environment

Ingeokring Newsletter
are available to do so. Repairing a leak in a traditional
way however is expensive and sometimes even
impossible because the locations of leaks are hardly
accessible for big and heavy equipment. The available
methods to repair the leak in situ so far (for example
injection of grouts and gels) have numerous
disadvantages. They are often expensive and
environmentally unfriendly. Another disadvantage is
that an excessive amount of injection fluids is required
because the location of the leak is not exactly known.
Therefore, a need exists for easier, more effective and
less expensive methods.
2. BioSealing: a new promising solution
The method of BioSealing utilises the natural chemical,
physical and biological properties of the soil, the
groundwater and the leak itself. The idea of BioSealing
evolved from problems occurring in the field of drinking
water supply, namely clogging in groundwater extraction
wells. In groundwater extraction more or less the
opposite of the problem of leak occurs: near
groundwater extraction wells clogging takes place which
puts limits on the possible amounts of extraction and
causes many problems. These clogging processes are
caused by natural processes in the underground. The
idea of BioSealing was to use and stimulate these natural
clogging processes to repair leaks in water barriers by
adding nutrition. In the case of BioSealing repair of leaks
is interpreted as “to reduce the permeability at the
location of the leak”. One of the goals set when this
method was designed was to reduce the permeability
with at least a factor 5.
Due to a difference in hydraulic heads inside and outside
the water retaining barrier a groundwater flow is induced
towards and through the leak. Addition of nutrition for
micro-organisms near the leak creates a favourable
environment which leads to a multiplication of microorganisms
in the vicinity of the leak. The microorganisms
will cause a biological clogging of biomass
in the leak. Later this clogging can be reinforced by a
(biologically induced) chemical precipitation of iron sulphide.
The method of Bio Sealing has been patented by
GeoDelft.
3. Laboratory testing
Set up
In a first stage the BioSealing process was tested in a
laboratory setting. The objective of the laboratory test
was to discover if it was possible to control the clogging
process in a defined environment In large PVC columns
filled with natural Dutch Pleistocene sand a separation
plate with small hole was placed, representing a leak,
while water was squeezed through the columns under
constant pressure. The nutrition (Nutrolase provided
by AVEBE) was added to the water to stimulate bacterial
growth and thereby close the leak. The location of the
clogging process and the durability of the clog were
studied.
The experiments were performed under anaerobic
conditions using the water as transport medium for
nutrition. The water flow was directed towards and
through the leak. The water flow was driven by natural
decline in the column (using a storage tank) and the
flow was upwards to prevent specific flow channels to
occur. Two inlets were created, one for water and one
for the nutrition (Nutrolase) was created. Groundwater
velocities used were based on travel time between
injection and hole in real conditions. This time was
estimated for building pits using customary
groundwater conditions, knowledge of leaking
conditions and the knowledge that new leak detection
techniques can find the leak within 5 meters accuracy.
This accuracy is realistic with electrical leak detection
techniques such as ECR and EFT, recently tested on
several sites in the Netherlands and Germany.
Results
From these experiments it was concluded that it is
possible to repair a leak with natural clogging processes.
In the laboratory experiments the clogging always
appeared around the leak, independently of the flow
speed, the size of the leak and the kind of nutrition. The
experiments showed some difficulties. An example of a
difficulty encountered was the formation of gas that
causes temporary clogging. After the gas has
disappeared the leak flow is reinstalled. The gas
formation may be caused by high temperature in
laboratory circumstances. The durability tests showed
that after stopping the nutrition supply the microorganisms
stayed at the hole for the duration of the
test, which was in this case 4 months. This leads to the
conclusion that Bio Sealing is a durable solution. A
boundary condition is that the clogging process takes
place in an anaerobic environment, because otherwise
the iron sulphide will oxidate and dissolve.
Figure 2: Set up of the field experiment
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