Under the proposed U.S. Coast Guard rulemaking, assets to treat spills in U.S. waters with chemical dispersant will be available within 12 hours after the spill in areas that have pre-approval plans. This increased availability of chemical response assets will likely result in more frequent consideration of dispersants as a response option for all spills, including those closer to shore and in shallow waters. If dispersant application becomes a required capability, it will be necessary to implement methods and procedures to ensure the readiness of response equipment and supplies for dispersant use, similar to the requirements for mechanical response equipment.
This question addresses environmental and operational effectiveness. Currently, it is not possible to predict the overall field effectiveness of dispersants for a spill event, a critical aspect of the trade-off analysis. Resource trustees need to be able to evaluate the benefits of reduced loadings of oil on shoreline habitats and smaller slicks that threaten water-surface resources compared to increased risks from dispersed oil plumes on water-column and benthic resources. Both potential risks and potential benefits depend on the effectiveness of dispersant application, particularly in nearshore settings. Better information is needed to determine the window of opportunity and percent effectiveness of dispersant application for different oil types and environmental conditions. Currently, dispersant effectiveness is a user input to fate and transport models, but potential effectiveness should be estimated by a physical-chemical efficiency model that integrates all of the complex processes controlling oil weathering and oil entrainment into the water column. Furthermore, there is no standard definition of field effectiveness and how it should be reported.
Relevant state and federal agencies, industry, and appropriate international partners should develop and fund a research program that provides the data necessary to predict, through modeling of the chemical, environmental, and operational conditions, the overall effectiveness of a dispersant application, specifically including conditions representative of nearshore physical settings. Two general types of modeling efforts and products should be recognized: (1) output intended to support