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| Resource Library > Technology Transfer > Programs and Initiatives > Monitored Natural Attenuation > Design |
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Several techniques are available for evaluating
and quantifying natural attenuation at field sites. The most commonly used
techniques involve an evaluation of plume stability and mass loss and approximating
the importance of biodegradation using contaminant and geochemical data. These
have been termed
lines of evidence for evaluating natural attenuation. Plume
stability refers to the size of the contaminant plume over time. As biological
degradation continues to remove dissolved contaminant the size of the plume
will stabilize or shrink. Dissolved-phase concentrations of contaminants will
also decline. Concentrations of electron acceptors, such as dissolved oxygen
and nitrate, will become depleted as petroleum hydrocarbons are biodegraded.
During the reductive dechlorination of CAH the groundwater environment will
become reducing and daughter products of the process may be detected. These
lines of evidence are discussed fully in the AFCEE protocols. Additional techniques
that can be used to assess natural attenuation include biodegradation rate constant
calculations and groundwater flow and solute transport models. In rare cases,
microbiological laboratory data can be used to evaluate biological processes.
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