Final Activity Report Summary - MOD-PRBNA (Biogeochemical transport modelling of groundwater remediation based on a permeable reactive barrier and natural attenuation) Permeable reactive barriers (PRBs) are used to clean-up polluted groundwater by creating favourable conditions for degradation of pollutants by micro-organisms. The objective of the project was to improve our knowledge on the performance of permeable reactive barriers. The project has resulted in a better understanding of the operation of permeable reactive barriers under realistic groundwater flow regimes and biogeochemical conditions. A model was developed based on the existing PHT3D code, that couples groundwater flow to the pertinent chemical and biological reactions in the barrier. Lab-scale model simulations suggest that the long-term efficiency of iron barriers is mostly determined by decreases in iron reactivity (due to mineral precipitation), and that decreases in porosity are less important. The model for PRBs is now available with a user-friendly excel interface and can be used to design future PRBs, to test the performance of the barrier and to evaluate the longevity of the technology.