Pilot study Biswurm: steam-air injection in fractured sandstone

The thermally enhanced in-situ remediation technique of steam-air injection is currently tested under difficult geology formations in a fractured sandstone aquifer. On behalf of the community of Villingen-Schwenningen VEGAS designed the feasibility study for six months of operation to treat approximately 1500 m³ of soil and sandstone.

The aim of the pilot trial is to confirm the technical feasibility and the efficiency of steam-air injection for the simultaneous remediation of the saturated and vadoze zone. The determination of the thermal range of influence in the saturated fractured bedrock and the results of heat propagation as well as the contaminant removal during the field trial shall lead to the design and cost estimation of a thermally enhanced soil remediation of the contaminants TCE, PCE and Toluene from the hot spot.

The pilot study covers approximately an area of 75 m² located in the centre of the contaminant hot spot (800 m²) on the site of a former communal incineration facility. The concentrations of CHC, BTEX and mineral oils of the affected groundwater and soil vapour range from hundreds of micrograms to several milligrams per litre of water and air. The pilot is financed one third respectively by the community of Villingen-Schwenningen, the state of Baden-Württemberg and the research programme of SAFIRA II of the Helmholtz-Center for Environmental Research (UFZ) Leipzig. Moreover it is supported by the environmental agency (LUBW) and the regional council located in Freiburg. The UFZ provides his modular and mobile thermal remediation unit MOSAM, which was specially designed by VEGAS to carry out such pilot studies within R&D projects.

Steam-air injection combines the remediation techniques of soil vapour extraction, Air-sparging and steam injection. Organic contaminants located in the fractures of the sandstone aquifer and unsaturated zone will be evaporated. The major mass of contaminants is removed in gaseous form by the soil vapour extraction from the unsaturated zone. Condensing steam along the fractures may heat the bed rock by heat conduction and will desorb impregnated contaminants from the sandstone. The gaseous contaminants transport is controlled by the air injection rate. More than 10% of mass portion of air in the injected steam-air mixture should minimize the risk of a liquid organic phase transport in the fractures.

After 3 months of operation the heat and steam front propagation is distinctively horizontally oriented for all three levels of injection. This indicates a horizontal orientation of the fractures at the bottom of the aquifer, on heights of the groundwater table and in the unsaturated zone. The conductive heat transfer of the bed rock is characterized by an average temperature increase of 0.4 K/day meaning a maximal remediation time of almost 200 days to reach the eutectic temperature by heat conduction.

So far, according the heat and steam front propagation as well as contaminant extraction behaviour the applicability and remediation of the fractured sandstone aquifer by steam-air injection was confirmed. Folgeprojekt: Stadt Villingen-Schwenningen Altlastensanierung Altablagerung ehem. städt. Verbrennungsplatz, Sanierung mit Dampf-Luft-Injektion: Wissenschaftliche Beratung und Begleitung der DLI Sanierung

Koschitzky, Hans-Peter

Trötschler, Oliver

VEGAS

From: 2008-11-23

To: 2009-12-31

Helmholtz-Zentrum für Umweltforschung GmbH - UFZ
Stadt Villingen-Schwenningen, Stadtbauamt, Abt. Boden und Wasser
Projektleiter AG: Prof. Dr. Holger Weiß Martin Bittens (UFZ)
Bernd Lidola (Stadt VS)