I've looked into this exact idea myself. It lead me into a summer long learning endeavour geared towards DIY geothermal and while the concept is very sound and will work I have found one major down fall. The ground will only cool your water to about 50-55 degrees. Great to remove the sensible heat, but does nothing for latent heat. In other words, you will have a cool but very damp home. A heat pump of sorts is necessary to drop the air exchangers coil cool enough to dehumidify at any reasonable rate. I could go on for hours about this as I was very seriously considering the project this summer but due to the size of the project I've decided to hold off for a future date. If you really want to give it a whirl start searching for DIY geothermal info. Keep in mind that it takes 600 ft of underground line per ton of cooling. If you really want to dive in, check out DIY R290 refrigeration. There are a few ppl out there who have done this, but trust me its not a simple project or for the faint of heart.