Airports and golf courses, on the other hand.. many uses for surface area besides living. I don’t know (truly) if the issue is really toxicity (in a well designed, reclamated landfill) or the simple fact that city services like sewer, water, gas, electric were never under-grounded there by design. You’d think settlement would be a cause for concern too, but I’d also think they have that solved if airports are made atop them.