Suggestions are useless unless you know what processes were carried out on site. Where are the Heintzmann archives?
Product makers are cost-concious. Expensive materials are not scattered to the four winds.
I believe Amos is correct. You do not say that you have contacted the City people who ok construction licenses and carry out assessments.
Have you contacted an environmental assessor?
What is on site now? Houses, stores or mixed? If already residential or mixed, why not a condo on the site?