>>5824639 (pb)

>George Washington Parkway in Virginia is shut down between the Capital Beltway and Virginia Route 123

So you're telling me there's a sinkhole right outside of the CIA in Langley? The sort of thing that might happen if you were to try to dig a level tunnel from there to the Potomac? Hmmmmmm?

>>5826178

Topography in the area is pretty up and down. The Potomac sits at ~15m above sea level there while the surrounding hills on that southern bank are anywhere between 15 and 25m above that. I'm sure erosion could've done the job entirely, but I don't think a tunnel collapse would be impossible.