A permeable reactive barrier (PRB) is a passive, in-situ remediation technology used to treat contaminated groundwater. PRBs are constructed using reactive materials, which are installed perpendicular to the direction of groundwater flow, to intercept and treat the contaminated groundwater as it flows through the barrier. PRBs can be designed to target a variety of contaminants, including metals, organic compounds, and nutrients. Common reactive materials used in PRBs include zero-valent iron (ZVI), activated carbon, limestone, and biological media, such as compost or mulch. The selection of the reactive material is dependent on the specific contaminants of concern and the hydrogeological properties of the site. As the contaminated groundwater flows through the PRB, the emplaced materials react with the contaminants to either immobilize, transform, or remove them from the groundwater when supplemented with a treatment mechanism such as biodegradation.