Background It is estimated that there are approximately 1.5 million contaminated industrial sites in the EU, which could be potential sources of soil and ground water contamination. Some 300,000 sites, including 9,000 in Flanders have already specifically been identified as definitely or potentially contaminated. The major pollutants include mineral oils, heavy metals and organic contaminants such as chlorinated hydrocarbons (CAHs). Such pollutants are present in the groundwater at the Tenneco factory site, long a contaminated by the metal processing activities that started in 1964. These environmental pollutants are carcinogenic, mutagenic and embryotoxic for humans and need to be removed from the ground water. A new technique consisting of the injection of molasses had successfully been applied in the US on a smaller scale, but with lower remediation targets than the proposed LIFE-Environment project. Objectives The beneficiary wanted to remedy the groundwater of its polluted site in Sint Truiden in a cost effective and environmentally sound way, keeping the impact on the ecosystem to a minimum. Tenneco aimed to successfully employ molasses substrate injection as a remediation technique, achieving total removal of contaminants, and demonstrate the technique’s applicability on a larger scale project than had previously been experienced in the US. Specifically, the beneficiary expected that the injection of molasses would result in a significant reduction in the saturated zone of: • chlorinated solvents (including tetrachloroethene [PCE], trichloroethene [TCE], trichloroethane [TCA) and carbon tetrachloride [CT]): on-site 50% in 2005, 80% within ten years, and off-site 75 % in 2005, 99% within ten years • hexavalent chromium (Cr VI) on-site 55% in 2005, 80 % within ten years, and off-site 70 % in 2005 and 99 % within ten years • mineral oil: off-site - no extension of contour mineral oil. More broadly, the project aimed to: • obtain reliable data that could be extrapolated to the whole soil and groundwater remediation industry. • inform, motivate and activate the remediation industry and other relevant actors to change to injection of molasses if appropriate. Results The REHAMOS project was the first European endeavour to attempt large-scale pollution removal via the use of molasses injection. The project successfully demonstrated the benefits of this remediation technique on such a scale and collected extensive data indicating that the injection of molasses had significant environmental benefits - no emissions, no nuisance for surrounding areas - and economic benefits – it was cost effective compared to conventional remediation techniques. These results were disseminated to inform, motivate and activate relevant stakeholders, including through the development of a "Centre of Excellence". Interest from the industry for using this remediation technique is growing: the project even had a significant spill-over effect in influencing other projects to use a similar remediation technique, such as a remediation project involving hexavalent chromium (CrVI) in Lier (Belgium) and involving chlorinated aliphatic hydrocarbons (CAHs) /VOCIs in Hamond-Achel (Belgium) and a soil decontamination initiative in Tessenderlo (Belgium). Full-scale molasses (automated) injection into the aquifer at the Tenneco Automotive Europe site in Sint-Truiden, Belgium, induced a significant reduction of the CrVI and trichlooretheen (TCE) mixed pollution present in the groundwater, by anaerobic bioremediation processes (bioprecipitation of chromium and reductive dechlorination of TCE). The areas that have been treated for the longest periods show almost complete de-chlorination to ethene and ethane (both harmless) and chromium levels. However, many monitoring wells within the plume remediation area still show high levels of dichloroethylene (DCE) and VOC. A cost assessment for different possible remediation techniques was carried out, finding that the applied technique was cheaper than conventional remediation techniques by about a factor of three, and, in addition, with little or no impediment to the neighbouring area (during the remediation of groundwater contamination underneath 100 to 150 homes). Due to the sensitivity of the technique to soil conditions, results indicate that the technique is site-specific and preliminary testing (in the lab and on-site) is still necessary prior to implementing the technique at other sites. Additionally, addressing freezing conditions was an issue during the project's duration. A solution was found to address this issue, though. Using weather forecasts the project injected extra molasses prior to the expected freezing conditions. Costs related to the preparation of the molasses injection are relatively high. Therefore this technique is not advisable to treat small surfaces for CAH contamination; for CrVI this treatment is adapted to small surfaces since the reduction of CrVI to chromium III (CrIII) & precipitate is less sensitive to the risks mentioned above (fewer preparation tests).