A neighbor of ours just happens to be in the household water biz and she came by to test our water for chlorine. Yes indeed, there is a ton of chlorine in our water right now.
As soon as I told her that we had a crew out looking at the well, she knew exactly where the Cl came from. Whenever they open a well for any kind of maintenance, they'll hit it with some chlorine to kill any contamination they may have introduced!
And it did a hell of a job of clearing out the iron-eating bacteria!
But the water people never told us they were going to do that.