The article isn’t very clear as to what underlies St. Meinrad.
Where I live, the below-ground temperatures are somewhere around 56 degrees; the average annual temperature here. And it’s that way far, far underground, so that water from deep wells even two thousand feet deep is very little different in temperature from cave temperatures near the surface.
So, around here, you would be pumping up not-too-comfortable air of about 56 degrees. But it’s true that it would take a lot less energy to heat 56 degree air to, say, 70 degrees than it would take to heat 20 degree outside air to the same temperature.
But heat pumps utilizing ground heat have been around for a long time. Nothing really novel about them. Some people use springs for the same purpose because heat exchanges faster from water than from earth or stone. Since cold air from the surface pumped down into the hole tends to cool the earth surrounding the pipe, it’s not as effective as one might wish unless the piping goes through layers of moving water.
Now, if one was at Hot Springs, Arkansas, it would be different because there are thermal springs there that arise from far deeper in the earth’s crust than anyone would ever dig. What they have there are very deep faults in the earth’s crust. Water from the surface seeps down into those super-deep faults and is pushed back up by a combination of water’s self-leveling and the greater volume of the heated water.
Personally, in the absence of flowing water, volcanic upthrusts or extremely deep faults through which water can percolate down and back up again, I don’t think this is any kind of miracle energy source.