Quantifying Tradeoffs – Net Environmental Benefits of Dispersant Use

Abstract

ABSTRACT Oil spill response often involves making decisions regarding dispersant usage; the potential tradeoffs of increasing exposure of water column biota to hydrocarbons in order to reduce surface and shoreline oiling needs to be carefully considered and justified. A modeling analysis using RPS ASA's Spill Impact Model Application Package (SIMAP) was performed to evaluate the likely water volume adversely affected by naturally- or chemically-dispersed oil, as well as the surface area impacted by floating oil, and summarized in guidance useful for response planners and decision-makers. Key inputs were varied: oil type, oil volume, environmental (e.g., wind speed, temperature) conditions, dispersant use, weathering state when dispersants are applied, and toxicity to aquatic biota. Model results, including water volume where acute toxic effects would occur and the area of water surface oiled (which would impact wildlife, as well as socioeconomic uses), are summarized in tabular form, as well as a software-tool for interpolation, to provide data for quantitative comparisons of tradeoffs. Findings show that for (effective) dispersant treatment of floating oil volumes up to 100,000 gal in a single location during a short period of time (<1 hr; e.g., by a dispersant plane sortie), the area of surface water where water column biota would be affected would be much less than that affected by floating oil thick enough to directly affect wildlife. Thus, even if large volumes of oil are dispersed, a net environmental benefit may be achieved due to reduction or prevention of exposure to floating and shoreline oil, especially if the dispersant applications are over a wide area or over time.