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Oil Spill Dispersants: Efficacy and Effects
dated since the first design. However, it is very important to document actual oil concentrations under dispersed oil slicks, to validate dispersed oil model predictions and document actual exposures to sensitive resources. Monitoring would also support evaluation of the effectiveness of dispersant applications. NOAA and USCG should develop updated SMART protocols and consider adding a detailed standard operating procedure (including instrument calibrations and data quality objectives) for each sampling and analytical module.
D.5WILL THE EFFECTIVE USE OF DISPERSANTS REDUCE THE IMPACTS OF THE SPILL TO SHORELINE AND WATER SURFACE RESOURCES WITHOUT SIGNIFICANTLY INCREASING IMPACTS TO WATER-COLUMN AND BENTHIC RESOURCES?
This trade-off analysis is the most difficult step of the process because of the lack of quantitative tools to predict the fate and effects of the dispersed oil plume and the benefits associated with less surface oil. It is also one of the most critical questions needing answer for adequate and appropriate decisionmaking. As discussed in Chapter 2, current ecological risk assessment (ERA) workshops on dispersant decisionmaking use a very qualitative approach that is difficult to apply to nearshore conditions where the potential impacts are not easily characterized. For instance, in offshore settings, one might reasonably assume that there is only a small likelihood that organisms on the seafloor may be exposed to significant concentrations of dispersed oil. Such assumptions may not be reasonable in some nearshore settings. Resource trustees need better information on the likely exposure regime, the mechanisms of toxicity of dispersed oil, and appropriate endpoints.
Oil trajectory models for dispersed oil plumes could be valuable tools to predict exposure, but they are incomplete in terms of their representation of the natural physical process involved, verification of the codes, and validation of the output from these models in an experimental setting or during an actual spill. As discussed in Chapter 4, the ability of models to predict the concentrations of dispersed oil and dissolved aromatic hydrocarbons in the water column with sufficient accuracy to aid in spill decisionmaking has yet to be fully determined.
As discussed in Chapter 4, one of the most significant weaknesses in correlating laboratory-scale and mesoscale experiments with conditions in the field results from a lack of understanding of the turbulence regime in all three systems. Likewise, one of the biggest uncertainties in computer modeling of oil spill behavior (with and without dispersant addition) comes from specifying horizontal and vertical diffusivities. It is very difficult to integrate all interacting transport and fate processes and oil