I once was required to remove the top 6 inches of dirt from a 50 x 100 foot lot (asbestos contamination complaint from the clean air division of the Dept of Ecology).

Moisture and other contaminants that can get into a refrigerant system, if its not evacuated properly can severely shorten the life of a compressor.Typical condenser costs 1,000 or so and proper install can be 6 to 8 hours depending on the system conditions.  

A lot of that will depend on your state's particular laws - both on how a non-leaking tank is to be decommissioned and how a leaking tank is handled.If there is a leak, now is the time to find out, and possibly back out of the deal, even if you sacrifice your EMD.Here in MA, someone who buys a contaminated property acquires the responsibility for cleanup. 

Black mold is like any other household growth/contamination...it doesn't come back unless the conditions that caused it come back...did the remediation company give you a certificate or warranty?

Opening a kitchen window painted with LBP, for instance, while preparing food could cause lead contamination.

Area and neighborhood are great but always rumors the area wells have had contamination in past years.

Contaminated soil, lead based paint is still used commercially, just not residentially, high levels of radiation, mold, asbestos. 

Unfortunately, no banks will loan money on the property because the land is contaminated.

Age generally isn't a disqualifier.Some obvious things like hazardous conditions (contamination / structurally unsound) would be an issue. 

I think there are other options that eliminate the "cross contamination" from being sued in one LLC and allowing the plaimtiff to get to your other LLc's, you personally or EVEN your assets or equity in the defendant LLC!!.