the "end-of-pipe" treatment to waste minimization or even total elimination at the point of generation (source reduction). By reducing the energy and materials required to provide goods and services, an emerging new technology such as molecular nanotechnology (MNT) has the potential to provide more appealing products while improving environmental performance and total sustainability.

Therefore, the goals of this chapter are to: (a) provide an overview of waste minimization and its relationship to environmental sustainability; (b) portray the causes of sustainability problems and diagnose the defects of current industrial manufacturing processes in light of MNT, and; (c) analyze and extrapolate the prospect of additional capabilities that humanity may gain from the development of MNT that have the potential to ascertain total environmental sustainability.