Publication Abstract

Risk assessment of PCB-contaminated dock sediment using geostatistical techniques.

J. Reed, A. Chappell, J.R. French, and M.A.Oliver

Dredged materials are now regarded as a source of material for environmental improvement and are being promoted for 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 fate in sensitive receiving environments. A case study of Polychlorinated biphenyl (PCBs) concentrations in the sediments from a large (1.5 km x 0.5 km) industrialised dock was used to explore sampling issues and their analysis using geostatistics. A nested sampling scheme of 101 sites was used to identify the magnitude and scale of spatial variation of sediment PCBs. Experimental variograms of individual congeners, total PCBs, particle size, total organic carbon and their principal components are computed and modelled. These provide a clear description of the spatial structure of PCBs and some insight into possible processes affecting their distribution. Ordinary kriging was used to estimate PCB concentrations throughout the dockyard sediments. Two areas in the dock exhibited elevated PCB concentrations, which might reflect particular point sources of contamination. The results confirm the effectiveness of the sampling regime for detecting the spatial scale of variation, and the suitability of geostatistical techniques for investigating the processes controlling the spatial distribution of contaminants. Accurate description of the spatial distribution of contaminants can reduce the risk of misclassification of material designated for remediation, disposal or beneficial use.

Reference:

J. Reed, A. Chappell, J.R. French, and M.A.Oliver. 2002. Risk assessment of PCB-contaminated dock sediment using geostatistical techniques. Management of Contaminated Sediment: 129-136