The witness zone is the section of a landfill located between which components?

• A. Low permeability soil and native soil foundation
• B. Lower and upper flexible membrane liners
• C. Upper flexible membrane liner and the filter medium
• D. Waste and the upper compacted clay liner

Answer: (B)

The concept being tested is where a witness zone sits in a landfill liner system. The witness zone is the space between the two flexible membrane liners—the lower primary liner and the upper secondary liner. This arrangement allows any leak from the lower liner to be detected in the space between the liners, before leachate can move on to surrounding materials. The other layers described in the other options aren’t the dedicated monitoring space for liner breaches, so they don’t define the witness zone.