if you do not have a runoff system where the water is released into the nearest body of water, then this is very ineffective. He claimed a 40% efficiency rate with the release of the water. That is not enough for deep-freezing temperatures.

I think they must have been talking about a different type of system?

If I am not mistaken, the type of aquifer geothermal being discussed pulls water out of one well, pulls heat from it (or dumps heat into it, depending on the season), and puts all the water back into another nearby well in the same aquifer. No runoff. These open loop systems can be municipal scale, or just your own house if you have a big yard.

The only systems like this that I know of that are not water balanced are ones that are tied to a water supply. So, for example, much of downtown Toronto uses a central air conditioning system that pulls "coolth" from the water from near the bottom of Lake Ontario. After the heat exchangers, the water is then passed on to the municipal drinking water system rather than being pumped back to the lake. (I guess it eventually gets back there as wastewater)

The open loop aquifer approach only works where you have lots of good groundwater in somewhat porous soil. Cities on coasts are better off using the lake or sea as the thermal reservoir, but generally lose out on the efficiency of storing heat in summer and pulling it back out in winter, since large bodies of water are not measurably warmed by the amount of heat dumped into them during the summer.

Jim