Once implemented, PRBs leave little room for flexibility or modification. The continuous trench system relies on the natural gradient to direct water to and through a trench that has been excavated and filled with reactive material. Regardless of the configuration, a reactive wall that treats groundwater contaminated with chlorinated hydrocarbons and chromium typically contains iron metal. As chlorinated hydrocarbons contact iron metal, they react at the iron surface. Electrons for the process are provided by the corrosion of the iron metal.
Iron affects chromium in a very different way.
Theoretically, any material could be used as the reactive media, depending on the type of contaminants in the groundwater. Promising research is underway on a variety of reactive media. One of the most promising focuses on bioremediation, either by modifying the characteristics of the groundwater or developing reactive media that promote bioremediation, either alone or in conjunction with chemical processes. Numerous design and installation issues affect PRB use, including contaminant concentration, water velocity barrier configuration and emplacement methods. Because the entire plume must be directed through the reactive zone of the barrier, a complete site characterization is critical.