environment

Ingeokring Newsletter
ENVIRONMENT
Permeable Reactive Barriers as an interesting
alternative to Isolation, Maintenance and Control
W.H. van der Zon & J. Maccabiani, GeoDelft, Delft, email: w.h.vanderzon@geodelft.nl
Introduction
Permeable reactive barriers have been the subject of
research in the Netherlands, but few have actually been
implemented. This short paper describes the route from
research to implementation of a permeable reactive
barrier.
A Permeable Reactive Barrier (PRB) is a frequently used
method of removing groundwater contamination in the
USA and Canada [EPA 2002]. A PRB is a screen that
contains or creates a reactive treatment zone that aims
to intercept and remediate a contaminant plume (see
figure 1). This is a way of passively remove contaminants
from the groundwater by physical, chemical or biological
processes. Some PRBs are installed as a permanent
system and some have removable in-situ reactors which
can be renewed with a cassette-like system.
Case: fluorides & cyanides in a landfill leachate
To give a short view of the route from research to
implementation we will discuss a case in which the
groundwater is contaminated with fluorides and
cyanides. The problem site has been used in the 60’s
and 70’s to dump both industrial as well as household
waste. It was closed in the early 80’s. At present the site
is in use as both a motocross racetrack and it houses
the practice grounds of a rifle association.
The leachate from the site contains both fluorides (in
high concentrations) and cyanides. The contamination
plume has to be dealt with in order to prevent further
contamination of groundwater outside the site’s limits.
The default approach to such a problem is a “total
remediation strategy”, meaning that activities are aimed
at actively removing all the contaminants from both the
ground and the groundwater. This would mean however
that the site cannot be used for human activities other
than the clean-up for quite a while. Both present users
of the site, the motocross club and the rifle club, are
difficult to relocate. Therefore the current use of the
site demands a special approach.
The objectives to look for a new remediation strategy
are:
1. Present users of the site must be able to keep
using it throughout the remediation. Therefore
remediation must take place in situ;
2. The remediation concept should take care of the
existing plume, it has to be thorough;
Figure 1: sketch showing the principle of groundwater
cleanup using PRBs [EPA2002]
3. The costs of the remediation must be lower than
the conventional method of isolation,
maintenance and control, “IMC” (or else this,
rather expensive, strategy should be used).
The idea was born to use a PRB. Since PRBs clean up
contaminations in the ground water in-situ, the site can
still be used for it’s present functions. The costs of
PRBs are generally, and also in this case, much less
than when using an IMC method. A PRB would fulfill all
objectives if it could be proven that objective 2 can be
fulfilled. A pilot project was then defined to investigate
if a PRB can thoroughly clean the groundwater
contamination.
Design points of interest
The design process will not be discussed here, but
several important points of interest are named. For this
case, the design of a PRB for this site consisted of
exploring:
1. the contaminated site itself, including:
• assessments of the representative type of
groundwater
• assessments of the representative contamination
(e.g. heavy metals, VOCl’s, fluorides & cyanides)
2. the geotechnical boundary conditions
(especially grain size distributions for the
permeability profile)
3. the geochemical boundary conditions (reaction
rates, competing reactions)
4. the geohydrological conditions, especially the
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