The science channels have been awash with reports of an "underground ocean 3x the volume of the surface oceans."
First - it's sort of bunk. They're not talking about water, but "hydroxyls" - a "different form of water". Though, that's not what I'm here to talk about.
When I heard this, my immediate thought was, "Ken Ham will love this". One of the objections we have to the Global Flood story is "where did the water come from, and where did it go?"... and he'll just see this as being consistent with the story.
Of course, consistent doesn't mean true. There's still issues of how it came up, and how it went back into the mantle. The surface water we have may have bubbled up from this reservoir, but there's no real reverse (or initial) mechanism to transport such a bulk of water without shattering the earth's crust.
Ham is already fairly good about cherry-picking science to fit his pre-conceived story. I don't know that we need to add anymore gasoline to that fire... though, he does a pretty good job demonstrating how his theological position are a bunch of crackpots.