The "foot" is composed of (now) solid material, and sitting on a concrete pad onto which the reactor building was constructed. Around the building is the "New Safe Confinement" structure.
Does the New Safe Confinement also extend into the ground?
It doesn't, but after the disaster, the basement areas were eventually filled with a lot more concrete. It's not just the very thick concrete pad between it and the groundwater, and it no longer generates enough heat to threaten to melt through.