There is a good chance that you are smelling hydrogen sulfide which has as a source bacteria. Chlorine is a good way to treat for bacteria, but you need to be sure of your dosing. Too little and you will have no effect. Too much and you will have a very high chlorine residual, which could lead to undrinkable water or even worse the formation of THMs (which are carcinogens), though that is more likely to happen in surface water rather than ground water.
I would want to know what kind of bacteria it was if possible anyway, and try to identify the source so that you don't have this problem again and are sure that it isn't being contaminated from any real unsavory sources, if you get my drift heheh.