So instead of getting a pond built for geothermal, I am going with vertical boreholes instead. I have a well driller coming tomorrow and I've been quoted 12 dollars per ft. The pond will have to wait.
The vertical boreholes will be better for geothermal in your area. The bottom of a reasonably deep unaerated pond, say 12 feet, would be at 39 degrees in the winter, and probably low 60s in late summer. The deep soil temperature is about 53 degrees year round.
