In situ treatment of dissolved contaminants in groundwater by permeable reactive barrier's (PRB's) has developed as an effective and cost-efficient approach to the remediation and management of contaminated sites over the past decade. PRB's provide passive interception of contaminated groundwater and the destruction or removal of the contaminants by a combination of physical, chemical or biological processes. Steel Slag can be an effective material for use in PRB systems and has demonstrated excellent results in the removal of phosphate, arsenic, and water-born pathogens from groundwater. Based upon steel slag's relatively high levels of calcium and iron, it can often provide the necessary physical and chemical requirements for precipitating the contaminants on site, while allowing the treated water to leave the site within the proper pH limits.