Mystery Igloo

This mysterious igloo-like structure is on U.S. 25 in Madison County, just a few minutes South of Whitehall.

It's fenced in with a barbed wire security fence and a locked gate, with several small trailers and outbuildings on the property, and lots of government vehicles. The mailbox is blank and there are no signs or anything else providing even the remotest clue as to what goes on here.

The first idea that comes to mind, of course, is that the igloo might be some sort of silo or grain storage bin.... but the property isn't on a farm, and no agricultural equipment or farming trucks have been seen coming or going from the compound.

What the heck is this place?