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OSRR-476-Ohmsett 2003 Cold Water Dispersant Effectiveness Experiments

Project Number
Project Initiation Date
Performing Activity
S.L. Ross Environmental Research, Ltd.
Principal Investigator
Mr. Randy Belore
Contracting Agency

During the past two years there has been an increased use of dispersants as a response technique to offshore marine oil spills. The U. S. Environmental Protection Agency has recently revised the National Project Schedule with regards to dispersants, and the cold water application and performance of these materials has come under critical review.

MMS sponsored two series of dispersant effectiveness (DE) experiments at Ohmsett - The National Oil Spill Response Test Facility, in Leonardo, NJ., to evaluate the effectiveness of Corexit 9500 and Corexit 9527 dispersants on Alaskan and Canadian crude oils. These crude oils have a wide range of physical and chemical properties and were tested in fresh and in weathered conditions.

During both series of DE experiments, MMS hosted groups of approximately 40 observers from government, industry, academia and the private sector who participated in all aspects of the actual testing program.

This project was conducted in two separate testing phases. Phase 1 was conducted

Between February 25 and March 14, 2002 at Ohmsett (Project 450). Phase 2 was conducted in February 2003 at Ohmsett.

The identical crude oils used in the Phase 2 DE experiments at Ohmsett were also tested for their in-situ-burning capabilities (Project 452). The in-situ-burn experiments were conducted October 21 - November 1, 2002 in the Alaska Clean Seas portable wave tank at the BP Fire Training Grounds, Prudhoe Bay, Ak. Results and final reports from the in-sit-burn experiments are found under Project 452. When both set of experiments are complete, we will have a direct documented comparison of how each crude oil responds to burning and to the use of dispersants.

Latest progress update

In Phase 2, a total of fourteen large-scale dispersant effectiveness experiments test were completed at the Ohmsett facility with various combinations of oil type and dispersant-to-ratio (DORs). The Ohmsett tank water temperature stayed between -0.4 to -1.8C throughout all of the experiments without the need to use artificial chilling. This was due to the unusually cold weather experienced during the test period. Average air temperatures during each test ranged from 2.8 to -7.4C., and the average wave amplitude for the tests ranged between 5.9 and 8.6 inches and the average period was between 1.8 and 2.2 seconds.

A total of about 70 liters of dispersant was sprayed into the 10 million-liter tank during these experiments. The concentration of dispersant in the water at the end of the experiments was about 7 ppm. The dispersant added to the Ohmsett tank water during the test program did not affect the results of experiments; dispersant concentrations of the order of 400 ppm are the lowest at which dissolved dispersant in the water begins to affect dispersant effectiveness test results.

The chemically dispersed runs resulted in high percentages (75 to ~ 100%) of oil dispersing into the water column, with the exception of tests 10 (evaporated NorthStar) and 14 (evaporated Endicott). The dispersant effectiveness trends identified in the smaller scale testing were mirrored in the large-scale test results. The heavily evaporated NorthStar and evaporated Endicott crude oils were resistant to chemical dispersion in both the small-scale and Ohmsett experiments. A higher percentage of the fresh Endicott crude oil was dispersed in the Ohmsett experiment when compared to the small-scale results (74% vs 20 to 30%). This may be due to additional mixing energy present in the Ohmsett tests, in the form of breaking waves that do not develop in the small tanks.

Phase 2 of this project was successfully completed in March 2003. The final report was accepted and distributed in September 2003. A CD ROM is available that contains the final report along with 30 second video clips of all dispersant effectiveness experiments.

Phase 1 of this project was successfully completed in March 2002, (Project 450). The final report was accepted and distributed in August 2002. The final report is available electronically. A CD ROM is available that contains the final report along with 30 second video clips of all dispersant effectiveness experiments.