Where is the water coming from and how do I stop it?

Its coming from the ground. Concrete is porous. Workarounds would divert the water to someplace else.

What's under the 10" is the question - a good amount of gravel, possibly insulation, and definitely a vapor barrier are done these days, but weren't 40 years ago.
Concrete gets more porous for about 40 years as well.

Your question is incomplete. Humidity or ground water?