Field Monitoring of a Permeable Reactive Barrier for Removal of Chlorinated Organics

The application of zero-valent iron (Fe0) in the funnel-and-gate permeable reactive barrier (PRB) installed at the Vapokon site, Denmark, was conducted in 1999 to remediate the groundwater contaminated by chlorinated aliphatic hydrocarbons (CAHs). Over the past 4 years, except in September 2002 and January 2003, about 92.4–97.5% CAH removal could be achieved with the PRB. Although there was a continuous decrease in total alkalinity (90.3%), calcium (81.7%), and sulfate (69.2%) ions in the groundwater crossing the PRB, probably caused by mineral precipitation and resulting in 0.88% porosity loss per year, no noticeable deterioration of the barrierʹs performance was observed between March 2000, and August 2003. Instead, climatic variation in the barrierʹs performance on CAH dechlorination was examined. The dechlorination rates in the cold season (January 2003 and March 2000) were generally smaller than those in the hot season (August 2003, September 2000, and September 2001). Besides, 1,2-dichloroethane and dichloromethane, which were proven to be not treatable by Fe0, could also be removed with the PRB, thereby suggesting enhancement from Fe0 adsorption or microbial degradation.