[DB]

Cool (pun intended ;-) do they require ground water or does typical soil 15 feet down or so work well?

I’m working on my new house plans I write... The building site is up on a mountain with no hope of usable ground water nearby. I’ll have to do some research on this and see if it is practical, as I didn’t know this was actually done.

Use the septic tank leach field? Probably a bad idea…

[Wonder Warthog]

"Cool (pun intended ;-) do they require ground water or does typical soil 15 feet down or so work well?"

I don't think you actually need ground water, although I think if you DO have ground-water, the heat exchange efficiency is a little better. Also, as I recall, you don't need to get that deep, I think 2-3 feet is sufficient. There are two styles---straight down (i.e. drill a well and drop a loop of pipe down and fill in), or dig a serpentine trench 2-3 feet deep and of a length to hold the suggested loop size. Obviously, the one you choose will depend on your sub-soil conditions.

I'm sure you have found out that there is LOTS of info available on the subject.