Working on behalf of Nortel Ltd., Golder Associates has installed Europe's first reactive barrier treatment system located in Belfast, Northern Ireland. Golder Associates was retained by Nortel to assess soil and groundwater contamination at a number of their sites across the UK. The investigation of the Monkstown facility in Belfast found the groundwater to be contaminated with up to 390 mg/l of trichloroethylene (TCE). Previous owners of the site had used chlorinated solvents while manufacturing electronic components. Years of spillages had resulted in an intense but localized plume close to the current site boundary.

Reaction vessel being installed at Monkstown.

The site is underlain with glacial till interbedded with lenses of silts, sands and gravel. The sand and gravel lenses are sufficiently permeable to allow off-site migration of dissolved solvents. This migration is constrained by the specific orientation of the permeable lenses which themselves contain discrete clay or clayey silt lenses.

During the investigation, the Golder Associates team collected groundwater samples which underwent column reaction experiments conducted by Environmetal Technologies Inc., using iron filings. Test findings indicated that a relatively long pathlength was required to completely reduce the chlorinated solvents. The proximity of the boundary negated this possibility. In response, Golder Associates devised a reaction vessel concept which elongated the reactors pathlength by diversion vertically through a cylindrical column of iron filings. The result? A final column of some six metres in length.

Groundwater was collected using a funnel positioned approximately perpendicular to the flow path. The funnel was created by placing a cement-bentonite wall in a V shape to a depth of around 12 metres. The reactor was situated at the apex of this wall to act as the permeable reactive gate. Reactor sand piles were then located at points downstream and upstream. Arms from the reactor vessel were pushed into these sand piles to form the collection and distribution arms.

Monitoring results on the device installed early in 1996 have been very encouraging. Data shows a 99.97% reduction in TCE levels and daughter products through the reaction vessel. The iron filings have created a strongly reducing environment instigating reductive dechlorination of the chlorinated solvents, thus producing chloride and chlorine free hydrocarbons.

In addition to the positive results, the reactive treatment system offers many benefits in comparison to other methods. The technology requires no power input and can be installed in remote areas, operating costs are minimal; there are no effluent treatment costs and all chlorinated solvents are treated. Further, it is estimated that the overall cost of this system is around 25% to 33% of the installation costs for an extraction system which would have had to run for a number of years.