I did, but accidents happen, those are usually farmers and aren’t trained engineers with all safety measures, someone could have an oil tank nearby and someone/car bump into it or similar scenarios.
In California, that legally drilled well has a sealed cap and a concrete pad at the top. It’s quite unlikely for anything to spill down it unless there is a flood higher than the cap.
So the concern is that a farmer will drill the well, pull up the drill head, then accidentally spill a tank of oil then the oil will go down the hole and... contaminate the hole?
In short, yes. The hole for the well works both ways; it's a fast track for any surface-level pollutants to get into the groundwater, contaminating it for everyone.
Local law may require barriers to prevent this, such as an elevated concrete pad at the top of the well. This how-to guide didn't mention anything like that. Permits help ensure that important steps aren't skipped.
You should be 100 times more worried about fertilizer runoff into storm drains than some random farmer drilling a well and then ruining it by pouring used motor oil into it.
