A properly installed and grouted well will not have chemical run off.
Minerals....iron in the water does stain...but, is harmless.
In an ideal world, yes. And I always thought that too until I moved up here. Well, it's not run off, but we have come across several wells where the acquifer in the bedrock has been contaminated
Yikes. Then you need to hope that your driller knows that the acquifer is contaminated and seals it off, and that your neighbours wells have the same construction so that nobody is cross-contaminating. But, I've never seen that anywhere else, so it requires a certain rock formation and environmental conditions. Where we were involved, MDH came across a rock formation that no one knew what type of rock it was. They came up with some kind of name that was more descriptive of it's characteristics, rather than a proper name like "grey granite" or whatever. In that situation, the "contamination" was not from industry but was actually in the rock formation itself. We are in the meteorite strike area of Northern Ontario, so sometimes there are some pretty funky things we see.
There are/were houses not all that far from here that no one can sell because they are out of reach for city water, but you absolutely can't get drinkable ground water. Awful, just awful. I think in that case, a company was held responsible for the contamination, but not sure what ever came of it.
I have heard of a similar situation in southern Ontario somewhere. That area was linked to industrial development as well of some kind if I remember correctly.
But, just to set everyone's mind at ease, this is rare. In over 20 years of drilling wells, we have only come across this for the first time first hand up here in the last 5 years or so and it was for us only one particular location. So, if you're not near industry that is pumping nasties into the groundwater, not near mining activity and haven't been struck by a meteorite, you should be ok!