A brownfield is a property which was once was home to a viable commercial or industrial operation but, because there is no longer an adequate market demand for that operation, the property sits idle, partially because of possible environmental contamination, waiting for a new function.

It is estimated that there are 500,000 to one million brownfields nationwide, but this number is difficult to confirm and there is reason to believe that the number is higher. Contamination will vary with the nature and size of the commercial or industrial operation that once occupied the site. A large steel plant may have covered more than 200 acres and may have contaminated the soil and groundwater with heavy metals, the concentration of which will be greatest near to the source of contamination and will lessen as the distance from the source increases. A dry cleaning operation or a gas station may cover less...