A permeable reactive barrier, or "PRB," is a wall constructed below ground to clean up contaminated groundwater. The wall is "permeable," which means that contaminated groundwater can flow through the PRB to be treated. The reactive materials that make up the wall either trap harmful contaminants or make them less harmful. The treated groundwater flows out the other side of the wall. PRB has emerged as a promising and sustainable in situ groundwater remediation technology, which has the advantages of low maintenance costs, service longevity, and in situ treatment of a variety of groundwater pollutants (e.g., heavy metals, inorganic and organic pollutants).