It could have been, but most likely at that depth the well water was located under a layer of clay (confining layer. virtually nothing gets through clay. What can happen though is that shallow ground water can get contaminated and as it moves through lenses in the sub-strata, flow into a deep aquifer and then that gets contaminated.
The rule of thumb for drinking water is if comes from a well then it does not require any pre-treatment because of the natural filtration. But for your own peace of mind if you ever buy another place with a water well, have it tested prior to closing the purchase.
Some communities on the east side of Houston have red worms in their water and I read about something really bad that would infect you if it went up your nose. Don’t remember any details.