It doesn't have to be obviously near it for contamination to occur, depending upon how fast the water flows and what's beneath us. Aside from those tunnels, I mean.

[He tilts his head curiously, although he knows she can't see him.]

I'm not entirely certain I follow what you're saying. Can the dead here become demon possessed? Do they rise and attack the living? If so I'd say it's best to get on this burning detail sooner rather than later.