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Natural attenuation (intrinsic remediation) relies on physical and biological processes that reduce the
concentration of subsurface contaminants without artificial enhancement. Biodegradation is one of the
processes which offers potential for mass removal and contaminant destruction. Under highly reducing conditions,
anaerobic microbes transform trichloroethene (TCE), a chlorinated solvent, through successive removal of chlorine
atoms to cis-1,2-dichloroethene (DCE), vinyl chloride (VC), and ethene. As DCE and VC increase in concentrations,
TCE concentrations decrease.
As mandated by Ohio EPA, ground water at an industrial site has been monitored since 1991.
Figure 1
shows yearly average concentrations over time of TCE, DCE, VC, and ethene in micrograms per liter (µg/L).
Increases and subsequent decreases of DCE concentrations, followed by increases of VC concentrations, are evident.
TCE concentrations are relatively low, ranging from less than 1 to 9 (µg/L).
Figure 2
shows concentrations over time converted to micromoles per liter. Increases and subsequent decreases of DCE,
followed by increases of VC and ethene, are more clearly depicted.
Figure 3
shows micromolar fractions of TCE and its degradation products.
This graphic illustrates the relative reduction in TCE concentration. A natural attenuation remedy is proposed
for this site. This is an example of one of the tools Environmental Design Group may use to convince agencies
that TCE remediation is occurring in a timely manner.
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