Environmental Engineering Reference
In-Depth Information
Chapter 22
Natural Attenuation
Anita Peter, Thomas Held, Norbert Hüsers, and Frank A. Swartjes
Abstract
Natural Attenuation (NA) has emerged during the last 10-15 years
as a useful and cost-efficient alternative approach for contaminated site man-
agement. It refers to the naturally occurring processes like dispersion, diffusion,
sorption, volatilization, degradation and transformation, all of which can substan-
tially decrease contaminant concentration, mass, toxicity and/or mobility within
soil and groundwater. The efficiency of Natural Attenuation processes depends to
a large extent on site-specific conditions, primarily on the type of contaminants
present at the site. Proving and evaluating the efficiency of Natural Attenuation pro-
cesses is a prerequisite for accepting them as the sole or additional remediation
alternative. The implementation of Natural Attenuation as a remediation alterna-
tive, i.e. the monitoring that assures sustainability of Natural Attenuation processes
over time, is called Monitored Natural Attenuation (MNA). This chapter presents
an overview of the history and political acceptance of Natural Attenuation and the
principles on which it was built. Specifically, it describes how the different pro-
cesses act on contaminant plume development and explores methods of evaluating
Natural Attenuation processes and proving their effectiveness. A stepwise approach
to assess and implement Natural Attenuation is presented, followed by three sec-
tions on the most frequently found contaminant groups for which Monitored Natural
Attenuation is being applied. These are petroleum hydrocarbons, chlorinated hydro-
carbons and tar oil contaminants. Characteristics of these contaminant groups, the
resulting contaminant-specific potential for implementation of Natural Attenuation
and the challenges to be expected, are elucidated and discussed.
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