If this turns out to be something worth doing, I'll drill some test holes and see exactly where the water table is located and the condition of the soil above it.
I might install a remote temperature sensor down in the water table.
If it gets stays around 48deg all winter, then I can think about buying
the loop pipe.. It's a plastic that conducts heat real well.
I think you are (above) talking about an open loop system.
That type of system requires that some
professional wells be drilled.
I'm more interested in a closed loop system. Here's one used in a pond.
Some pics on this page, half way down:
Geothermal heat pumps at home
The pipe is filled with glycol and water. It's a sealed system.
The water is pumped out of the house to the loop, where it's
warmed up to 48f and comes back in to the heat pump exchanger
where the heat is sucked out and pumped into the house.
Some of the newer systems actually use copper loops and run
the refrigerant (freon like stuff) underground and skip using the water-glycol mix.
They say it's a lot more efficient..