Performance assessment and monitoring of a permeable reactive barrier for the remediation of a contaminated site

The present study illustrates the long-term monitoring plan carried out in order to investigate the performance of a zero-valent iron permeable reactive barrier (PRB) at a chlorinated solvents’ site. The cleanup intervention has been undertaken at an industrial landfill located near the city of Turin (Italy) and represents the first full-scale application of this technology in Italy. The monitoring plan started in November 2005 with the aim to verify the attainment of the cleanup goals and to evaluate the efficiency status of the PRB. Controls focuses not only on contaminant monitoring but also on the hydraulic and chemical conditions created by the barrier, in order to evaluate potential long term effects of secondary biogeochemical processes (e.g. mineral precipitation, microbiallymediated redox transformation, gas accumulation) on PRB performance. The monitoring plan provides controls on groundwater chemistry (target contaminants and geochemical indicators) and core sampling for mineralogical analysis of zero-valent iron by X-ray diffraction and scanning electron microscopy. The first, partial results of the monitoring activity are illustrated. Monitoring data clearly indicate that the plume is being adequately captured and treated in order to accomplish the clean-up goals with a good safety margin. However, it results that mineral precipitation and gas phase accumulation could determine, over time, a decreasing in hydraulic conductivity and porosity of the barrier, thus modifying the flow field through the reactive cell. Besides the monitoring controls, further investigations will be performed to assess the occurring microbial process and to evaluate their impact on PRB performance