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!!.

The property has been a truck terminal for years and he knows it’s “contaminated”.

If it has contaminants below the surface such as Flint MIis it worth less?

The city is passing out water filters, free water and other services to make sure people do not have to drink contaminated water.