Geostatistical Analysis of PCB-Contaminated Sediment in a Commercial Dock, Swansea, UK

Abstract

Dredge materials are now regarded as a resource and are being promotedfor beneficial uses such as beach, saltmarsh and wetland restoration.Such a variety of end-uses requires more complex risk assessments,particularly with regard to contaminant loadings and their likely fatein sensitive receiving environments. A case study of Polychlorinatedbiphenyl (PCBs) concentrations in the sediments of a large (1.5 km x 0.5km) industrialised dock is used to explore sampling issues and theiranalysis using geostatistics. A nested sampling scheme of 101 sites isused to identify the magnitude and scale of spatial variation ofsediment PCBs. Experimental variograms of individual congeners, totalPCBs, particle size, total organic carbon and their principal componentsare computed and modelled. These provide a clear description of thespatial structure of PCBs and some insight into possible processesaffecting their distribution. Ordinary kriging is used to estimate PCBconcentrations over the dock. Two areas in the dock exhibit elevated PCBconcentrations, which might reflect particular point sources ofcontamination. The results confirm the effectiveness of the sampling fordetecting the spatial scale of variation, and the suitability ofgeostatistical techniques for investigating the processes controllingthe spatial distribution of contaminants. Accurate description of thespatial distribution of contaminants can reduce the risk ofmisclassification of material designated for remediation, disposal orbeneficial use.