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Permeable Reactive Barriers in Europe
groundwater plume; hence, a continuously contaminated area upstream of
the barrier is tolerated. The section downstream the barrier is affected by
the cleanup effect of the barrier, and hence shows decreasing and eventually vanishing contaminant concentrations over time. PRBs are therefore
chiefly regarded as protective measures for safeguarding communities and
environments that would otherwise be exposed to the contaminant source,
or in other words, jeopardized by contaminated groundwater discharging
from the source in a certain distance downstream. In cases where the source
becomes entirely depleted over the operational term of the PRB, the barrier may achieve an actual decontamination over time. Thus, PRBs can be
regarded as both a safeguarding technique and as an actual decontamination technique, depending on the contamination scenario and its outcome
during the barrier’s operational life.
In summary, PRBs are not designed for swift remedial action of the
source zone. They are designed for managing a source zone by eliminating
the plume over a long period of time, accepting that the original source
of the contamination and the upper part of its discharging plume are not
tackled. The operational lifetime of a PRB may thus range from years to
decades.
Two definitions for PRBs were issued in the United States in 2000 and in
the United Kingdom in 2002, respectively. A German definition, being similar to that of the United Kingdom, was published in 2006 (Burmeier et al.,
2006).
The U.S. EPA defines PRBs as follows: A PRB is an emplacement of reactive
materials in the subsurface designed to intercept a contaminant plume, provide a flow path through the reactive media, and transform the contaminant(s)
into environmentally acceptable forms to attain remediation concentration
goals downgradient of the barrier (Gavaskar et al., 2000).
The U.K. Environment Agency defines PRBs as follows: A PRB is an engineered
treatment zone of reactive material(s) that is placed in the subsurface to remediate contaminated fluids as they flow through it. A PRB has a negligible
overall effect on bulk fluid flow rates in the subsurface strata, which is typically achieved by construction of a permeable reactive zone, or by construction of a permeable reactive “cell” bounded by low permeability barriers that
direct the contaminant toward the zone of reactive media.
The emplacement of columns of reactive media, such as modified clays
using soil-mixing techniques is not considered a PRB unless it is adequately
demonstrated that the permeability of the mixed columns is not significantly
less than that of the soil prior to mixing. Low permeability clay barriers that
provide a degree of attenuation (typically sorption of contaminants to the
clay minerals) are excluded from the definition of PRBs.
Permeable Reactive Barriers in Europe
groundwater plume; hence, a continuously contaminated area upstream of
the barrier is tolerated. The section downstream the barrier is affected by
the cleanup effect of the barrier, and hence shows decreasing and eventually vanishing contaminant concentrations over time. PRBs are therefore
chiefly regarded as protective measures for safeguarding communities and
environments that would otherwise be exposed to the contaminant source,
or in other words, jeopardized by contaminated groundwater discharging
from the source in a certain distance downstream. In cases where the source
becomes entirely depleted over the operational term of the PRB, the barrier may achieve an actual decontamination over time. Thus, PRBs can be
regarded as both a safeguarding technique and as an actual decontamination technique, depending on the contamination scenario and its outcome
during the barrier’s operational life.
In summary, PRBs are not designed for swift remedial action of the
source zone. They are designed for managing a source zone by eliminating
the plume over a long period of time, accepting that the original source
of the contamination and the upper part of its discharging plume are not
tackled. The operational lifetime of a PRB may thus range from years to
decades.
Two definitions for PRBs were issued in the United States in 2000 and in
the United Kingdom in 2002, respectively. A German definition, being similar to that of the United Kingdom, was published in 2006 (Burmeier et al.,
2006).
The U.S. EPA defines PRBs as follows: A PRB is an emplacement of reactive
materials in the subsurface designed to intercept a contaminant plume, provide a flow path through the reactive media, and transform the contaminant(s)
into environmentally acceptable forms to attain remediation concentration
goals downgradient of the barrier (Gavaskar et al., 2000).
The U.K. Environment Agency defines PRBs as follows: A PRB is an engineered
treatment zone of reactive material(s) that is placed in the subsurface to remediate contaminated fluids as they flow through it. A PRB has a negligible
overall effect on bulk fluid flow rates in the subsurface strata, which is typically achieved by construction of a permeable reactive zone, or by construction of a permeable reactive “cell” bounded by low permeability barriers that
direct the contaminant toward the zone of reactive media.
The emplacement of columns of reactive media, such as modified clays
using soil-mixing techniques is not considered a PRB unless it is adequately
demonstrated that the permeability of the mixed columns is not significantly
less than that of the soil prior to mixing. Low permeability clay barriers that
provide a degree of attenuation (typically sorption of contaminants to the
clay minerals) are excluded from the definition of PRBs.