A brownfield is land that was previously used for industrial or commercial purposes and that has known or suspected contamination including of the soil or groundwater due to hazardous wastes. Examples of former uses include factories, dry cleaning establishments, oil refineries, landfills and gas stations. Common contaminants include gasoline, oil, pesticides, solvents, asbestos, lead and other heavy metals.
Brownfields contrast with greenfields, which are land that is in its natural condition or that is used for agricultural or parks. It can be very expensive to remediate brownfields, especially to make them suitable for residential use, depending on the type(s) and extent of contamination. However, it is often preferable to reuse remediated brownfields for new purposes rather than building on greenfields because it keeps more land in its natural state and can allow housing and activities to be kept closer to urban centers, thereby minimizing transportation costs.
Because of the vast numbers of brownfields and the impossibility of remediating them all within the span of a few years, or even a few decades, in situations where the contamination is not too severe and is not affecting adjacent properties or causing air pollution (for example, from the emission of volatile organic compounds), a good strategy can be to reuse a brownfield without major remediation, at least temporarily, as parkland, for industrial or commercial purposes, or for the generation of solar or wind energy.