I don't know if that is so huge a problem with underground detonations, unless there's some underground water stream flowing straight through the test site. But you would think they would have checked for such things.

I just today heard in the news that only about 20% of the land area of NK is suitable for any kind of agriculture. So, that would leave lots of barren space far away from rice fields for nuclear tests.

The political ramifications must be much worse than the ecological right now.