Decomissioned oil tank

[Dominik Gajor]

I'm looking to flip the property in NJ which is being sold by the bank in the as is condition. I believe this house at some point had an oil tank which was replaced by the gas furnice.  What I want to know is how do I find out if the oil tank was removed/decommissioned properly? To my understanding tank can be pulled out or filled with sand. In the event when it is filled with the sand, soil should have been tested and report/certificate generated. Where can I find/pull this information from? I don't want to get stuck with the problem of digging out the tank and soil decontamination which could get pricy really quickly and turn the deal into a dissaster.