Remediation of chromate contaminated groundwater by a new design of a permeable reactive barrier

For remediation of chromate contaminated groundwater an innovative new design of a Permeable Reactive Barrier (PRB) has been installed in Willisau, Switzerland. The new construction consists of two parts: a single and an offset placed double array of piles (as opposed to a conventional continuous barrier) filled with a mixture of reactive grey cast-iron shavings and gravel. The treatment of the contaminants takes place both within the piles and in the dissolved iron plume generated downstream of the barrier. Groundwater and reactive material was sampled by a Multi-Port Sampling System (MPSS) over a time span of three years. Results from a large 3-D hydrogeochemical dataset show that the double array of piles successfully treats the chromate contamination. The remediation by the single array is not effective enough. The low amount of precipitated secondary phases observed reduces the risk of clogging the system and suggests a favorable longevity of the barrier.