Dispersant Use Impact Assessment and Decision Making
Chemical dispersants are one of the many response tools available to decision makers and first responders. The decision to utilize dispersant on an oil spill hinges upon the expected level of resource injury; mainly, the likely water volume adversely affected by dispersed oil and dissolved hydrocarbons, and the surface area impacted by floating oil.
ASA conducted research investigating the tradeoffs regarding the application, or not, of dispersants. ASA’s Spill Impact Model Application Package (SIMAP) physical fates, exposure and oil toxicity models were used to estimate impacts. Variables investigated included oil type, weathering state, oil volume, environmental conditions (e.g., wind speed, temperature), dispersant use, and aquatic biota sensitivity. Model results were presented as water volume where acute toxic effects would occur and the area of water surface oiled (which would impact wildlife, as well as socioeconomic uses).
The results, compiled as part of a project funded by the Coastal Response Research Center (CRRC) at the University of New Hampshire, have been synthesized into an Oil Spill Impact Guide (OSIG) which consists of a full report (currently under review), a hand-held field guide, and a Microsoft Excel-based dispersant use calculator (available below). All of these materials are designed to be used by decision makers and first responders in the field.
This example page from the OSIG Field Guide shows that when dispersant is applied within 12 hours of a spill, impact to water column organisms increase and wildlife impacts decrease with increased dispersant application (blue lines); however impact to water column organisms are nearly removed if the dispersant is applied after 24 hours (pink lines).
- OSIG Components:
- Report – describes the full procedure including the rationale for the variables used, the limitations of the model, and the full recommendations given the results. The report can be downloaded from the CRRC website: http://rfp.crrc.unh.edu/projects/viewProject.php?PROJECT_ID=28
- Field Guide – presents the results from the cases with the largest impacts and summarizes the trade-offs. This document is designed to be small and waterproof, easily stashed on board response vessels.
>> Download the Field Guide - Dispersant Use Calculator – allows the user to input parameters specific to their situation and reports results based on the full set of results. Allows for a comparison of impacts (i.e. the user can compare the impacts of a case where dispersant is applied and not, side-by-side).
>> Download the OSIG Dispersant Use Calculator (Beta version)
For a synopsis of results please see the article in our February 2010 Newsletter.
Draft versions of the field guide and the Excel calculator are available here for download. As these are draft versions, comments and suggestions are welcome to improve their usability. Please contact us with comments or suggestions regarding these tools.