This short-term airing-out may not be enough to clear out all the contaminants from the air inside the home.

., we are buying a park now in NC that has a contaminated water well.  

Usually the State has clear guidelines on this and you don't want to be held responsible in the event of soil contamination or environmental hazards to the property or the property owner could come back afterwards on this issue.

Is it enough if the seller has a policy that covers contamination?

The issue is to confirm if the soil is contaminated and the extent of the soil contamination.

Any possibility of contamination form those?

ISSUE:- Asbestos contamination.Contractors who do this work must be certified - - why, they need protective gear for the worker(s) and to shield the room so as to not allow contamination to spread throughout the house. 

Ultimately if the tank is no longer in service, it should be removed to mitigate the risk of future problems (contamination or simple an inability to sell the property).  

We spent $3600.00 to have the tank and 40 tons of contaminated soil removed.

David:I remembered another acronym for you: ESA.A Phase1 environmental assessment is predominately a paper exercise that identifies any real or potential environmental contamination.