I agree with Phil about getting actual code info, but I'm thinking that it's your county's Environmental Health office that you want to talk to:
140 Stonewall Avenue West
Fayetteville, GA 30214-1520
If you are looking far a quick answer: In general, wells need to be 100+ ft from septic systems. But depending on what's in the retention pond that could be different. If it's storm water run off, no biggie. If it is something that is environmentally nasty, then 100 ft may not do the trick.
Dixon Gary Realty