After having been in commercial use in Europe since 1999, the arc testing method for liner integrity surveys (LIS) has finally found a home among the other electrical leak location methods in the ASTM International standards system.
Arc testing evolved from the spark testing method, but arc testing is quite a different technology. Spark testing is used specifically for coextruded, conductive-backed geomembrane; while, the arc tester has been specially designed to use natural materials (soil, clay, rock) as the conductive medium for the electrical path. While the spark tester uses a build-up of electrical potential to discharge discrete sparks, the arc tester maintains a continuous electrical arc, as shown in Photo 1.
The convenience and effectiveness of arc testing in testing an installed geomembrane for leaks has helped it spread rapidly in the past five years, and not just in Europe where it was developed. The technology has established an impressive track record for locating even the smallest of leaks in projects in Chile, Bolivia, Mexico, Canada, Finland, Turkey, Korea, Japan, China, Peru, Australia, Argentina, and, finally, the United States.
Between 2009 and 2014, roughly five million square meters of geomembrane were surveyed by arc testing around the world. The method located thousands of leaks that may otherwise have remained undetected in containment facilities throughout the world.
Although the arc testing method is technically equivalent per ASTM to other exposed geomembrane leak location methodologies (e.g., ASTM D7002 and D7703), the arc tester provides some clear advantages.
Foremost, the method does not require the addition of water to carry the current for the electrical detection path. For the water puddle and water lance methods, a water truck must typically be provided onsite to feed the water-based leak detection equipment. This adds cost to a project. In water-scarce regions, these methods may not even be feasible.
Additionally, the conveyance of water requires a second laborer to assist with movement of the water supply hoses, while the arc tester can be operated by only one person. Multiple arc testing operators can be present in one area, since they don’t maintain water puddles that can interfere with the water puddle of an adjacent operator.
Also, the arc tester is more amenable to testing extremely sloped or vertical surfaces. It is far easier for an electrical arc to travel horizontally through a geomembrane to connect with the concrete or metallic vertical wall than a jet or puddle of water. And water-based methods require that sites contain a low spot where the water used to perform the survey is allowed to collect. If the water flows out of the survey area and touches the earth outside of the lined area, then electrical current will also flow out of the survey area, compromising the survey sensitivity.
As shown in Photo 2, the arc tester can be utilized on projects that do not have a low area for water collection. There is no risk of compromising the survey from water flowing off the liner.
Installations with many leaks pose a similar challenge for water-based methods. It is more difficult for these methods to distinguish between multiple leaks in a small area, since all of the leaks are connected to each other via the water spread over the geomembrane. Similarly, it is difficult to test very close to the edge of a geomembrane or a conductive batten strip with water methods, since the water will tend to splash onto the conductive feature, resulting in a leak signal whether or not a leak is actually present.
As shown in Photo 3, the arc tester has an easier time locating leaks near conductive features.
One capability that the arc tester provides that is not technically possible with the other electrical leak location methods is the testing of geomembrane with a geotextile installed over it. As long as the geotextile is dry, the equipment will have no problem arcing through the geotextile when there is a leak in the geomembrane. The arc tester can also instantaneously detect leaks through the tortuous paths of extrusion-welded patches, which takes more time and can be passed over with the water-based methods.
The arc testing equipment is also easier to calibrate and operate than the water-based methods, which often require sensitivity adjustments during the survey. An operator with no special skills can be trained to use the arc tester in a few minutes; once the unit is on and set to the proper sensitivity level for the thickness of the geomembrane, it simply needs to be passed over the geomembrane and the arc and alarm will be activated in the presence of a leak.
The new Standard Practice for the arc testing method is designated ASTM D7953 and is now available on the ASTM website.