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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Thermal In-situ Remediation of the Unsaturated Zone by Steam Injection - Final Presenation - "

In the late 1960s a disposal site for hazardous wastes containing chlorinated solvents and galvanic sludges was opened in a forest near Mühlacker. The wastes were deposited within a layer of silty loam which was considered to be impermeable enough to protect the subsurface underneath from being contaminated by the leachate of the waste site. Nevertheless, by the late 1970s, contaminants had migrated through the unsaturated zone below which consists of highly heterogeneous weathered sandy marl and were detected in the underlying keuper gypsum aquifer 30 m below ground surface. Detailed site investigation lead to the conclusion that separate phase contaminants (mainly TCE) were retained by a capillary barrier intersecting the unsaturated zone at a depth of 15 m below ground surface.
Soon after that the site was included in the model site program (\"Modellvorhaben\") funded by the state of Baden- Württemberg and remediation activities started. The site was encapsulated by sheet piles and an asphalt cover was placed on the surface to reduce the leachate flux from the deposited waste. Remediation of the deposited waste itself and the groundwater zone was conducted as well as conventional soil vapour extraction in the unsaturated zone. Due to the complex nature of the subsurface, in-situ remediation of the unsaturated zone by means of conventional methods was ineffective. To enhance contaminant removal a thermally enhanced remediation scheme was installed in a section of the site where steam can be injected in the highly contaminated zone between 7 and 15 m below ground surface. The total volume of soil to be treated in the target area is approximately 3000 m3.
The pilot plant was operated by the two companies Züblin Umwelttechnik GmbH and Preussag Wassertechnik GmbH and VEGAS from the University of Stuttgart, who conducted the scientific oversight. The pilot study was funded by the \"Kommunaler Altlastenfonds\" and the city of Mühlacker, represented by the consultant company Weber-Ingenieure GmbH.