I found this to be interesting.
A quote from that page you linked: "Interestingly enough, there are NO signs of life anywhere in the whole complex; not even a rat or a spider. This may mean that it's just pretty well sealed, or it may mean something worse, that something is preventing things from living down there."
In my research of these sites over the past couple weeks, I've found that this seems to be a reoccurring theme in all the various reports from different explorers in all the sites. Leads me to believe that there are very toxic substances to be found below deck, on account of the fact that some of these sites (the one in Deer Trail in particular) are not sealed any longer. Rats can live almost anywhere, in some of the nastiest filth know to man. But if they can't live in these abandoned bases, there's got to be something really foul down there.
But hey, look on the bright side. At least it's not an abandoned chemical/biological warfare agent factory like they have in Russia where there's bubonic plague and anthrax just lying around on the floor...at ground level...