1. Service Description
The Electrical Leak Location method is a very sensitive technique that accurately locates leaks (if they exist) in geomembrane liners in landfills or impoundments. This field-proven method has located many leaks not previously found using conventional methods.
Layfield supplies Leak Location surveys across Canada and parts of the USA. Leak location surveys are effective for both exposed and backfilled geo-membranes. The Electrical Leak Location method works on all polymeric geomembranes used singley or in combination with GCL’s or compacted clay liners. The method is not effective on GCL’s or compacted clay liners that do not include a geomembrane.
Once you detect leakage in a sump or a monitoring well localizing and repairing the leak can be a difficult proposition. The Electrical Leak Location method is the fastest and most accurate technique available to pin-point leakage.
Since Layfield installs all lining material types, we can fix the leaks we find. The Electrical Leak Location method and Layfield combine to provide the most effective repairs for any lining material.
Although geomembrane liners are a low maintenance option, they still should have a defined maintenance program. Layfield can design a periodic maintenance program for your lining system that can include regular leak surveys. A maintenance program that uses the powerful tool of a Electrical leak location survey can clearly demonstrate your environmental compliance.
Layfield service group can assist you in developing a repair, maintenance, or installation plan, using the Electrical Leak Location method.
2. What’s is Electrical Leak Location?
The Electrical Leak Location method detects electrical paths through the liner caused by water or moisture migration through a discontinuity in the liner. Electrodes placed in the soil or water above and below the geomembrane liner are connected to a DC power supply. Because the geomembrane liner is an electrical insulator the impressed voltage from the DC power supply produces a uniform electrical potential distribution in the material above a liner when no leaks are present. If a discontinuity (either a leak, or an electrical ground) is present in the liner electrical current will flow through the discontinuity. Leaks are located by searching for areas of non-uniformity in the electrical potential in the water (or backfill) covering the liner.
The Electrical Leak Location method will detect areas of electrical non-uniformity in both water or soil coverings. Depending on the application the Electrical Leak Location technique can detect leaks as small as 0.0065 square centimetres (0.001 square inch) and less. This lower boundary represents a "pinhole" measuring 0.9 millimetres or 3.5 hundredths of an inch in diameter. The Electrical Leak Location method can be used on liquid impoundments with exposed liners at any time and as a pre-service inspection on backfilled liners (normally prior to backfilling the anchor trench).
3. Surveys with Water Cover
A leak location water survey is the most accurate method for finding leaks in geomembranes. Primary and secondary liners of water-filled impoundments are scanned for leaks using leak location probes and associated instrumentation. The operator uses the probe while wading in water that covers the liner to be inspected. Please note that water is required as a conductive medium and must cover the area that requires inspection. Every square foot of the submerged liner is surveyed. Leaks are located accurately to within 12.5 millimetres (0.5 inch) and immediately marked with sinkers and floats. The locations of the leaks are also measured relative to a survey grid for a permanent record. To survey the bottom, a minimum of 150 millimetres (6 inches) and a maximum of 760 millimetres (30 inches) of water must cover the liner. To survey the side slopes of a pond the water level is raised to the operating level. Side slopes are then systematically surveyed with a long-handled probe, about 5.5 metres (18 feet) long. The locations of the leaks are referenced to fixed points on the berm of the impoundment or landfill. When more than 5.5 metres (18 feet)of the side slopes are immersed, the manual survey of the side slope must be conducted in stages. The water level is raised or lowered in stages to allow approximately 5.5 metres (18 feet) of the immersed side slope to be surveyed at a given time.
Another survey method for side slopes is the water lance method. In this method a stream of water is directed onto the liner. The stream of water is connected to the voltage source and the instrumentation will indicate if a discontinuity is found.
4. Surveys with Soil Cover
A leak location soil survey of a soil-covered geomembrane liner is a highly effective method to find leaks including leaks caused when placing the protective soil cover on the liner. A grid is laid over the lined area and measurements are made using a portable dual-probe device. The protective soil cover must have enough moisture to be conductive and allow an electric current to flow through the suspected leaks in the liner. The leak survey for covered liners is limited to installations where the soil cover is not frozen. Typically, leaks with a diameter greater than 3.0 millimetres (0.12 inches) can be located in a geomembrane covered with up to 600 millimetres (24 inches) of soil. The leak location sensitivity increases as the thickness of the soil cover decreases. Therefore, testing for leaks with only a portion of the soil cover in place is recommended if the thickness of the soil cover will ultimately be greater than approximately 300 millimetres (12 inches). Electrical Leak Location surveys of backfilled liners need to be electrically isolated from the ground. This is easily accomplished by performing the survey prior to completing the backfill of the anchor trench. For best leak detection in an existing installation, the anchor trench may need to be excavated in order to expose a strip of insulating lining material all the way around the impoundment. If a backfilled liner can be filled with water then a regular water survey can be performed. A water survey on a backfilled liner is less accurate than a water survey of a non-backfilled liner but is quicker than a soil survey.
5. Installation Considerations
The Electrical Leak Location method has a number of requirements in order to ensure accurate and conclusive results. The most important precaution is to eliminate or limit electrical grounding points between the inside and the outside of the liner installation. Any electrical path from the water or soil being surveyed, to the subgrade outside the liner will create a signal that looks like a leak. These ground faults can also be caused by concrete or steel structures within the pond. Steel pipe penetrations, batten bar on structures, and soil cover materials that connect to the subgrade. A less obvious, but very common ground fault is a steel valve body that can be located in a plastic pipe that penetrates the liner. Layfield can assist the designer by supplying details that will eliminate ground faults when designing the lining system.
In designing lining systems for hazardous materials it may be desirable to have periodic surveys of the liner. Designing for periodic Electrical Leak Surveys may require additional changes that will speed future surveys. Your Layfield representative can assist you in adapting your design to allow for periodic monitoring and inspection.