A year and a half into our residency there was a fire caused by one of our neighbors that resulted in a 6 month renovation due to asbestos contamination that included the apartment walls being repainted and our nice carpet being switched out for really cheap, crappy carpet. 

If the kid takes his stuff and puts it in another location he can then contaminate that house.

Are there now mold issues or other contamination due to the water intrusion?

If you order an environmental and find out there was a gas tank that was never removed under your 16 unit apartment building you will immediately be liable for any damage from contamination moving forward (an extreme case but it illustrates the point). 

Well today it was announced that the EPA has found lead contaminated ground.

But the state or someone tests the soil years later (while I own it or while I'm selling it) and they find to high of contaminants left from the gas station clean up am I liable?

If there's existing contamination, cleanups can be catastrophically expensive. 

I did not see any barrels containing who-knows-what contaminants inside the building. 

Different type of contamination. 

It’s a 3 family in a good location and the numbers work for me but during my inspection today the inspector asked if it had a clean E21 report to certify that there were no contaminates.