In landfill design, the witness zone is used to ascertain whether which liner is leaking?

• A. Bottom liner
• B. Upper or primary membrane liner
• C. Filter medium
• D. Compacted clay liner

Answer: (D)

In a landfill with a layered liner system, the witness zone acts as a sentinel for the integrity of the bottom barrier. It’s a monitored layer placed in the barrier arrangement specifically to reveal leaks from the compacted clay liner. If the bottom liner starts to fail, leachate can migrate into this zone, where it can be detected, sampled, and indicate that the compacted clay liner is leaking. This setup provides an early, directly observable indication of bottom-barrier leakage before contaminants could escape to the surroundings.

The other components play essential roles in containment, but the witness zone’s purpose is to witness leakage from the lower barrier, hence its association with the compacted clay liner.