R7 PM Uncertainty Analysis in Risk Assessment: Influences on Decision-making
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 327-329

(FRE-1117-841475) Probabilistic Consequence Analysis for Dispersant Use on Oil Spills.

French-McCay, D¹, Whittier, N¹, Rowe, J¹, Aurand, D², ¹ Applied Science Associates, Inc., Narragansett, RI, USA² Ecosystem Management & Associates, Inc., Lusby, MD, USA

ABSTRACT- The implications of chemical dispersant use was evaluated in an objective manner using modeling to inform decision-makers involved in oil spill response planning. There are many possible spill scenarios that could be modeled, as well as an essentially infinite number of potential spill sites where releases could occur. Thus, to evaluate the likely consequences of hypothetical spills, modeling was performed in probabilistic mode, i.e., by randomly varying spill date and time, and so environmental conditions during and after the release among potential conditions that would occur. Spills of commonly shipped crude oils at five representative spill locations in shipping lanes of major US ports (Delaware Bay, Florida Straits, Galveston Bay, San Francisco Bay and Prince William Sound) were modeled with alternative spill response strategies (combinations of mechanical response and dispersant use) to examine potential impacts. The model results were analyzed to estimate mean, standard deviation (SD), and 5th, 50th and 95th percentile results for surface water and shoreline oiling, water column and sediment contamination, and biological impacts. The results of the modeling show larger decreases in wildlife and shoreline impacts with dispersant use than increases in water column effects, supporting the contention that there are more opportunities to save wildlife, shorelines, and near-shore sensitive habitats with dispersant use than there are risks of impacting water column biota. If the areas that would be impacted by surface oil are those where wildlife are concentrated, as they typically are near shore, and the water column impacts resulting from dispersant use would be offshore where water column biota are lower in abundance, the trade-off is more heavily weighted toward dispersant use before oil comes near the shoreline. The results quantify the trade-offs between water-column resource and wildlife/shoreline impacts resulting from dispersant use that may be used in decision making, contingency planning and ecological risk assessments.

Key words: modeling, oil, dispersant, toxicity