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Cities all over the world are phasing out heavy industrial activities in their urban areas in favour of a safer, more sustainable, mixed-use built form. Consider Pittsburgh, where steel manufacturing was a crucial component of the local economy, and numerous former industrial properties have since been reimagined as vibrant neighbourhoods with a myriad of residential, office, and retail uses. These bygone industrial sites, many of which are characterized by severe soil contamination, are frequently known as brownfield lands.
Brownfield sites do not have to be large in scale. Gas station and dry cleaner operations, which can be and often are located outside designated commercial and industrial areas, typically produce a range of subsurface contaminants. Pesticides and heavy metals like lead and mercury, left unobserved, could also pose community safety risks, though the cost of remediating the soil and making it suitable for future development has been a significant barrier for many builders. In an effort to revitalize these derelict properties, government programs in various jurisdictions have been created to help predict or offset the expense of remediation.
Several techniques are used to clean up contaminated land. Soil vapour extraction involves the drilling of wells into soil situated above the water table. Volatile organic compounds are then vacuumed out of the wells in vapour form. Air sparging — pushing contaminated vapours upward from the groundwater via air injection — may also be used in conjunction with this practice. In some cases, specific deep-rooted plant species like sunflowers are introduced to the site, which can help immobilize and degrade the contaminants. Known as phytoremediation, some species also absorb metals in their tissue, and are disposed of as hazardous waste after maturity.
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