My shallow well is into an aquifer that is made of blue clay, that holds a huge amount of water but gives it up very slow
I have drilled a lot of wells in Michigan and I have never known Blue Clay to give up a drop of water. Only if there is a small sand vein running through it in your bore hole would you be able to get water from it.
Your right about all shallow wells not being polluted. Most of the wells I drilled there were under 50 feet and many were only 25' deep.