Assessing Sydney Tar Ponds Remediation and Natural Sediment Recovery in Nova Scotia, Canada

摘要

Background. Sydney Harbour, Nova Scotia, has long been subject to effluent and atmosphericinputs of metals, polycyclic aromatic hydrocarbons (PAHs), and polychlorinatedbiphenyls (PCBs) from a large coking operation and steel plant that operated inSydney for nearly a century until closure in 1988. Contaminated effluents from the industrialsite resulted in the creation of the Sydney Tar Ponds, one of Canada’s largestcontaminated sites. Since its closure, there have been several attempts to remediate thisformer industrial site and finally, in 2004, the governments of Canada and Nova Scotiacommitted to remediate the site to reduce potential ecological and human health risks tothe environment. The Sydney Tar Ponds and Coke Ovens cleanup project has become themost prominent remediation project in Canada today.Approach. As an integral part of remediation of the site (i.e., which consisted of solidification/stabilization and associated capping of the Tar Ponds), an extensive multiplemedia environmental effects program was implemented to assess what effects remediationhad on the surrounding environment, and, in particular, harbour sediments.Additionally, longer-term natural sediment recovery rates of select contaminants predictedfor the harbour sediments were compared to current conditions. During remediation,potential contributions to sediment quality, in addition to remedial efforts, were evaluatedwhich included a significant harbour dredging project, propeller wash from harbour traffic,storm events, adjacent loading/unloading of coal and municipal wastewater treatmentdischarges. Two sediment sampling methodologies, sediment grab and gravity corer,were also compared to evaluate the detection of subtle changes in sediment quality.Results. Results indicated that overall spatial distribution pattern of historical contaminantsremains unchanged, although at much lower concentrations than previouslyreported, due to natural recovery. Measurements of sediment indicator parameter concentrationsconfirmed that natural recovery rates of Sydney Harbour sediments were in broadagreement with predicted concentrations, in spite of ongoing remediation activities.Overall, most measured parameters in sediments showed little temporal variability evenwhen using different sampling methodologies, during three years of remediation comparedto baseline, except for the detection of significant increases in total PAHconcentrations noted during one year of remediation monitoring. The data confirmed theeffectiveness of mitigation measures implemented during construction relative to harbour