Inventors of electronic geomembrane leak detection and location systems.

Electronic geomembrane leak detection and location is a powerful tool, used to monitor waterproofing and containment systems first ensuring an effective seal is created and then that it is maintained.

The detection and location of leaks electronically is equally useful for the protection of leaks out of containment or storage facilities as it is to the prevention of leaks into structures that house sensitive contents, or even to protect flat roofs from leaks in to prevent damage to expensive finishes.

The market leading leak location systems developed by Sensor are used to test geomembranes and roofs for integrity, our monitoring systems provide warnings automatically the moment penetrative damage occurs thus preventing any significant leaks and mitigating the potential for periods of sustained percolation along with the minimisation of consequential damage that can occur as a result.

Sensor systems are designed to protect clients, contractors and insurance companies alike, our vast experience in the discovery of geomembrane and roofing membrane failure enables us to anticipate when and where damage will occur. In turn this means we can target the development of our systems at capturing and repairing damage at each stage in the installation and subsequent life of the membrane.

Our systems locate and detect leaks as they occur meaning that rectification is a small scale, low cost and highly targeted process instead of a complete or partial replacement project because Sensor DDS® demonstrates geomembrane integrity in realtime. This means that for dirty applications (e.g. waste, mining, oil and gas extraction) there is an improved chance of success with regulatory compliance and approval at the planning stage.

For clean installations such as potable water prevention of bacterial / chemical ingress can be pro-actively prevented whether this is due to accidental or, criminal damage.

During your membrane's service life electronic leak detection can prove your facility is not leaking, minimise any repair costs and mitigate the volume of any leaks when geomembrane damage occurs as well as minimising any consequential damage as result of a leak.

Electronic leak detection technologies provide a robust solution to ensure that leaks through waterproofing system are eliminated from roofs, tanks, landfill sites, ponds, secondary containment systems and lagoons no matter what they contain.

How Does Geomembrane Leak Detection Work?

The basic concept of geomembrane leak detection is to exploit the non-conductive nature of plastic membranes, which do not allow the transmission of electrical signals unless damage is present, in which case the electrical signal will follow moisture through the damage. By measuring for the presence of electrical signals that are injected into the ground above and below the geomembrane it is possible to not only detect that damage exists but also to map the position of such damage.

The principal is very simple and works perfectly in laboratory conditions, in the field there are some significant challenges that require experience, know how and research to overcome. Some examples of common issues are:

• Edge Effect
• Boundary Condition
• Background Signal

Edge effect occurs around the perimeter of an installation and it occurs because at this position the electrical resistivity of any hole in the geomembrane is higher the than the resistivity of the electrical path around the edge of the geomembrane. Ohms Law dictates the electrons will simply take the path of least resistance, which is therefore not necessarily through the hole.

Boundary condition is a phenomenon whereby one instance of damage can electrically disguise another nearby hole.

Background signals from local geological conditions, mobile telephone masts, generators, buried electrical cables and other electromagnetic interference can distort the positioning of damage or even provide for false positive readings as to the existence of damage itself.

Sensor have developed procedures, designs and systems to help mitigate the technological limitations of electronic leak detection and location but still the most important criteria is experience when it comes to successfully delivering a 100% leak free installation to our clients.

The History of Electronic Leak Detection and Location Systems

Systems first started to appear in Europe and America simultaneously in the 1980's. In the USA the mobile survey technique was developed for finding holes in covered geomembranes whilst the water lance and water puddle methods, also developed there for exposed geomembrane testing.

At the same time in Europe the 'Fixed Leak Detection System' was developed along with a mobile survey system, later a waterless Arc Testing system was also developed for the testing of exposed liners.

It was soon discovered that the most economic solution to any geomembrane testing regime was to employ multiple testing techniques. This is because the vast proportion of damage that occurs to a geomembrane is paradoxically as a result of the installation of the protective layer installed on top. Research has shown that 85% of damage to geomembranes occurs as a result of following trades whereas only 15% could be attributed to workmanship, handling, storage and manufacturing faults.

In order to cost effectively repair geomembranes best practice was established as a two stage process. Firstly testing of the exposed liner and then secondly to retest the liner once it is covered. The testing of the exposed liner eliminates any faults, accidental damage or workmanship issues and whilst these represent a minority of global damage causation, it is still more cost effective to repair these while the installer is on site and without having to dig off the covering layer. The exposed liner test therefore reduces the amount of digging necessary to carry out all repairs that will be necessary on a site. The saving in cost of digging and remobilisation of the lining installer easily offsets the cost of the exposed liner testing.

Once the liner is covered it can then either be tested, repaired and certified intact by using Mobile Survey techniques or if installed the Fixed System.

Why is Geomembrane Testing Necessary?

Whether your structure is a lagoon, pond, or lake for storing product, waste or solely for decorative purposes; or even if it is a roof for keeping out moisture or contaminants, the most common response we hear in response to the proposal to use geomembrane integrity testing, is: "What's the point? We have a warranty or guarantee from the installer / manufacturer!"

