Permeable Reactive Barriers (Proceedings of the International Symposium held at Belfast, Northern Ireland, March 2004). IAHS Publ. 298, 2005, 12-22.

1 Department of Civil Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

2 Environment & Resources DTU, Technical University of Denmark, Lyngby, Denmark

Abstract A funnel-and-gate permeable reactive barrier (PRB) packed with zero valent iron (Fe⁰) was constructed at Vapokon site, Denmark in September 1999 to remediate the groundwater contaminated by chlorinated aliphatic hydrocarbons (CAHs). In order to understand the variation of the performance of the PRB over the past 4 years and identify the major factor(s) affecting the iron barrier’s performance, comprehensive monitoring of the behaviour of the Fe⁰ PRB was conducted between March 2000 and August 2003. Although there was a continuous decrease in total alkalinity (90.3%), calcium (81.7%) and sulphate (69.2%) ions in the groundwater across the PRB, probably caused by mineral precipitation and resulting in 0.88% porosity loss per year, no noticeable trend of deterioration of the barrier’s performance was observed. Virtually, over the past 4 years, about 92.4–97.5% removal of CAHs from the groundwater could be achieved across the PRB, except in September 2002 and January 2003. Instead, climatic variation of the barrier’s performance on CAHs dechlorination was examined in which the dechlorination rates in cold season (January 2003 and March 2000) were generally smaller than those in hot season (August 2003, September 2000 and September 2001). The high DO content in the groundwater caused by the recharge from rainfall precipitation may also be one of the factors affecting the performance of PRB on CAHs dechlorination.

Key words chlorinated aliphatic hydrocarbons; climatic variation; funnel-and-gate; Vapokon site; zero valent iron