Welcome to ER, Charles
Already having a radiator in the air duct is a good start. Yes, plumbing it to a source of cold water will cool the house, plus it will reduce humidity (good in Alabama). But I can see a few problems you'll need to solve:
- Since the radiator/duct was installed for heating you will have to find a way to remove condensed moisture,
- Making a ground loop takes some work,
- The ground loop will have to be large to soak up the heat. Heat diffuses slowly in the soil, so you will need a large surface area, while it can build up quickly, as Daox found out when trying to dump his house's heat into the basement sump water.