environment

Vol. 11 No. 1 2004
Figure 2: Fundamental difference between "funnel and gate" systems (left) and "continuous trench" systems (right).
[EPA 2002].
direction of flow and flow velocity of the
groundwater
5. suitable barrier materials and type of remediation
process (chemical adsorption, physical
adsorption)
6. the effectivity of the physical or chemical
process through implementation and interpretation
of laboratory studies and numerical models
Resulting design of the PRB
The design process mentioned above resulted in a
design with a barrier based on two materials, zeolite and
iron. They are used in a “funnel and gate” type
barrier for capturing fluoride and cyanide. The funnel
and gate design efficiently catches the ground water
flow and forces it to flow through the reactive barrier
(see figure 2).
In figure 3, the design of the PRB is shown. The drain at
the bottom of the PRB is there to collect some of the
leachate after it went through the reactive barrier. With
this drain it is easy to carry out quality control. During
a pilot project the level of remediation of the polluted
ground water has been analysed against several easily
measurable macro parameters. It was found that these
macro parameters give detailed information about the
level of remediation inside the reactive barrier. This
makes quality control an easy job which can be
performed from behind the desk – no (expensive)
laboratory work is necessary.
The drain can also have the function of a hydrological
barrier, preventing the contaminated ground water in
case the reactive barrier will fail (for one reason or
another). As such, the system is called “fail-safe” with
a double isolation system.
By lowering the groundwater table inside the waste
disposal site a continuous flow is created towards the
reactive barrier. This effect can be made to just include
all (probable) contaminated areas, also the ones just
outside the site’s perimeter. In this way the “outer
regions” will be cleaned as well.
The costs of this PRB system are estimated at only 20
% of the costs of the conventional method of isolation,
maintenance and control. Therefore the PRB can be
seriously considered as an interesting alternative for
the isolation, maintenance and control.
References
U.S. Environmental Protection Agency (EPA), (2002),
“Field applications of in situ remediation
technologies: permeable reactive barriers”, EPA office
of solid waste and emergency response technology
innovation office, Washington, dc 20460
Figure 3: The design of the PRB
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