Background The majority of the around 1.5 million soil-contaminated sites in Europe are polluted with non-ferrous metals. In many cases, this has led to the contamination of groundwater with metals such as zinc, cadmium, cobalt and nickel. In Flanders alone more than 5 000 sites contained groundwater that is contaminated with metals. Currently, the best available remediation technique for groundwater contaminated by non-ferrous metals is to pump it up and clean it in wastewater treatment plants – i.e. ‘pump and treat’ (P&T). However, this is a long and costly operation, which often fails to meet cleanliness standards. It also often has negative effects on the local groundwater balance. Furthermore, the process involves the use of hazardous chemicals and the production of metal-containing waste sludge. Objectives The INSIMEP project aimed to show that treating metal-contaminated groundwater onsite, by accelerating naturally-occurring biogeochemical processes, is a better solution than current techniques. This method, known as in-situ metal precipitation (INSIMEP), is more economical and more environmentally friendly, since the resulting metal concentrations in the groundwater are lower, no hazardous chemicals are required, and no solid waste is produced. The project aimed to demonstrate the technique’s long-term effectiveness and ease the way to its large-scale application by implementing the process on sites owned by the beneficiary itself. Results The INSIMEP project focussed on demonstrating the in-situ method at three of the beneficiary’s sites each with varying contaminant mixtures and hydrogeological conditions. The project successfully demonstrated that the in-situ method resulted in the precipitation of metals to a level below remediation targets: (i.e., Zinc levels of The project results highlight the environmental benefits of the in-situ method: no hazardous chemicals are required, no solid waste is produced, and energy use is lower (in turn entailing lower carbon emissions). The technique’s long-term economic feasibility and effectiveness was also indicated; although initial costs for the in-situ technique are higher, after 10 years it is shown to be more economically feasible with operational costs that are 40% lower than the traditionally used "pump and treat" (P&T) remediation technique. Results of the INSIMEP project are expected to facilitate the large-scale application of the in-situ method in other sites, including at the beneficiary’s site at Zolder at which preparatory activities have already started. The project is expected to contribute to the objectives of the Water Framework Directive (by aiming to achieve "good" surface water and groundwater status by 2015), the Groundwater Directive (by preventing and controlling pollution through appropriate measures) and the Integrated Pollution and Prevention Control Directive (by preventing the further spread of groundwater contamination). Further information on the project can be found in the project's layman report (see "Read more" section).