environment

Vol. 11 No. 1 2004
Figure 3: Groundwater flow data
4. Field Experiment
In the beginning of 2004 a field experiment was designed
because the circumstances in the laboratory (for example
temperature, scale, heterogeneity, size of the leak) are
different from the circumstances in the field. The objective
of the field experiment is to see whether a reduction
of the permeability at the location of the leak with a
factor 5 is feasible. In the design representation,
inspection of unwanted leak, costs and possibilities to
monitor were factors that played an important role.
The experiment is currently carried out at the factory
site of Lyondell Chemicals Nederland B.V. at the
Maasvlakte (port of Rotterdam). This location has been
selected because of the presence of sandy subsoil, the
presence of groundwater at reachable depth and the
relationship with Lyondell due to geotechnical soil
investigations in the past. Figure 2 shows a schematic
drawing of the experimental setting. The experiment is
carried out by using three 20ft sea containers, which
are buried with the doors at the top (so 90 degrees
rotated). To avoid the influence of oxygen in the
anaerobic process of reducing the permeability in the
vicinity of the leak, it is necessary to have at least one
meter groundwater above the bottom in the container.
The difference in hydraulic head (3 to 4 meters under
normal circumstances) is being maintained by a
horizontal drain in combination with a pump. The drain
has been constructed in a gravel filter to avoid clogging
near the drain. The fact is that the circumstances nearby
the injection point are similar to those nearby the leak:
streamlines come together and the flow rate increases.
It is therefore not unrealistic that when the permeability
nearby the leakage reduces, this also happens nearby
the drain, which is an unwanted side effect. The large
porosity of the gravel filter has to avoid this potential
problem of clogging.
To stimulate the micro-organism activity, Nutrolase is
injected at various places and various depths by using
an injection method similar to grouting. It is generally
known that by injection of nutrition clogging may occur
near the injection point. During the experiment, after
injecting nutrition water is injected to clean out the
immediate vicinity in order to prevent clogging. Also
the possibility exists to inject the nutrition under high
pressure to be able to reduce the amount of clogs near
the injection point. During the experiment nutrition is
injected several times to reach maximum micro-organism
activity.
The process is monitored by standpipes, a water meter
and several apparatuses to measure chemical properties
of ground water (pH, EC, oxygen, redox potential). A
decreasing redox potential indicates for example an
increasing micro-organism activity and a decreasing flow
indicates a decreasing permeability nearby the leak. A
monitoring plan was designed to collect more
information about the behaviour of the nutrition and
micro-organisms in field conditions. Also it provided a
possibility to be able to make adjustments in the
parameters that can be influenced in case of unforeseen
developments.
At the moment of writing the flow has decreased by a
factor three, so the target of a decrease by a factor five
is not reached yet. In figure 3 the change of the flow in
relation to time is shown. Vertical lines represent the
dates of injection of nutrition. The decline in the flow
between February 20 2004 and February 25 2004 is
caused by setting the stationary head and is therefore
not relevant in relation to the clogging.
5. Discussion
Although the field experiments are not completely
finished yet, BioSealing will provide both the field of
civil engineering and environmental geotechnics with a
sustainable method for decreasing permeability of the
soil, which will be useful for the repair of leaks. The
solution is sustainable because use is made of natural
micro-organisms and natural occurring physical,
chemical and biological processes that are stimulated
11