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Electrical leak detection at depth

Q&A: GMA Techline | February 1, 2022 | By:

Q: I am taking the opportunity to ask a question about the electrical leak detection (ELD) test for geomembranes: 

We have the area covered with silt from the past rainy season, and it is estimated to be about 5 feet (1.5 m) deep worst-case scenario. The liners in this area were not properly inspected and signed off on by me due to the COVID-19 pandemic and resultant lockdown. The water is in the process of being pumped, and the pond will soon be empty.

My question is, will electrical leak detection be able to detect leakages at this depth at all? I have no experience with electrical leak detection yet. Removing the silt is an option, but the client doesn’t want to go this way, and it could cause more damage to adjacent liners.

Can the area be covered with a sacrificial liner over a 60-mil (1.5-mm) wedge-welded liner to the existing 60-mil (1.5-mm) liner? Will unwanted stresses occur once loaded and will later failures possibly occur?

Thank you for your time, sir. It is really appreciated.

A: Don’t pump the water out of the cell yet. Run the dipole method, per ASTM D7007 “Standard Practices for Electrical Methods for Locating Leaks in Geomembranes Covered with Water or Earthen Materials,” with some water covering the silt. It will greatly heighten the sensitivity of the survey. Electrical leak detection will be able to detect leakages at depth. I have seen this technique pick up pinhole-size leaks through both soil and water. You are going to need a very good survey crew to locate the damages post-survey and dig it up; however, it is done regularly here in the U.S.

This idea of covering the area with a sacrificial liner over 60-mil (1.5-mm) wedge-welded liner to the existing 60-mil (1.5-mm) liner sounds bad to me. At that point, it is time to rip it out and start over. Band-Aids usually do not work for the long term.

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