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Quarterly Journal of Engineering Geology & Hydrogeology

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A preliminary investigation of the release of oil from contaminated clays and other fine-grained sediments during consolidation

^{1 1}School of Human & Environmental Sciences, PO Box 227, Reading University, Whiteknights,Reading RG6 6AB, UK (e-mail: d.m.thornley@reading.ac.uk)
^{2 2}Solutions to Environmental Problems (PTS Ltd), Millfield House, Leintwardine, Herefordshire, SY7 OLB,UK

Fine-grained sediments on land, or in a freshwater or marine environment, may become contaminated with a wide range of pollutants including hydrocarbons. This paper is concerned with preliminary studies of the mobilization and transportation of hydrocarbons, during the process of consolidation, to adjacent sediments or water bodies. A modified Rowe Cell was used to measure the consolidation properties of prepared kaolinite and bentonite clay–water slurries, with and without the addition of oil, along with hydrocarbon-bearing drill-cuttings samples taken from the sea-bed adjacent to two North Sea oil-well platforms. The consolidation properties of the kaolinite and bentonite clay slurries were little altered by the addition of oil, which was present at concentrations of between 8073 and 59 572 mg kg^–1. During each consolidation stage, samples of the expelled pore-fluids were collected and analysed for oil content. These values were very low in comparison with the original oil concentration in the samples and changed little between each consolidation stage. Analysis of the slurry samples both before and after consolidation confirms that, proportionally, little oil is removed as a result of consolidation. The implication of these results is that, for the range of samples tested, the very high hydraulic gradients and particle rearrangements that occur during the process of consolidation are capable of releasing only proportionally small amounts of oil bound to the fine-grained clay and silt particles.

Key Words: clay • consolidation • environmental impact • polluted water • sediments