Environmental Engineering Reference
In-Depth Information
extraction from the groundwater or porewater is required. It is not unusual to remove some
large proportion of the contaminants from the groundwater or porewater, and to leave the
remaining proportion to be removed via natural attenuation processes in an IRR.
3.4.1.9 Permeable Reactive Barriers
The intent of a permeable reactive barrier is to provide treatment as a remediation proce-
dure to a contaminant plume as it is transported through the PRB so that the plume no
longer poses a threat to biotic receptors when it exits the PRB. Figure 3.13 shows a funnel
and gate arrangement of a PRB application where the contaminant plume is channeled to
the PRB gate by the impermeable walls. Transport of the contaminant plume through the
PRB allows the various assimilative and biodegradative mechanisms of the treatment wall
to attenuate the contaminants. The PRB needs to be strategically located down-gradient to
intercept the contaminants.
PRB are also known as treatment walls. The soil materials in these walls or barriers can
include a range of oxidants and reductants, chelating agents, catalysts, microorganisms,
zero-valent metals, zeolite, reactive clays, ferrous hydroxides, carbonates, and sulfates, fer-
ric oxides and oxyhydroxides, activated carbon and alumina, nutrients, phosphates, and
soil organic materials. The choice of any of these treatment materials is made on the basis
of site-speciic knowledge of the interaction processes between the target contaminants
and material in the PRB. Rapid clogging or deactivation of the material must be avoided.
Site geology, geochemistry, and microbiology, in addition to contaminant concentrations
Plan view of funnel and treatment gate
Impermeable
funnel wall
Treatment wall thickness allows contaminants'
residence time for interactions to achieve
effective attenuation
Hydraulic conductivity of wall
should be greater than the
surrounding material.
�is means that the
permeability of the material in
the wall must be greater than
that of the surrounding soil.
Contaminant
plume
Plume leaving treatment
wall should be “clean”
Treatment wall
(high permeability reactive barrier)
Impermeable walls funneling pollutant plume
to treatment wall
FIGURE 3.13
Funnel and gate arrangement of PRB treatment of contaminant plume. Funnel effect is provided by the imper-
meable walls that channel contaminant plume transport to the PRB gate. (From Yong, R.N. and Mulligan, C.N.,
Natural Attenuation of Contaminants in Soils , CRC Press, Boca Raton, 310 pp., 2004.)
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