Many of the contaminated marine sediment sites under investigation are in shallow coastal areas and are more likely than traditionally studied offshore sediments to be impacted by advective processes such as groundwater flow, tidal pumping, and wave pumping and by resuspension via ship and storm activity. If impacted sediments are to be left 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. Currently, there is no demonstrated, systematic process for measuring and evaluating contaminant transport pathways within sediment systems.
The objective of this project was to provide an approach for determining the relative importance of contaminant transport pathways for coastal sediments, including (1) an integrated suite of measurement techniques to characterize contaminant transport pathways, (2) a corresponding set of indices that quantify the transport phenomenon on a common dimensional scale, and (3) an understanding of the importance of these processes in the risk, fate, and management of contaminated sediments.
Researchers applied an integrated suite of methods for the direct characterization of dynamic contaminant transfer pathways in sediment. Methods for the quantification of mechanisms, magnitudes, and directions of porewater-mediated contaminant transport were integrated with sediment geochemical characteristics, hydrodynamically driven particle transport, and biological processes. These processes are examined together such that they can be ranked and compared to support in-place sediment management.
The measurement suite was fielded at Paleta Creek in San Diego Bay and at Southeast Lock and Bishop Point in Pearl Harbor. The project quantified a range of process-based transport pathways, including diffusive fluxes (combined molecular and bio), advective fluxes, sedimentation fluxes (background and storm), erosion fluxes, and biodegradation fluxes. For each of the 25 contaminants assessed, dominant pathways were determined, and appropriate management approaches were identified.
These tools can be used to quantify and rank contaminant transport pathways within sediment systems. The results can help focus further site studies to the most important or uncertain parameters, improve predictions of exposure risks or recovery rates, and aid in the implementation of in situ remediation, stabilization, and containment strategies.