Chlorinated solvent plume

BIOCHLOR A natural attenuation model for chlorinated solvent plumes ... 

Natural attenuation processes affecting chlorinated solvent plumes.1572... 

Chlorinated solvent plumes-case smdies of natural attenuation.1602... 

This chapter is focused on the natural attenuation behavior of CS at the field scale. The first part of the chapter reviews many of the physical, chemical and abiotic natural attenuation processes that attenuate CS concentrations in ground water. Some of these processes have been described in more detail in previous chapters in the handbook and are therefore only reviewed in brief In the second part of this chapter, we will review the biological processes that bring about the degradation of the most common chlorinated solvents, present conceptual models of chlorinated solvent plumes, and summarize data from field studies with chlorinated solvent contamination. 

NATURAL ATTENUATION PROCESSES AFFECTING CHLORINATED SOLVENT PLUMES... 

At many chlorinated ethene sites, concentrations of cis-1,2-DCE are often higher than any of the parent chlorinated ethene compounds. The reason for the accumulation of 1,2-DCE may be due to either slower rates of DCE halorespiration, or the prevalence of organisms that reduce PCE as far as cis-1,2-DCE over ones that can reduce PCE all the way to ethene. Although many researchers have commented that reductive dechlorination will result in the accumulation of VC (e.g., see 84, 89), at many field sites VC accumulation is much lower than cis-1,2-DCE. This may occur because the vinyl chloride in many chlorinated solvent plumes can migrate to zones that can support direct oxidation of VC oxidation, either aerobically and/or anaerobically. 

Wiedemeier et al. proposed a classification system for chlorinated solvent plumes based on the amount and origin of fermentation substrates that produce the hydrogen that drives halorespiration. Three types of groundwater environments and associated plume behavior, Type 1, Type 2, and Type 3, are described below. While the classification system can be used to represent entire plumes, it can also be used to define different zones within a chlorinated solvent plume. 

Figure 23.1.6. Conceptual model of Type 1 environment for chlorinated solvent plumes. [From T.H. Wiedemeier, H. S. Rifai, C. J. Newell and J.T. Wilson, Natural Attenuation of Fuels and Chlorinated Solvents in the Subsurface, after reference 88. Copyright 1999 John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.]...

As mentioned above, a single chlorinated solvent plume can exhibit different types of behavior in different portions of the plume. This can be beneficial for natural biodegradation of chlorinated solvent plumes. For natural attenuation, this may be the best scenario. PCE, TCE, and DCE are reductively dechlorinated with accumulation of VC near the source area (Type 1) then, VC is oxidized (Type 3) to carbon dioxide, either aerobically or via Fe(III) reduction further downgradient and does not accumulate. Vinyl chloride is removed from the system much faster under diese conditions than under reducing conditions. 

Table 23.1.10. Characteristics of chlorinated solvent plumes from HGDB database...

---