In-Situ-Hydraulic Soil Washing of a Diesel/HEL-Damage on a Tank Farm Site

Pollutants were adsorbed in the unsaturated soil zone as well as in the currently saturated, prior to 1979 unsaturated (due to the previously lower groundwater table), soil zone. First investigations began in May 2000 and resulted in the identification of an initial damage pattern and a first groundwater remediation concept. The following September an existing oil tank and the surrounding contaminated soil were excavated, after which a drifted contamination, starting from the pump room in direction of the groundwater flow, was detected. Next steps were the installation of barrier wells near the border of the neighbouring parcel to avoid more drifting and to limit lateral damage. After finishing the detailed groundwater remediation concept, remediation started in June 2001. In April 2003 an additional groundwater investigation was performed to determinate the extension measure of the damage. According to the investigation results it can be stated that the main contamination took place in the sixties and seventies in the pump room, and migrated through the unsaturated soil zone especially in a W and NNE direction. Due to the groundwater flow direction, the pollutants spread prior to 1979 to the SSE and afterwards to the NE in the upper soil zone layers. The vertical limitation was determined to be 8 m below the surface at the center of contamination and 5 m in the downstream area.