The basic principal of all geoelectrical leak location
methods is to pass an electrical current through any
faults present in the geomembrane, generating electrical
signals that can be detected by a qualified operator.
Whilst the importance of site preparation is well known
for dipole method surveys, it is also a key element of a
successful water puddle survey.
Electrical isolation is much easier to achieve when the
survey site is an independent system distinct from its
surrounding environment. However, leak location is often
required on extension systems of sites that are currently
operational. From a leak location standpoint, the ideal
survey cell would be fitted with a liquid collection
system at its lowest point with the walls of the cell
rising gently toward its extension cells. But even in
these cases, the leak location operator should be careful
to minimise the volume of water used whilst validating the
joins (tie-ins) between the cell and its extensions to
ensure that background noise is kept to a minimum.
Additionally, a significant rainfall event can saturate
the operational sector causing water (and even leachate)
to accumulate in the survey area. In such cases, the only
option is to pump water from the survey area and allow the
geomembrane surface to dry out, ensuring that the water
used during the survey remains isolated from the active
systems. This phenomenon is particularly common when the
survey site’s low point is located at a join between two
systems, allowing for water to accumulate above the join.
In such cases, the only recommendation is to start the
survey at the low point using a minimum of water, and to
perform the survey moving away from the low point
sufficiently quickly to avoid survey water reaching water
accumulating at the low point.
Occasionally the geomembrane layer of the survey site is
exposed at the walls and covered at the base. If leak
location is required on the exposed walls, methods which
do not use water should be prioritised in order to avoid
excessive background noise as survey water reaches the
base’s covering layer, especially where this layer is not
isolated (in the case of an access road, for example). A
similar situation arises when survey water enters into
contact with a saturated covering layer, with any leak
present in the liner beneath the covering layer causing
false positives during the wall survey.