It's a fascinating problem, a way to communicate the concept that this is not a treasure trove, not a historical site, but something dangerous that was meant to be sealed away for many thousands of years due to its hazardous nature. The parting thoughts seem most telling to me thought.

They wonder if this really worth it, since in the end coming into contact with the waste is a bit of a self-limiting problem, in that people exploring will become sick and die. It will ergo, become a "Place to avoid" anyway. If the cost is bound to be a few explorer's lives every few millennia in any case, and that's what will send the real message, then... well... you see?

Finally though, they just wonder how to construct something massive, durable, and yet not likely to be cannibalized for parts or scrap! They even raise the issue of what 400+ generations of unknowable humanity might do to the marker structure, without disturbing the rest of the site.