In your contract it should be marked off what kind of sewer system you have on there.Also, if you're removing the tank, it's important it is properly removed and an environmental test is done to make sure there are no contaminants. 

If it happens the soil is contaminated, the State of Oklahoma fund will pay for the cleanup for soil clearance.

Usually it's because there is lake water or drinking water or groundwater degraded that can be contaminated by septic or your project. 

People end up abandoning lots all the time because of title issues, sinkholes, ground contamination, setback and other zoning problems, and a whole host of additional problems. 

The ground below is likely contaminated.

There was an old superfund in the 80s to clean up metal contaminants in the soil from the old mining activity, so maybe check into that if.

I also have a large former refinery property that is in a sub S that I cannot ever put in my name due to contamination issues. 

So even elements that don’t appear damaged can be contaminated.

I was unable to cook anything for my family for fear of cross contamination without hot water.

If a parcel was owned by a company that manufactured anything, especially metal things or used chemicals, you can bet there is some level of contamination.