Are Audio Volumes removed from the game?

This page says they exist: https://docs.unrealengine.com/latest/INT/Engine/Actors/Volumes/index.html#volumetypes

But I’m running 4.5 and don’t see them in the editor. Is this a bug, or have they been replaced with another method of creating volumes that you can associate with sound?

They may have been renamed somehow but these are actually reverb volume - you may use them without any associated reverb effect, just tweaking the “Ambient Zone” settings for interior/exterior volume tuning.