Have had oil from an old pipe line that I did not get removed, There was enough oil that most of the pond (about 7 acres)had a film on it. with the hot days of a Texas summer coming on the oil disappeared, it did not take long THANK GOD----but the source of the oil was easy to identify in my case. In your case the oil could also go away,----but where is the oil coming from and how much is there? keep us posted