Background Groundwater is the main source of drinking water in Europe and its contamination by polluted soils or as a result of landfill leaching can pose a major threat to the environment and human health. The Water Framework Directive (2000/60/EC) and the Groundwater Directive (80/68/EEC) stipulate improvements in water and groundwater quality by the year 2015. In recent years, in situ treatment of aquifers has become increasingly beneficial, as the relevant technology develops, becomes more reliable and gains greater acceptance. Objectives The objective of the MULTIBARDEM project was to demonstrate the technical feasibility of a multifunctional permeable barrier, ‘Multibarrier’, which combines different principles of barrier technology, namely the removal of pollutants based on both physico-chemical and biological activities in order to treat plumes with mixed pollutants. The projects aimed to prove that the technology could be a workable alternative to landfill leachate treatment and could offer a more economical means of preventing the risk of groundwater contamination than landfill remediation or re-installation. Multibarrier technology would be applied on a field scale in Belgium and Austria, in two regions of Europe with completely different hydro-geological characteristics, solid-waste composition and operating conditions. Results The MULTIBARDEM project successfully demonstrated three types of ‘Multibarriers’ in different circumstances and set ups. Although for some substances improvements are possible, it can be concluded that Multibarriers can form an effective and efficient way of treating contaminated groundwater. Several technical difficulties needed to be solved in the course of the project (e.g. fast breakthrough of the zeolite) and part of the process (biological removal of ammonia) could not initially be measured due to low temperatures in the first monitoring period (winter 2008). By the end of the project, however, a removal rate up to 70% of ammonia was achieved. Good results have been obtained with the first pilot at Hooge Maey (horizontal configuration) and the pilot at the Pottinger site (although at the latter site the removal of CAH could not successfully be demonstrated). The second pilot at Hooge Maey (vertical configuration) was less successful mainly due to difficulties with the homogeneity of the groundwater flow. The Multibarriers have a high demonstration value. They are a tailor-made technological solution for groundwater contaminated with a mixture of pollutants. The performance of some aspects of the multibarriers have been evaluated on a laboratory scale. Such evaluation in the field are rare, and thus the onsite demonstrations of multibarriers represents a great innovative step forward. Furthermore, many of the processes demonstrated in the multibarriers designed in this project are innovative, including: Classical biological nitrification/denitrification under in situ conditions (12°C); Use of grape mark as slow release C-source in a barrier; Use of zeolites as an in situ buffer with potential for auto-regeneration; Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).