concentration of the element in the solution. and what was the element found in the solution? lead. this meant that it was leaded gasoline on the camiolos' wood floors. but how did this happen? since leaded gasoline hadn't been sold in this country for over 15 years. >> many of the poorly constructed houses that i've looked at were built in the early '70s, and they were built by contractors who were cutting corners. >> flooring contractors often used gasoline as a thinner so the varnish would go onto the wooden floors more easily. this was cheaper than using high-quality thinners. >> no one refuted the fact that that was a common practice, that they did use gas in finishing of the hardwood floors. so, i am convinced that's where that gas came from. >> so that was really the moment where we said, here's the final piece of the puzzle. if this is leaded gasoline, it all makes sense, and it makes sense how it would be there and why.