It turned out to be true that water vapor (steam) was splashing (erupting) from underground in June.
10/13/2011, Tepco conducted measurements by robot around where water vapor was splashing.
They measured 4.7 Sv/h, where it was 4.0 Sv/h in June.
It is located at South east side of the reactor 1.
According to Tepco, it was splashing from underground in June, but now it’s stopped.
They assume it is the highly contaminated water that fills the basement floor.
It is assumed that melted fuel rods are sinking deep underground, which is called China Syndrome.
(Source)