An old unused well can cause the problem if it is in the cone of depression of the new well. Meaning that the new well is drawing old stagnant maybe smelly bacteria laden water out of the old well. So we'd have to know why there was a need for a new well.
Here, treating the well first usually wastes time while solving nothing and can cause problems, although the odor will go away temporarily because the chlorine oxidizes the H2S or kills the bacteria producing the H2S. Then the odor returns in a few days or a week or two, and you start over.
The anode rod removal or replacement with a different material, is only going to help IF the cause of the odor is bacteria colonizing the water heater. So if the odor is in the cold water too, and not only in the hot water, doing anything with the rod is not going to help. IF the odor is in the hot water only, raising the temp of the heater to 140f stops the odor.
If the odor is in the cold water, it can be caused by IRB, SRB and/or MRB (iron, sulfate and manganese reducing bacteria). They are harmless to humans and animals. They live in the ground and surface waters; and love water heaters where the warm water is beneficial to them. If the odor is not caused by bacteria, then it it is naturally occurring H2S that comes into the well with the recovery water. Then you need equipment to treat it. There are a number of types of equipment and some are much better than others. Some of them are also used to kill the reducing types of bacteria; like chlorine, ozone, hydrogen peroxide in a number of different types of application. Such as solution feeders, inline pellet chlorine or pellet droppers. All are followed by a filter to remove the chlorine etc.. I usually use an inline pellet chlorinator and a Centaur carbon filter. You can also use an air pump system, using the same filter. Or a greensand filter only, or a Centaur carbon filter only although I have not done that.
Gary
Quality Water Associates