Fate and transport processes

For convenience, we will categorize processes occurring in the groundwater as either being physicochemical or transformation processes. Of course, in reality, physicochemical and transformation processes act upon contaminants in concert. We will restrict our discussion to transport of dissolved contaminants in a porous media, as it is typically contaminants dissolved in groundwater that have the greatest potential to move from a source area to downgradient receptors. A detailed discussion of the dissolution of separate phase contaminant in the source area is reported by Chrysikopoulos [ 1 ]. 

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The facilitated transport of compounds by colloids, illustrated schematically in Figure 1.1, is important in several areas and especially in the study of the fate and transport processes of hydrophobic organic compounds and metal ions in the environment. This facilitated transport also has implications in other areas in which colloid diffusion through porous... 

Physical and Chemical Properties. Some of the physical and chemical properties (e.g., K°w Henry s law constant), often useful in estimating environmental fate and transport processes, are available for DNOC but not for other isomers of dinitrocresols (see Table 3-2). Although not as important as DNOC, it would still be useful to develop such data for other commercially available isomers of dinitrocresols. 

As with other chemical mixtures, the fate and transport processes affecting coal tar can be extremely complex. Coal tar components may partition to the air, water, soil, or biota depending on their physical and chemical properties. Compounds initially released into the atmosphere may undergo atmospheric deposition and reach surface water directly or through runoff carrying soil-bound compounds. 

If released to the environment, cyanogen chloride is expected to preferentially partition to the air, soil, and water. It is expected to slowly convert to cyanides, and will react slowly with water or water vapor to form hydrogen chloride. Photolysis may also be an important abiotic removal process. Bioconcentration and bioaccumulation potential is expected to be low. Volatilization is expected to be an important fate and transport process based on the vapor pressure. Cyanogen chloride is expected to persist in air if released. 

If released to the environment from natural or anthropogenic sources, ethanol is expected to preferentially partition to the soil, water, and air. Bioconcentration and bioaccumulation potential is expected to be low, based on the estimated bioconcentration factor and experimental octanol water partition coefficient. If released into water, it is expected to have a half-life of less than 10 days. When released into the air, it is expected to have a half-life of less than 5 days, and is expected to be removed from the air by wet deposition. Biodegradation and volatilization are expected to be important fate and transport processes for ethanol. 

Before discussing in detail any of the fate and transport processes occurring in surface waters, the major characteristics of surface waters must be defined. As illustrated in Fig. 2-1, rivers and streams are relatively long, shallow, narrow water bodies characterized by a pronounced horizontal movement of water in the downstream direction. Often the water flow is sufficiently turbulent to erode the stream channel and carry sediment for considerable distances. Due to this movement of sediment, some river channels are constantly shifting in geometry. Compared with rivers, lakes tend to be deeper and wider and are not dominated by a persistent downstream current (Fig. 2-2). Lakes are often vertically stratified for part of the year, with two distinct layers of water whose temperatures and chemistries are markedly different. Estuaries (Fig. 2-3), the interfaces between rivers and the ocean, also are often vertically stratified, due to the denser saline seawater sinking beneath the freshwater discharged from the river. Estuaries have tides due to their connection to the ocean, and they tend to be rich in nutrients. 

It is extremely difficult to make general statements about typical TPH or TPH-component levels in environmental media. Environmental fate and transport processes of TPH mixtures are complex. Interactions of the chemicals within the bulk oil typically result in different environmental fate and transport than would be predicted for the individual components. As with the discussion of basic fate and transport processes (see in Section 5.3), site-specific information is nearly always needed for... 

This is a handbook on containment of ground water contamination. In situ treatment, and contaminant removal. It discusses subsurface fate and transport processes, ground water and contaminated soils bioremediation, ground water pump-and-treat technologies. soil vapor extraction, and multiphase contamination and free product recovery. 

Brannon JM and Pennington JC, Environmental Fate and Transport Process Descriptors for Explosives, ERDC/EL TR-02-10, Engineer Research and Development Center, prepared for US Army Corps of Engineers, Washington, DC, 2002. 

Successful modeling of 2,3,7,8-TCDD photolysis in soils requires additional basic information on the significance of photolysis in relation to other fate and transport processes. 

The Level III model includes all the important fate and transport processes in a real environment and is one step more complex than Level n. As in the Level II model, the chemical is discharged at a constant rate into the environment to reach a steady state (at which input equals output). Unlike Level II, equilibrium between different media is not assumed and rates of chemical transfer by intermedia transport processes are defined. The individual discharges to all environmental media must be specified because fhe disfribufion of the chemical between media now depends on how the chemical enters the system. Depending on the properties of a chemical, the mode of entry can also significantly alter chemical persistence or residence time in the environment to viues that are quite different from Level II results. A series of 12 transport velocities control chemical transfer between the four primary environmental media (air, water, soil, and sediment). Equilibrium is assumed, however, within each medium. For example, suspended matter and fish are assumed to be at the same fugacity as water. 

We come back to this concept of mass balance after examining some of the most important fate and transport processes that affect a mass balance. 

Surface water flow may transporf microbeads until they degrade, are ingested by organisms, wash up on a shoreline, or perhaps, come to rest in sediments. Those fate and transport processes are described briefly below the potential for organisms to ingesf microbeads is discussed in Ihe overview of (eco)toxicological concerns. 

Chapter 5 comprises fate and transport processes for environmental lead. These processes enter into and underpin the environmental cycling of the element and the contaminant s appearance in various media encountered by human populations. 

Lead in the Human Environment Fate and Transport Processes... 

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