Field-scale investigations of natural attenuation processes on a tar oil contaminated site at a wood preservation facilty - A case study

The Wülknitz wood preservation facility is one of four pilot sites in the thematic network KORA,¹ dealing with tar oil contaminations in aquifers. At this site, tar oil and salt impregnation has been carried out for more than 100 years, resulting in a high level of contamination by tar oil components (BTEX, PAHs and NSO-heterocyclics) throughout the aquifer. However, the length of the contamination plume is only about 300 m. The site is located in northern Saxony (Germany), and the hydrogeological site characterisation is typical of Pleistocene aquifers in Central Europe. A highly permeable aquifer consisting of Quaternary glaciofluvial sand and gravel with a thickness of up to 30 m is characteristic for this site. The contamination plume was mapped in detail by direct push methods. In addition, a monitoring network orientated towards the centre line of the contamination plume and control planes were designed, and so the spatial distribution of contaminants is quite well known. The temporal distribution of the contaminants is characterised by some variability, which probably results from anthropogenic changes in the groundwater's direction of flow. In order to investigate this influence, probes for the continuous measurement of the groundwater level, pH, Eh, temperature and conductivity were installed. The hydrogeochemical background and the relatively short contamination plume led to the hypothesis that considerable microbiological degradation processes occur. Laboratory-scale experiments and long-term on-site investigations were carried out to study microbial processes and their kinetics in detail. These results were compared with field-scale data to verify actual mass flux reduction according to the natural attenuation concept.