By some estimates, as many as 450,000 urban brownfield sites may exist nationwide. These former commercial or industrial properties can be found in nearly every community where, because of real or perceived contamination, the land sits idle or under-used. Brownfield sites can be as small as a gas station with a leaking underground storage tank or as large as a 100-acre (40.5-ha) abandoned factory containing dumped waste on the site. The sites are not remarketed or reused because owners or operators fear that, if the properties are contaminated, the regulatory requirements to clean them up could be prohibitively time-consuming and expensive. Furthermore, even if such properties were put on the market, developers, and financial credit sources would shun them in part from concerns that dealing with contamination cleanup could raise the costs and slow the pace of reusing the properties.

But the brownfields situation has been changing as local...