A permeable reactive barrier (PRB) is a zone of reactive material placed underground to intercept and react with a contaminant plume in ground water. Typically, PRBs are emplaced by replacing soils with reactive material in a trench cut through a contaminated ground water aquifer. PRBs can also be installed above ground to provide access to the treatment media. Above ground systems are also referred to as ground water treatment cells.
PRBs can be installed using several methods including trenching or through injection wells. Treatability studies are typically conducted to evaluate the performance of reactive materials to treat ground water under site-specific conditions. Selection of material for the barrier is based on results of these treatability studies. Computer modeling is used to simulate the complex chemical reactions that occur in a PRB.
The material in the barrier is permeable, which allows the ground water or contaminant plume to flow through the barrier. When the targeted contaminant encounters the reactive material in the barrier, a chemical reaction occurs with the barrier material that results in adsorption, mineral precipitation, or degradation to a harmless compound. Reactive barriers that do not incorporate motors or mechanical devices are considered passive treatment.
PRBs are widely used to control organic contamination in ground water; however, less effort has been made to apply the technologyto metal and radionuclide contaminants. This technology may be more cost effective than pump-and-treat methods.
The U.S. Department of Energy (DOE) installed PRBs at several Legacy Management (LM) sites. Installation of a PRB hydraulically downgradient of the Monticello, Utah, millsite was completed June 30, 1999, as an Interim Remedial Action. DOE also installed a PRB in October 1995 to treat ground water from a uranium mill tailings disposal site at Durango, Colorado. In addition to operating the PRBs, ESL personnel conduct tests and help evaluate performance at other PRB sites, such as Cotter Corporation’s Cañon City site in Colorado.