Yes, the oil came from the ground, unfortunately there are about 20% additives per quart of oil, plus the metals from the wearing of parts in the engine. There are lots of pathogens that eat oil as well as plants. Ford had to do that at the River Rouge plant from when it was in operation. Found that out on a tour.
However, I used to dump oil back behind the garage. When I put an addition on many years later and had to dig up the ground for the foundation, the oil was in tar clumps just as I had poured it. None of it "leaked" into the ground!!