Impurities might burn into something else.

But most beneficial is that as a conditioner, clean all impurities (particles) of carbon your engine and of course, more life to the oil.

Impure thoughts?

You are absolutely correct, then you have to check for chlorine level and other impurities.

There are other purifiers that create chemical reactions to break down impurities (ozone generators).

Does the phase I include water quality testing for lead and other impurities? 

You have a complicated situation, and we know this tenant may have impure motives and could be litigious.  

Grinding the concrete will surely remove surface impurities and etc.

I would require a thick hepa-filter be used (6-12 month life expectancy, depending on the impurities in the air).

It's really all there and has been forever, as far as we are concerned.The Bible teaches over and over about planting seeds, raising and harvesting, pulling weeds, taking the impure and burning it and all that remains is what is pure.