Our state regulations require a "seal" to protect from contaminants.

We also found out that if they had detected fuel they would require more soil to be removed and it is now considered contaminated soil and has to be disposed of in a special area.

During the inspection, they found an underground oil tank with contaminated soil on the premises.

That being said, any time you are interested in a property built prior to 1980 you need to be very mindful of asbestos and lead contamination.

[No coverage for] Water below the surface of the ground including that which exerts pressure on or flows, seeps orleaks through sidewalks, driveways, foundations, walls, basement or other floors, or though doors,windows, or any other opening in such sidewalks, driveways, foundations, walls or floors;...Wear and tear; marring; deterioration; inherent vice; latent defect; mechanical breakdown; rust; mold;wet or dry rot; contamination; smog; smoke from agricultural smudging or industrial operations; settling,cracking, shrinking, bulging, or expansion of pavements, patios, foundations, walls, floors, roofs orceilings; birds, vermin, rodents, insects or domestic animals.

I would certainly make sure you did environmental due diligence including having the sellers sign an environmental questionnaire indicating whether they know of any environmental concerns.I have seen environmental contamination from gas stations go under major interstates and impact properties several hundred feet away.

and many times you will find your waste line is contaminated and needs to be snake ( easiest if able) or is beyond useful life and needs to be replaced

The couple sued (and lost), thinking the words in the paperwork had meant a non-contaminated well.

@Brandon Ellis That's going to depend on the extent of the contamination.  

Contamination issues are the legal responsibility of the current property owner regardless of who caused them.