A: Some vector mapping testing agencies claim that they can reliably test through overburden. Results from testing through heavy overburden are invalid, inconclusive and unreliable due to limitations such as:
- – #1 There must be a continuous layer of water on the membrane within the left in place perimeter wire. Water must always reach from any breach to the conductor cable. Gaps in water coverage can result in missed breaches. There is also no way to confirm that the left in place perimeter wire is in good condition, and left exactly as is after the initial vector mapping test.
- – #2 Vector mapping can not test transitions, details, around grounded objects, and can not reliably test verticals. Breaches could have been missed during the initial vector mapping test.
- – #3 Drain mat, root barrier and insulation are electrical insulators, disrupting the electrical signal from the top of the overburden. A continuous, unbroken water path must be present from the top of the overburden, through electrically insulating materials to the saturated membrane. There is a high probability of false negatives due to all the potential breaks in the electrical circuit.
- – #4 Any grounded items above the membrane will produce false positives.
Valid, reliable and repeatable testing can only be performed on exposed membranes.