AROMATIC HYDROCARBON CONTAMINATION OF CLAY STRATA BELOW A PETROCHEMICAL SITE, UK Organic Contaminant Migration in Clay Aquitards

摘要

Clay units have often been assumed to provide good protection for underlying aquifers from contamination. This assumption, however, is rarely proved. The capacity of clays to resist contaminant invasion in urban areas is of significant interest, especially where underlying aquifers are used for supply. We report the initial findings of an on-going field study to investigate organic contaminant penetration of clay strata below a former petrochemical site in the UK. The clay is a thin, relatively continuous unit 6-7.5m below ground surface within a shallow sandy aquifer contaminated with aromatic hydrocarbons (benzene, toluene, ethylbenzene, and styrene). Concentration/ depth profiles were obtained from cores at four locations and demonstrated transport of aromatic hydrocarbons into the clays with significant penetration in places. Preliminary modelling suggests that the clay penetration cannot always be explained by simple diffusion; advective transport through preferential pathways appears probable. Clay thin sections indicate the presence of palaeo-root holes and worm burrows. These potentially explain the enhanced solute penetration, and suggest that the presence of unconformities should be considered when assessing the protection afforded by thin clay beds.