Rocky Flats Test Site

SITE first evaluated the performance of Permeable Reactive Barriers (PRB) technology in 1998 at three locations at the Rocky Flats Environmental Test Site (RFETS) in Colorado. These projects were a cooperative effort between RFETS and the Department of Energy, with support from EPA's National Risk Management Research Laboratory.

PRBs are typically trenches filled with reactive media that are placed in the path of groundwater contaminant plumes. Reactive materials used in PRBs include zero-valent metals, such as iron, and chemicals, such as oxygen or hydrogen, which enhance natural biodegration of contaminants by microbes or other organisms in the subsurface. Contaminants that come into contact with the PRB are removed via chemical reaction or biodegration, or are physically immobilized through adsorption to the PRB.

At RFETS, a major contaminant present at all three demonstration locations was tetrachloroethylene, also called perchloroethylene (PCE), a volatile organic compound (VOC). EPA regulates PCE in public drinking water supplies and has established a maximum contaminant level (MCL) at 5 parts per billion (pcb). PRBs were installed at three separate areas possessing different types of contamination:

• The Mound Site: trichloroethylene (TCE) and PCE from leaking drums filled with lathe coolant
• The East Trenches: contaminated with TCE, PCE and other chemicals from stored wastes that leached into soil and groundwater
• The Solar Evaporation Pond: liquid waste with low levels of radioactivity and high levels of nitrates

The results showed contamination levels following PRB treatment fell to below MCLs and, with minor exceptions, have remained so since. The potential human health and economic benefits that could result from PRB deployments nationwide in similar geologic environments are estimated at:

• Between 1,151 and 13,817 cancers avoided each year in the US
• Cost savings of between $10 million and $1.2 billion associated with avoidance of lethal and non-lethal cancers can be realized
• Operating costs of PRBs are lower than a pump-and-treat system typically used for treatment of standard contaminant plume