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.

I'd say your biggest concern will be environmental issues, lead paint, asbestos, or other contaminations that you'll likely have in older homes and in that price range, probably updates were limited if any were made

Also be aware that some old farm houses have underground gas tanks that have deteriorated and contaminated the ground, this is a big concern that many people overlook.