The Northridge Lumber Mill Crate is located in Northridge Lumber Camp of Western Plaguelands. [48.4, 31.9]
The sturdy crate sits in the middle of the lumber mill surrounded by debris and very zealous followers of the Scarlet Crusade.
Objective of
You can place the 
[Barrel of Plagueland Termites] on top of the crate for the quests: