The new owner is relieved of any liability for the contamination as long as they did not cause it. 2.

The sellers mentioned they knew nothing about it.For stores rented to dry cleaners, are there any contamination issues which greatly diminishes the value and imposes liabilities for current and past owners?

If at any point the property owner pays off the overdue property taxes before the lien expires (period may vary by state), the county is the party that earns the interest.Properties that are owner-occupied (as indicated by a homestead exemption showing up on the annual tax bills) or have a mortgage are most likely to be bid on because they have a higher likelihood of being paid off either by the homeowner or the mortgagee (the lender); the homeowner probably doesn't want to lose his/her place of residence and the lender probably doesn't want to lose its investment.If no one has bid on a lien, there are likely issue(s) with the property that, in the eyes of bidders with investor mindsets, render the property valueless, for example:the property has no direct access (landlocked or waterlocked),the property is too small to be built on as-of-right per the municipality's zoning codes,the property is contaminated (a Phase I environmental report would scour records on the property to see if contamination is likely, and if so, a Phase II environmental report would be done and soil, etc. samples would be taken to confirm the contamination),the market fundamentals indicate little probability for profit given the level of risk, such as high vacancy rates, low rents, or slow sale/rental velocity,the property is in a "poor" location due to many of the types of things that turn off people looking for a home in which to live, such as high crime; poor or nonexistent infrastructure, such a streets, water & sewer, etc.; too rural/too urban; neighboring uses detrimental to the property's value, e.g. railroad, warehousing/industrial district, jail/prison, cemetery, etc.I hope that helps!

Is it even legal to sell a contaminated home at an auction without any disclosure?? 

I have fixed the devasting effects of salt chloride contamination in concrete to the tune of hundreds of thousands of dollars. 

If you are considering switching to a different heating system you will need to remove the tank and clean any contaminated soil.

Soil testing with the tank still in place will not produce 100% accurate results that there is no contamination.

Infected or (black) water combined with time and high temps brings about a contamination issue. 

What is the likely hood of it being contaminated if it has already been decommissioned?

In addition, any real estate attorney worth his price will advise the buyers not to purchase the property until the tank is removed and state certification has been received proving that there is no underground contamination.