In FY-2008, the MMS received a research proposal that identified a multi-year dispersant research program to answer the questions and address the data gaps in the efficacy of dispersants identified in the NRC report. There were seven distinct tasks or projects proposed in this two-year dispersant research programs. In FY-2008, the MMS funded Tasks 1, 2 and 5. These three tasks were completed in TAR project 615. http://www.mms.gov/tarprojects/615.htm.

In FY-2009, the MMS Oil Spill Response Research Team requested a technical and cost proposal update of Task 4  Evaluation of Dispersant Effectiveness in Low-Dose, Repeat Applications and Task 6  Validation of Small-Scale Laboratory Test Dispersant Effectiveness Ranking. The objective of this research program is to continue research and development on the use of chemical dispersants. Two tasks will be addressed. The period of performance would be one year.

Task 4. Evaluation of Dispersant Effectiveness in Low-Dose, Repeat Applications

Conventional wisdom and usual practice for the application of dispersant to large oil spills is through large, fixed-wing aircraft spraying. However, the spray from a single pass from such spray systems can treat a slick of only about 0.15 mm thick at the normal design application ratio of one part dispersant to 20 parts of oil. Thick oil patches accounting for 80 to 90 % of the total oil volume can easily be 10 to 100 times thicker than this. The application rate of dispersant from an aircraft application hitting the thick oil could be in the range of 1:200 to 1:2000 under such conditions. The question to be answered in this project is: Does dispersant applied in very low doses (1:1000 to 1:200) disperse a small fraction of an otherwise dispersible oil or is it simply ineffective until a minimum threshold concentration of dispersant in the oil is achieved, possibly through repeated spray passes?

The answer to this question has significant ramifications with respect to operational decisions in dispersant application on thick oil slicks. For example, if a test spray were completed on a thick oil slick and no dispersion was observed the dispersant might be considered to be in-effective, whereas multiple applications of the dispersant might be necessary to achieve a dosage sufficient to generate dispersion. This work will be completed at two test scales. Initial work will be completed at a laboratory test tank scale to assess the effect of low-dose application on a number of oils. Once trends have been determined in the laboratory testing will be completed at Ohmsett to verify similar behavior at full-scale.

Task 4 involves three tasks.

1. Small Scale Tests
2. Large Scale Ohmsett testing
3. Data Analysis and Technical Report

Validation of Small-Scale Laboratory Test Dispersant Effectiveness Ranking

Bench scale dispersant effectiveness tests are routinely used around the world to rank the potential effectiveness of a dispersant product on standard oils or to study the effect of oil and dispersant type and environmental parameters on dispersant effectiveness. In the United States oils must achieve a measured effectiveness of 45% or greater in the swirling flask to be placed on EPA’s NCP Product Schedule as an approved dispersant. But, what do the effectiveness values recorded in these laboratory tests mean with respect to likely effectiveness in the field and do the bench scale tests fairly evaluate dispersant products? Attempts have been made to correlate the results of bench scale tests to one another with mixed success thus suggesting that few, if any, of the tests are representative of real-world situations.

Very limited field data is available to allow the comparison of bench scale test results to field success and so this has also not been adequately done. It is proposed that the Ohmsett test facility be used as a surrogate to the field to provide “field” effectiveness estimates on a select number of oils for a select number of dispersants. Bench-scale tests would be conducted using the same dispersant and oil combinations and the results compared to establish if the bench-scale test results can be used to provide reasonable estimates of field performance. The EPA Baffled Flask Test (BFT) and the WSL Laboratory test (WSL) will be the bench-scale test methods used in the study. The BFT is being proposed as the new EPA standard and the WSL test has been shown to be more representative of field.

Task 6 involves three tasks:

1. Large Scale Ohmsett Testing
2. Bench Scale DE Testing
3. Data Analysis and Technical Report

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Last Updated: 12/16/2008, 11:48 AM