Advice for purchase of property with underground oil tank

[EDWARD M.]

I put an offer on a two-family home with a decommissioned underground oil tank. I just found out that the oil-tank is actually under the ground floor apartment and the current owner will not allow for soil testing because it would require drilling into the floor in the apartment. He is providing DPW documentation showing the tank was decommissioned and inspected by the town in the early 90s. I have read that this is still a hazard and soil-testing should be done because the owner does not have documentation showing the tank was properly decommissioned and no leaks were detected (soil tested and cleared of spillage). I don't know what to do!