jmw: most likely, in the geothermal system you saw, there was no actual pumping of ground water. More likely is that a u-shaped tube was inserted vertically into each well to act as a heat exchanger, both ends of the u-tube would then be piped back to the building cooling water system, which would then be a closed system. That water likely drove heat pumps to provide both heating and cooling.
Such systems can be very efficient. But they also have very high installation costs. There's always a tradeoff.