Diluted bitumen in sea water – some basic science

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Author: Northern Gateway
Dated: 6 February 2013

A lengthy discussion on the subject of diluted bitumen’s behavior in sea water took place in Prince Rupert this week at the Joint Review Panel hearings examining Northern Gateway’s marine emergency response planning. The evidence on the record shows that diluted bitumen acts like many other common oil types in water.

There are significant adverse effects when crude oil is spilled in the ocean. This post is not meant to down-play this reality. The post is meant to outline the density science—crude oils, including diluted bitumen are less dense than water and therefore float.

Project opponents have said that diluted bitumen sinks in open water and is therefore next to impossible to clean-up. This isn’t true and there is no evidence on the record to support this claim.

It is important to understand the physical properties of water and oil, because these properties determine how the two liquids will behave when they come into contact.

Dr. Alan Maki, an oil spill response expert testifying at the JRP hearings in Prince Rupert on February 5, 2013, told the hearing, “It's fundamental physics that everything has a specific gravity relative to water. Water is 1.0. All the compounds we're talking about range from .75 up to .92, .93. It is an immutable fact of physics that they will float.”

The products Dr. Maki was referring to are the crude oil products Northern Gateway intends to ship: diluted bitumen and synthetic crude oil. It’s also important to note that sea water’s density is higher than 1.0, more like 1.02. Compounds with densities lower than 1.02 will float. That’s the basic science.

But there are other factors at play here as well. All oils weather when exposed to the environment. Oil’s physical properties are changed by wind, waves, sunlight and other environmental exposures over time. As oil weathers, it can become denser. So what matters is the answer to this question: Does weathered diluted bitumen become denser than sea water?

Some have suggested that diluted bitumen weathers rapidly, with diluent evaporating leaving bitumen behind to sink. This isn’t true. Diluted bitumen does not weather to a pure bitumen state.

Northern Gateway conducted tests to measure the density of weathered diluted bitumen under simulated conditions. At no time during the two-week-long tests, did diluted bitumen weather to a density greater than water. You can read the full report here.

It’s also a fact of reality that pockets of submerged crude oil have occurred when crude oil—and here we’re speaking of all crude oil types including, but not specifically isolated to, diluted bitumen—has been spilled into moving bodies of water like oceans, lakes, rivers and streams.

Water in the ‘real world’ is not plain water. Sediments—sand, silt, biomass, etc.—are often suspended in water because of energetic physical motions like waves.

Have you ever been to a sandy beach that had waves lapping at the shore line? That water, in motion, has the energy needed to lift the fine grains of sand up from the sea bed into the wave and move it about. When crude oil particles and sediment particles combine, together, they can become denser than water and sink. It’s important to understand that this physical interaction isn’t unique to diluted bitumen. Sediment is most prevalent in near-shore, shallow areas, which can be isolated using booms.

Agitation will separate oil from sediment, the oil then floats back to the surface—this has been a successful tactic for cleaning up submerged oil in the Kalamazoo River.

Northern Gateway’s first priority is to ensure that oil is not spilled. In the unlikely event of a spill, Northern Gateway’s world-class, science-based emergency response planning will be there to act quickly to minimize any adverse environmental effects.  

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  • Northern Gateway, Feb 11th, 2013 (2 years ago)

    Hi Nicole, thanks for your question.

    As noted in the post above, when oil combines with sediments, it can sink. This is what happened in Kalamazoo. However, it should be noted that only a small amount of the oil that was released from Line 6B ended up submerged.

    With time and certain water environments, oil weathers and the lighter hydrocarbons release in air. Over time, this increasingly heavy oil can be churned in the water and attach to suspended matter in a river, such as sediment, leaves, or sticks. When this occurs, it becomes heavier than water and sinks.

    During cleanup of the Enbridge leak on the Kalamazoo River, this occurred with smaller pieces or flecks of oil rather than with large areas of oil.

    The vast majority of the oil that flowed into the creek and river was contained and removed by traditional response methods—floating booms to contain and then skimming and vacuuming into tanker trucks. The crude oil did not float on the water surface one day and then sink to the bottom the next day. Rather, with the hot weather, and river at flood stage and turbulent, the sediments were stirring in the high flow of water and light hydrocarbons evaporated. As time elapsed, some oil pulled away from the floating oil and adhered to sediment and debris, eventually causing small and larger clumps to become fully submerged. Much of the cleanup activities in later months have been focused on finding and stirring up these clumps to re-free the crude oil which floats to the river surface to be removed. This continued through the spring of 2012 when the activity required to find and stir up the submerged oil was determined to have reached its effective conclusion and avoidance of further environmental risk.

  • Nicole d'Entremont, Feb 09th, 2013 (2 years ago)

    Why did the oil submerge in the Kalamazoo River?

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