Brownfields are abandoned, idled, or under-used industrial and commercial facilities where expansion or redevelopment is complicated by real or perceived environmental contaminations.

In city planning, brownfield land, or simply a brownfield, is land previously used for industrial purposes, or certain commercial uses, and that may be contaminated by low concentrations of hazardous waste or pollution and has the potential to be reused once it is cleaned up. Land that is more severely contaminated and has high concentrations of hazardous waste or pollution, such as Superfund or hazardous waste sites, does not fall under the brownfield classification.

Note that in the United Kingdom and Australia, the term applies merely to previously used land. See below.

The term "brownfields" first came into use on June 28, 1992, at a U.S. congressional field hearing hosted by the Northeast Midwest Congressional Coalition. Also in 1992, the first detailed policy analysis of the issue was convened by the Cuyahoga County Planning Commission. The U.S. EPA funded its first Brownfield pilot project in 1994. The term has been in common use in other countries since about 1975{cite web|url=http://dictionary.reference.com/browse/brownfield}}

Barriers to redevelopment of brownfields

Many contaminated brownfield sites sit idle and unused for decades because the cost of cleaning them to safe standards is more than the land would be worth after redevelopment. However, redevelopment of brownfield sites has become more common in the first decade of the 21st century, as developable land grows less available in highly populated areas. Also, the methods of studying contaminated land have become more precise, and techniques used to clean up environmentally distressed properties become more sophisticated and established.

Many federal and state programs have been developed to assist developers interested in cleaning up brownfield sites and restoring them to practical uses. Some states and localities have spent considerable money assessing the contamination present on local brownfield sites, to quantify the cleanup costs in an effort to move the brownfield redevelopment process forward.

In the process of cleaning contaminated brownfield sites, surprises are sometimes encountered, such as previously unknown underground storage tanks (USTs), buried drums or buried railroad tank cars containing wastes. When unexpected circumstances arise, the cost for cleaning up the brownfield land increases, and as a result, the cleanup work is either delayed or stopped entirely. To avoid unexpected contamination and increased costs, many developers insist that a site be thoroughly investigated (via a Phase II, Site Investigation or Remedial Investigation) prior to commencing remedial cleanup activities.

Innovative brownfields redevelopment strategies

A number of innovative financial and remediation techniques have been employed in recent years to expedite the cleanup of brownfield sites. For example, some environmental firms have teamed up with insurance companies to underwrite the cleanup of distressed brownfield properties and provide a guaranteed cleanup cost for a specific brownfield property, to limit land developers' exposure to environmental remediation costs and pollution lawsuits. The environmental firm first performs an extensive investigation of the brownfield site to ensure that the guaranteed cleanup cost is reasonable and they will not wind up with any surprises.

After the "Dot-Com Bust" of 2000, many venture capital firms looking for new businesses in which to invest in brownfields. Venture capital investments in brownfield-related businesses have included companies developing new cleanup technology, companies that do remediation and development projects in brownfield lands.

Innovative remedial techniques employed at distressed brownfield properties in recent years include bioremediation, a remedial strategy that uses naturally occurring microbes in soils and groundwater to expedite a cleanup, and in situ oxidation, which is a remedial strategy that uses oxygen or oxidant chemicals to enhance a cleanup. Often, these strategies are used in conjunction with each other or with other remedial strategies such as soil vapor extraction. In this process, vapor from the soil phase is extracted from soils and treated, which has the effect of removing contaminants from the soils and groundwater beneath a site. Some brownfields with heavy metal contamination have even been cleaned up through an innovative approach called phytoremediation that utilizes deep-rooted plants to soak up metals in soils into the plant structure as the plant grows. After they reach maturity, the plants -- which now contain the heavy metal contaminants in their tissues -- are removed and disposed of as hazardous waste.

Research is under way to see if some brownfields can be used to grow crops, specifically for the production of biofuels.http://www.anrcats.msu.edu/press/070106/071006_brownfields.htm Michigan State University, in collaboration with DaimlerChrysler and NextEnergy, has small plots of soybean, corn, canola and switchgrass growing in a former industrial dump site in Oakland County, Michigan. The intent is to see if the plants can serve two purposes simultaneously: assist with phytoremediation, and contribute to the economical production of biodiesel and/or ethanol fuel.

