Using the pond may be possible. 90 feet of sand may not be the best condition for a ground loop. I would suggest consulting with an accredited professional in your area before ruling anything in or out.

SR

Here is a link that might be useful: IGSHPA, International Ground Source Heat Pump Association at Oklahoma State University

Sounds like you have an ideal set up for geothermal. Try asking for information on the www.geoexchange.org forums, quite a few professionals are on there and will give you solid advice. I know that a few do pond loops all the time because they talk about them. And, some live in florida and the south so could give you tips as well.

As for me, I live in a coastal area in the northeast and my vertical ground loops go through a mix of sand and gravel, but it sure looks like sand to me when it gets drilled. My loops work very well. I LOVE my geothermal system. It was just put in in late December and has kept our house so warm and cosy.

Question for "sunnyflies." Did you have to case your wells (expensive, right)? How deep were they?

We've been living with our geothermal system for 2 years now and the the thing runs fine. We live in the northeast and use it for heating more than cooling, but it does both jobs very well. Best part is waving at the oil trucks as they drive by the house!