Background Numerous European companies - from metal processing to dry cleaners - generate significant amounts of groundwater contamination with chlorinated aliphatic hydrocarbons (CAHs). CAHs are volatile organo-chlorine C1 and C2 compounds that are toxic and carcinogenic. Since they degrade slowly, they form large groundwater plumes that are very difficult to remedy. Traditional remediation techniques - such as pump and treat - are often inadequate, time-consuming, expensive, and put a heavy burden on the environment through excessive water usage, secondary wastes, high energy use, and so on. Anaerobic dechlorination by soil microorganisms is a promising remediation approach for CAH plumes if conditions are favourable or can be engineered to become favourable. Recent pilot-scale research indicates that it is possible to introduce the microorganisms necessary to create favourable conditions in contaminated subsoil by simple groundwater transfer. Using this bio-augmentation (BA) technology in the laboratory has enabled bioremediation in 50% of the cases in which it was not previously possible. However, the technique has never been used in Europe for a full-scale application. Objectives The main objective of the BACad project is to demonstrate the feasibility and cost-effectiveness of full-scale bioaugmentation (BA) for the remediation of a significant CAH groundwater contamination at the project’s location, the Punch Metals site. CAH groundwater contamination at the site is estimated at 500 000 m3 and this contamination has migrated about 1 km off-site, underneath a forest, reaching a depth of 50 m. The beneficiary aims to remediate this groundwater contamination by CAHs in a cost efficient and environmentally sound way, while keeping the impact on the ecosystem as low as possible. While feasibility tests at lab-scale have indicated that the conditions for engineered bioremediation are not optimal (i.e., injection of an organic substrate induces only partial dechlorination), the introduction of suitable bacteria through BA however could induce full dechlorination. This BA technique aims to directly tackle the contamination of groundwater by CAHs. The project aims to reduce the off-site contamination by 50% after five years and 80% after 10 years. Other expected results include improved environmental performance compared with traditional remediation techniques: 70% less electricity use; 50% less water consumption; A reduction of waste streams by 60%; 50% cost savings; and 35% time savings. A key sub-objective is to develop a methodology to transfer the bacteria in the field from already inoculated injection wells to new injection wells. This would avoid the costs involved in growing the bacteria in a laboratory or purchasing new batches each time they were needed. The beneficiary will disseminate the results to key target groups to encourage further treatment of groundwater contaminated with CAH. These include contaminating companies, the remediation industry, research institutes and policy makers. It is anticipated that the results of the project may be used to remediate other CAH contaminated sites using full scale bioaugmentation in Europe.