juliendogg
the water-table and underground rivers (where you'd drill a bore hole for a well) are different things. True if you are in the mountains then I'm not sure where the water-table would be. It also depends a lot on your location and how wet or dry it is. I'm fortunately (or unfortunately depending on how you look at it), UK based and it is a very wet place we have widespread flooding atm in some parts of the country.
It needs to be appreciated that soil, dry soil especially is a very good insulator, (they used to make walls of houses out of it), so won't be very good at heat transfer. If it's damp or wet it will be much better. It may work but reread my last post with regard to the fact I have a 100 litre tank 8 feet down (bottom foot or so in the ground water and it still warms up in use (all be it slowly).
Diggrr
That could work but make sure any connections that will be buried are very secure. I'd back fill with a smooth gravel up to the water-table depth as it would allow more water to tube contact, but this will cost a little to buy. another thing to take into account is the possibility of the pipe being squashed as you back fill.
The tank I used is not the most efficient way to do it as the surface area to coolant ratio is poor. It was just the simplest solution that presented it's self to me at the time.
UnLoadeD
The PSU build is detailed on zerofanzone and there is a image link on the main page.
The later updates are not included yet, which are a bracket from the block to help cool a coil that was getting too hot for my liking some general thinning out of the plug wiring and cut-outs in the PSU case to help the natural heat rise airflow.
One last thing to consider is any coolant or water that you run through your systems tubes or blocks that's colder than the case ambient could cause condensation to start to form, related to the relative humidity