The Metal Problem
Highly toxic and highly soluble metals are contained in numerous waste streams including those from power, chemical, electronics facilities, general manufacturing plants, and mining facilities. Lead, chromium, arsenic, zinc, cadmium, copper, and mercury are the most common metal contaminants found on remediation project sites (US EPA, October, 2000). Cyanide is a common inorganic contaminant as well. Metal concentrations in excess of established health guidelines have been shown to create significant health risks to humans.
Past Remediation Options
In the past, conventional remediation of soil impacted by heavy metals has relied on excavation, which was expensive and disruptive. In addition, moving the soil only moved the problem, without treating the soil or reducing the long-term liability. For groundwater, pump and treat remediation relied on pumps to remove groundwater from the aquifer through a series of extraction wells or trenches. The extracted water was then treated above ground or disposed of off-site. Pump and treat methods fail to address the source of the contamination in the vadose zone. Although the construction of passive permeable treatment walls containing zero valent iron filings can reduce some metals to less toxic varieties, the passive barriers are expensive and do not treat source areas (Thomasser and Rouse. 2001).