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3F - Coastal Zone Mgnt (WEP/188) Pathways of contaminant transport in nearshore sediments: using field measurements to balance risk and recovery. Apitz, Sabine1, 2, Chadwick, D2, 1 SEA Environmental Decisions, Little Hadham, Hertfordshire, UK2 SSC-San Diego, San Diego, CA, USA ABSTRACT- Many contaminated marine sediment sites currently under investigation are in shallow, coastal areas, much more likely than more traditionally studied offshore sediments to be impacted by processes such as groundwater flow, tidal pumping, wave pumping and by resuspension via ship and storm activity. If impacted sediments are to be managed in place, it is critical to evaluate potential pathways by which contaminants might pose an ecological or human health risk, and to monitor, minimize or eliminate these pathways. On the other hand, the relative importance of these pathways as mechanisms of sediment recovery must also be determined. What are critical to determine are the projected mode and/or mechanism of toxicity that is of concern, and whether transport processes increase or decrease these risks; whether the relative rates of recovery and exposure are balanced out in a protective way. In a multi-institutional program, methods for the in-place quantification of mechanisms, magnitudes and directions of porewater-mediated contaminant transport have been integrated with sediment geochemical characteristics, hydrodynamically driven particle transport, and biological processes. These contaminant transport pathways have been measured in the field, and results have been put into equations that allow for the generation of common time indices for these processes, and thus an identification of predominant pathways. Ranking and quantifying these pathways on the basis of time-scale has the advantage of allowing disparate processes to be compared by the same standard, and also provides a framework for communicating important information such as the time required for natural recovery, or the expected life-span of a containment strategy. Field results, and how they may be used to balance risk and recovery scenarios, will be discussed. Key words: contaminant transport, sediments, risk/recovery, PRISM |
