The Observer, December 2004
Halifax tank shows promise for dispersant tests
BY LISA KA’AIHUE
Project Manager
In chemical dispersant research, there are three general platforms for testing: laboratory, wave tank, and open ocean. This summer, the council was invited to a demonstration of a promising new wave tank near Halifax, Nova Scotia.
Oil is poured into the water for the first demonstration of the new wave tank near Halifax, Nova Scotia. Designed to test chemical dispersants, the tank is a collaboration between the Environmental Protection Agency and the Department of Fisheries and Oceans Canada. The new tank is relatively small, making it easier to change water between tests. Photos by Lisa Ka’aihue, citizens’ council.
Each of the three platforms has its advantages and disadvantages.
Laboratory tests are relatively cheap and repeatable, as they involve only small amounts of oil and dispersant and are performed in small flasks. But they cannot accurately simulate real-world conditions such as wave energy.
Oil is poured into the water (left) for the first demonstration of the new wave tank near Halifax, Nova Scotia. Designed to test chemical dispersants, the tank is a collaboration between the Environmental Protection Agency and the Department of Fisheries and Oceans Canada. The new tank is relatively small, making it easier to change water between tests. Photos by Lisa Ka’aihue, citizens’ council.
Wave tanks are much larger and are used to create waves as an added parameter to dispersion testing. While there is no substitute for open-ocean testing, wave tanks do overcome some of the disadvantages of flask tests.
Occasionally, field experiments are performed in which oil and dispersants are applied to the open ocean. These are rare, however, because of the expense and because of the difficulty of obtaining government permission for a real, if small and controlled, pollution incident.
The council has supported laboratory research to assess chemical dispersant effectiveness in cold water. The next logical step for the council is to consider wave tank testing and start incorporating more open ocean variables such as waves.
The first step in considering wave tank testing is to learn as much as possible about the handful of wave tanks available to perform dispersant testing around the world. There are tanks in Canada, the United States, France and Norway.
The newest tank on the scene is the recently fabricated wave tank facility at the Bedford Institute of Oceanography near Halifax. The tank was constructed as a partnership between the U.S. Environmental Protection Agency and the Canadian Department of Fisheries and Oceans. The council was invited to observe the first demonstration of the tank this summer.
What makes this tank unique is its ability to mimic a wide range of breaking wave energy levels at sea, thus providing the conditions necessary for dispersants to work effectively. Plans to start on a series of efficacy tests were are under way, using Canadian oil products and at least two dispersants. The next phase will focus on toxicity to different organisms, such as herring.
The tank sits on the shore of Halifax harbor and is 60 long by two feet wide. The sea water used in the tank is taken from the Halifax Harbor and pumped through a filter to remove particulate matter. During the demonstration I observed, the water depth was a little over four feet to simulate deep-water conditions.
The tank includes a “bubble ring” used to keep the oil off the sides of the tank during the experiments. Air is forced through a curtain of copper tubing with holes in it. The rising bubbles prevent the oil from coming in contact with the tank walls.
Once the bubble ring was operational, oil was laid on the water, then dispersant was sprayed onto the oil. Next, the wave generator at one end of the tank was turned on. Observers saw dispersion taking place as shown by the coffee-colored cloud forming in the water. But, more importantly, the tank has scientific instruments to measure wave energy and dispersion rates.
The tank was constructed so that it could easily be emptied and filled for multiple experiments. This is a huge advantage over much larger tanks where it is difficult to clean the tank between every experiment.
The council is part of an effort in Alaska to support broad-based dispersant research supported by regulators, industry, academics, and stakeholders. Although the process has not reached a stage of implementing research, wave tank tests are certainly a high priority for all. Judging from this summer’s demonstration, it seems likely the Bedford tank could help answer our questions about chemical dispersants.