When I was doing fieldwork, the most stressful time was during the first five feet of drilling. Why? Utilities.
Sure, you have a state-specific marking program run by the utilities (who don’t want you breaking through their stuff) that will send someone out. But they may be off in their markings, late in getting to the site (as in a day or two after the site goes “live”), or you may be drilling on private property, in which case utility locations are often just an educated guess.
I have hit two utilities. The first was a probable water line about 2 feet from the marking. The casing bounced off it, we realized something was wrong, and we stopped quickly without breaking through. In that case, we went through super-clean sand and then went “thunk” and the driller realized we were drilling through bedding material. We didn’t break the pipe because we were just pushing the casing with no real weight on it.
The second utility I hit was in an old industrial area. The area I was trying to drill in had every utility you could think of and there were only two narrow spaces available. So we tried to thread the needle. It turned out that those two spaces were occupied by old (unused) steam lines, which we broke through. We had apparently no soil for the first couple feet. In that case we gave up and told the project manager he was just going to have to live without monitoring wells over there.
I have been extremely lucky. Better geologists than I have hit things spectacularly. You go through all sorts of hoops, do a walk through with a property owner (“now I am going to be drilling in this exact spot, ok?”), and then you hit some sort of irrigation/drinking water/waste removal line that they didn’t think of and have a very public (and possibly very stinky) mess. And that’s not taking into account the ones that are dangerous to hit.
So, even if I’m out in the middle of nowhere, I still hold my breath until we’re past the first couple of feet.