Of course building warranties can be important, but when you are suffering the consequences of a leak, particularly in commercial circumstances you will want it resolving as fast as possible in order to mitigate any losses that you might incur as a result of leakage. We have seen brand new shopping centres with leaking roofs causing tenant vacation and anaerobic digesters vital to the running of a manufacturing plant causing the halting of production at literally enormous cost. Such consequential losses are often excluded by warranty wordings and therefore have to be borne by the client in any event.

Another issue that should be considered is that if the damage is caused by a 3rd party such as a maintenance crew, or following trade a roof or liner specific warranty is worthless because it will certainly not cover accidental damage. Serious consideration should be given to the fact that 85% of damage to membranes / liners is caused by following trades and maintenance crews therefore only 15% of the damage to liners / membranes is attributable to a warranty if the company that issued it is even in business by the time you come to call upon it.

The unique benefits of leak detection in mitigation of consequently losses are brought about by being able to immediately identify damage has occurred and then being able to accurately locate the position of damage so that it can rapidly repaired without significant disruption or large scale replacement.

The Variants of Geomembrane Leak Detection Systems in Use Today

Following the early development of leak location systems set out in our historical account, the same basic categorisation of systems still remains in place today:

EXPOSED GEOMEMBRANE TESTING

Water Puddle / Water Lance Method

These methods use water charged with electricity to find damage where the signal can effectively find earth through a hole. The process is effective but is not sensitive to very small damage where lack of pressure to force the water through a hole can mean that small holes are easily missed.

There is also a common misconception that water based electronic leak detection can be used in wet climates successfully, however our experience is that in common with Ohms Law and in similarity to Edge Effect described above if water is covering everything due to the rain then it very unlikely that signal will travel through a hole, instead it will find earth by the path of least resistance (not necessarily through damage).

A disadvantage with this method is the need for significant quantities of water which can be a problem on remote sites where water might have to shipped in by tankers.

Arc Test Method

The arc test method is a waterless testing method that can find perforations in geomembranes that are less than a pinhole in size it is in our view the most effective and accurate way to find holes in exposed geomembrane.

The process similarly to other exposed geomembrane testing systems cannot be carried out in wet conditions.

A distinct advantage of Arc Testing is that the equipment is light and simple to use and does not require complicated arrangements of hoses connectors and water pumps. In addition being a dry method in a lagoon environment it does not cause complications through introducing water that then needs to be removed in order to carry out primary liner installations on double lined solutions, or for example where the basal area of lagoon is needed to fabricate a floating cover.

COVERED GEOMEMBRANE TESTING

Mobile systems

Mobile or walk over systems employ sensors that carried over the surface of the covered geomembrane, measurements are taken in a regular grid fashion often 1m x 1m. Before commencing measurement a special transmitter is used to deliver a predefined signal with opposite poles being placed on either side of the geomembrane installation (e.g. - above and + below).

Mobile systems are very effective and can find small holes very effectively but sensitivity of the system is affected by site conditions and configuration of the installed geomembrane.

One limitation of Mobile / Walk Over geomembrane integrity surveys is that the depth of cover over the liner should not exceed one metre.

Fixed systems

Fixed or permanent systems require a gridded network of sensors installed below the geomembrane the density of sensors depends upon the resolution required in the data, normally the grid size is designed between 3m x 3m to 10m x 10m. The accuracy of the fixed system with manual analysis of the data is approximately 10% of the grid spacing.

Fixed / permanent systems can effectively detect very small holes and can perform equally as well as the mobile system. The depth of cover is unlimited and testing is much quicker than by mobile, meaning that so long as the installed sensors and cables are durable enough the system can be tested regularly whenever the client desires.

Another advantage of fixed systems over other options is that by virtue of the permanent nature of the site installation integrity alarms, monitoring systems and automated damage positioning systems are all possible add-ons.

Commercial and Industrial Application of Leak Detection

The following are a list of applications where Sensor has successfully deployed it leak detection and location services:

• Dirty Water
  • Anaerobic Digesters
  • Evaporation Ponds
  • Waste Thickeners
  • Storm Tanks
• Clean Water
  • Service Reservoirs / Potable Water Storage Tanks
  • Lakes / Impounding Reservoirs
  • Chemical Free Water Treatment Lagoons
• Waste & Industrial
  • Hazardous product storage (chemicals, fertilisers etc)
  • Hazardous waste storage (liquids and solids)
  • Temporary waste storage for incineration and micro electricity production
  • Landfill lining
  • Landfill capping
  • Leachate lagoons
  • Landfill remediation
• Anaerobic digesters Construction & Civil Engineering
  • Green roofs
  • Brown roofs
  • Data centre roofs
  • Security roofs
  • Storm ponds
  • Tunnels
  • Bridges
  • Underground parking facilities
  • Basements
  • Substructure protection
  • Nuclear waste storage facilities
  • MOD underground structures
• Mining
  • Process ponds
  • Storm ponds
  • Leach pads
  • Tailing ponds
  • Canal / channel linings