Post redevelopment uses

Some state governments restrict development of brownfield sites to particular uses in order to minimize exposure to leftover contaminants on-site after the cleanup is completed; such properties are deed-restricted in their future usage. Some legally require that such areas are reused for housing or for new commercial use in order not to destroy further arable land. The redevelopment of brownfield sites is a significant part of new urbanism. Some brownfields are left as green spaces for recreational uses.

For historical reasons, many brownfield sites are close to important thoroughfares such as highways and rivers; their reclamation can therefore be a major asset to a city. Portland, Oregon, has pioneered the use of road and rail infrastructure to support the cleanup and reuse of brownfield sites. Another example is the Atlantic Station project in Atlanta. In Seattle, rusted remains of a gas factory were left in place to add character to Gas Works Park.

But one of the most well-known areas in the United States for brownfield redevelopment is Pittsburgh, Pennsylvania, which has successfully converted numerous former steel mill sites into high-end residential, shopping and offices. Several examples of brownfield redevelopment in Pittsburgh include the following:

In Homestead, Pennsylvania, where the site once occupied by Carnegie Steel has been converted into a successful commercial center, The Waterfront.

In Pittsburgh's Squirrel Hill neighborhood, where a former slag dump for steel mills was turned into a $243 million residential development called Summerset at Frick Park.

In the Southside (Pittsburgh) neighborhood, where a former LTV steel mill site was transformed into Southside Works, a mixed use development that includes high-end entertainment, retail, offices, and housing.

In the Hazelwood (Pittsburgh) neighborhood, where a former Jones and Laughlin steel mill site was transformed into a $104 million office park called Pittsburgh Technology Center.

In Herr's Island, a 42-acre island on the western bank of the Allegheny River, where a former rail stop for livestock and meatpacking were transformed into Washington's Landing, a waterfront center for commerce, manufacturing, recreation and upscale housing.

Regulation of brownfields

In the United States, investigation and cleanup of brownfield sites is largely regulated by state environmental agencies in cooperation with the EPA. Many of the most important provisions on liability relief are contained in state codes that can differ significantly from state to state http://www.ncsl.org/programs/environ/brownfields/brownfields.htm. The EPA, together with local and national government, can provide technical assistance and some funding for assessment and cleanup of designated sites, as well as tax incentives for cleanup that is not paid for outright (specifically, cleanup costs are fully deductible in the year they are incurred http://www.epa.gov/brownfields/bftaxinc.htm.)

In the United Kingdom, brownfield land and contaminated land are seen as discrete concepts in terms of government policy and the law, though of course a given piece of land may be both at once. The more formal term for brownfields is "previously developed land" (PDL), the definition of which talks of it being vacant, derelict or underused. It may not have been industrial in the past, and it may or may not be contaminated.

The government has a target that 60% of new housing development must be on PDL, and the overall aim in this crowded country is to recycle PDL in preference to taking greenfield sites.

In England, government agencies like the Regional Development Agencies and English Partnerships help secure and support the regeneration of run-down areas including those hit by industrial decline and dereliction, and market conditions. Contaminated land is dealt with as a separate issue, both through the development control system (concerned to ensure contaminated land is made suitable for its new use) and by Part IIA of the Environmental Protection Act of 1990 (which looks at land in the context of its current use).

Both regimes are concerned with the risk that the presence of contaminants may pose to human health or the environment, and ensuring that risk is identified properly and managed down to acceptable levels. Under Part IIA, each local authority must inspect its area for "contaminated land" as defined by the Act, and where it is found must secure its remediation, with the original polluters first in line to pay where these can be found, in line with the 'Polluter Pays Principle'. Please see http://www.defra.gov.uk/environment/land/contaminated/index.htm for the relevant law and policy and links to related policy areas in the UK.

Brownfield land that has been left to naturally re-vegetate is often of high nature conservation interest — much more so than equivalent agricultural land — due to the presence of early successional habitats. A number of invertebrate species are associated with such sites, for example the Dingy Skipper butterfly, and these have suffered dramatic declines in recent years due to losses in brownfield sites due to development and regeneration.