@John Lopez, thanks for an insightful response. I agree with you that if there is clean up and it leads to an area beneath the structure of the property, tthan the clean up could be much more than the amount of equity in the deal. I proposed to Fannie to dig up the area with the anomaly, if there is a tank to remove it at my own dime and still purchase the property as long as the area is not contaminated. Which I thought was a no brainer. The seller's agent responds with "you cannot touch the soil".
To answer some of your questions:
1. Property was built in 1955. How do I get access to a sanborn map?
2. I will ask the environmental company to see if this is possible? Again, the seller does not want me to touch the soil which is ridiculous
3. Where can I get access to old site plans?
4. This is a solid idea, I will talk to the bank tomorrow morning.
5.I will check with NJDEP tomorrow. I was told that the town should have permits if the oil tank was removed but as @Kelly Arthur stated its really NJDEP that I need to call. Thanks for the insights. Please share any further insights you may have that will help me through this process.