The transport behaviour of creosote and coal tar in Severn Estuary alluvium
This thesis presents the results of research undertaken into the transport behaviour of\ud coal carbonisation by-products (coal tar and creosote) in alluvial deposits in the\ud Severn Estuary, UK.\ud Coal tar, and its derivative creosote, comprise viscous multi-component hydrocarbon\ud liquids with a low aqueous solubility. A number of former industrial sites located on\ud the Severn Estuary have been investigated. The geology beneath these sites\ud comprises deposits of alluvial clay in excess of 10m thickness with subordinate peat\ud bands. These deposits are conventionally assumed to be of low permeability.\ud However, hydrocarbon contamination has been observed within and beneath the clay\ud strata.\ud Characterisation of alluvial deposits found the clay component to be dominated by\ud silicate mineralogy. The alluvial clay typically has a low organic carbon component\ud whilst subordinate peat horizons contains much higher levels of organic carbon.\ud Detailed logging of alluvial soils identified vertical to sub-vertical fossil root\ud structures penetrating the soil matrix. This network of macro-pores provides a\ud preferential transport pathway for Dense Non-Aqueous Phase Liquids (DNAPLs).\ud Organic Carbon Partition Coefficents (Koc) were derived for the polynuclear\ud aromatic hydrocarbon phenanthrene, which is a principal component in coal tar and\ud creosote, to alluvial clay and peat. The Koc values were consistent with those\ud reported by other authors for natural soil organic carbon.\ud In the absence of water, creosote is wetting of alluvial clay,\ud The soil matrix of alluvial clay has a low permeability and the fossil pore structures\ud present a significantly higher permeability pathway. Soil sampling and preparation\ud can significantly disturb the root structures in the soft alluvial deposits, leading to\ud misleading geotechnical parameters.
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