Securing the N65 OMV Zwölfaxing landfill contaminated site

The contaminated site N65 OMV is a landfill in Zwölfaxing containing waste generated by an oil refinery from 1961 onwards. Deposits include acid resins and acid tar, fuller's earth and carbonate sludge. The contaminated site has a volume of approximately 80,000m³ and a surface area of 38,000m². Analyses showed that the contaminated site was affecting the groundwater. According to the hazard assessment and priority classification, pollutant dispersion is relatively localised, but the pollutant potential is very high.

Groundwater monitoring wells were installed to determine the exact spread of pollutants on the site. Once the position of the oil lens on the groundwater had been established, the Specialist Civil Engineering department started work.

A jet-grouted cut-off wall was created in the groundwater fluctuation zone with the aid of a baffle. Additional stabilisation of the acid tar was achieved with the dredger using the baffle’s slurry return line.

Further measures included boring three oil skimming wells. These will allow the floating oil to be extracted from the soil. The site will then be sealed and secured from above by IAT with a surface seal made from bentonite mats. Special infiltration systems will be used to drain off the surface water.