When public water supplies are threatened, some engineers inject microorganisms into the ground that actually consume leaking gas and oils. And on the experimental fringe, uses of trees and molasses have appeared. The sweet syrup activates native bacteria that in turn break down the chemical. Trees such as poplars planted on contaminated sites acquire lead, and can later be cut and removed from sites. Still, methods chosen for cleaning lost urban lands ultimately depend on costs.
Developers have a lot to think about.
They have to control a property. They worry about their liability. And they have to control their cleanup costs.