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TECHNICAL REPORTS
Bioremediation and Biodegradation

Transport and Degradation of Toluene and o-Xylene in an Unsaturated Soil with Dipping Sedimentary Layers

^a Dep. of Geology, P.O. Box 1047, Blindern, 0316 Oslo, Norway
^b Dep. of Soil and Water Science, Agricultural University of Norway, P.O. Box 5028, 1432 Ås, Norway
^c NVE (The Norwegian Water and Energy Directorate), P.O. Box 5091, Majorstuen, 0301 Oslo, Norway

* Corresponding author (anne.sovik{at}jordforsk.no)

Received for publication August 20, 2001. A lysimeter trench was established at the Gardermoen delta (50 km north of Oslo, Norway) to study the flow of water and transport and degradation of aromatic jet fuel components (toluene and o-xylene) in the undisturbed unsaturated zone. Site investigations with ground-penetrating radar revealed the presence of dipping sedimentary layers within the foreset unit. This study has shown that the foreset bed of the Gardermoen delta structure provided a preferential flow path for the transport of the solute plumes, but did not have dramatic effects on the degradation potential under the current conditions. The degradation potential for toluene and o-xylene in the unsaturated zone at Gardermoen was very high and almost all of the injected hydrocarbons were biodegraded before reaching the saturated zone. However, the horizontal displacement of the plume showed that knowledge about sedimentary structures in the unsaturated zone is important for a sufficient monitoring of contaminant transport and for remediation purposes. Carbon dioxide and O₂ were measured in situ simultaneously with extraction of water samples, and indicated aerobic biodegradation of toluene and o-xylene. Overall, first-order degradation coefficients were calculated to be in the range of 0.19 to 0.21 d^-1 and 0.10 to 0.11 d^-1 for toluene and o-xylene, respectively.

Abbreviations: BTEX, benzene, toluene, ethylbenzene, and xylene • GPR, ground-penetrating radar