A layman’s guide to the behaviour of diluted bitumen in a marine spill

Having listened to the arguments for and against the Energy East and the Trans Mountain Expansion (TMX) projects one of the things that really struck me was the low quality of the scientific knowledge used in the debates. In particular, few presenters understood how diluted bitumen behaves when spilled in a marine environment. The intention of this post is to provide a layman’s guide to what the technical literature says on the topic.

Now if you are an activist then you don’t have to read this post. That is because you already “know” that “diluted bitumen sinks”. How do you know this? Because the good people at DeSmogCanada told you so. For those interested in the actual science; here are three documents that will give you a solid initial understanding of the topic. From Canada we have the Environment Canada technical report on the topic:

Properties, Composition and Marine Spill Behaviour, Fate and Transport of Two Diluted Bitumen Products from the Canadian Oil Sands.

From the US we have the National Academies of Science (NAS) report on the subject:

Spills of Diluted Bitumen from Pipelines: A Comparative Study of Environmental Fate, Effects, and Response (2016)

And finally for comparison purposes we have a very recent Royal Society of Canada (RSC) report:

The Behaviour and Environmental Impacts of Crude Oil Released into Aqueous Environments (2015)

The RSC document is not solely about diluted bitumen, per se, but about how all crude oils behave when spilled in aqueous environments. Readers can look at it to determine if dilbit is anything special.

Now the vast majority of the activists I have spoken with like to refer to the US study. It is very funny how parochial Canadian activists can be. They seem to have a base belief that work done in the United States must, by definition, be superior to anything done in Canada. This, however, is far from the truth. You see, the NAS report was intended to address a regulatory purpose and not a scientific one. They didn’t design any experiments; conduct any practical studies; or do any hands-on research. The NAS report represents a state-of-the-literature report that was intended to address a regulatory requirement governing “spill response planning, preparedness, and clean-up”. Because of the nature of their report the authors made a number of inferences (best guesses for the non-technical) that apparently were then run through a political filter that considered the “practical and policy aspects of our [their] recommendations” prior to publication. That is not how science is supposed to be carried out in the scientific community. It is, however, how it is done in the highly-politicized world of US politics and energy regulations.

An examination of the NAS report (and more importantly its list of references) shows that virtually all of the recent practical (in situ and in-lab) results are derived from a limited number of technical papers, the most prominent being the Environment Canada report and a number of original papers prepared by the good folks at Fisheries and Oceans Canada; especially the research group headed by Thomas L. King (no relation). The rest of the NAS report consists of examinations of older work and policy recommendations which, in my opinion, give insufficient weight to the actual science while relying too heavily on speculation based on the general chemical characteristics of the substance. As I pointed out in my previous post on this subject:

My initial expectations were shattered as the literature I had on hand (which was only about 5 years old) made a lot of assumptions that have been overtaken by the most recent literature (the Environment Canada Technical Report).

That is to say, the recent research results demonstrate quite conclusively that depending solely on general chemical characteristics will leave you completely on the wrong side of the current state of the science when it comes to diluted bitumen. The chemistry of these complex mixtures is still too confusing to trust basic theories based on general features like the presence of selected functional groups. As such, the remainder of this post will rely on the actual research conducted by people with budgets to get their hands dirty and test the substances under consideration. Because I have already reviewed much of that original research, the next section of this post is mostly made up from an earlier blog post I prepared on dilbit spills which I wrote when I first evaluated the Environment Canada technical report. For referencing purposes any physical data/observations in the next few paragraphs are straight out of the Environment Canada technical report, although I will add some additional details (which are referenced).

Let’s start with the basics, what is dilbit? Dilbit consists of a mixture of 20% to 30% diluent and 70% to 80% bitumen. The bitumen is exactly what you think it is and the diluent is typically a light-hydrocarbon mixture (like naptha) called “condensate”. The condensate has a specific gravity in the 0.6 g/mL to 0.8 g/mL range and the resultant dilbit has density/specific gravity that ranges from around 0.92 g/mL to about 0.94 g/mL. Since we know that freshwater has a density of 1 g/mL and that seawater density ranges from 1.025 g/mL to 1.033 g/mL that means that when spilled any dilbit will initially float. I’m saying nothing new here. What is new is what happens as the diltbit weathers. Historically it was believed that as the dilbit weathered the diluent would all evaporate away and the resulting evaporated mass would sink. Well, the research says that this is not the case.

Laboratory studies by Environment Canada show that even with a 26.5% evaporation rate (thus with pretty much all the diluent evaporated) the resultant evaporated dilbit still retains a specific gravity (at 0oC) of 1.021 g/mL. Thus the material would not sink in marine spills, as we were previously led to believe, but would actually remain afloat. More interestingly, when lighter oils are hit with breaking waves they form small droplets that lack the buoyancy to float and will often remain entrained in the water column. The dilbit did not act in this way. Rather when the experimental dilbit was exposed to the wave pool, it formed much larger droplets which they called “oil balls” that quickly resurfaced and coalesced into a surface slick. This actually makes dilbit easier to skim off the surface early in a spill event.

The Achilles heel of the dilbit, however, appears to be sediments in the water. Oils exposed to silty water will form oil-particle aggregates (OPAs) which under certain conditions will sink to the bottom. Remember the DeSmogCanada report? This is what they are talking about. In the Environment Canada research when they mixed the spilled dilbit with high concentrations of a very fine type of clay called “kaolin” virtually all the bitumen either dispersed or formed OPAs and sunk to the bottom of the wave tank. Similarly, when the bitumen was exposed to very high concentrations of diatomaceous earth the same thing happened. When the dilbit was exposed to sands, however, the OPAs were not formed and the material instead formed droplets that were highly resistant to sinking and floated strongly on the surface.

Now what the good people at DeSmogCanada failed to apparently understand is that concentrations of clays and silts that high are not typically seen in Canadian nearshore environments. As Environment Canada pointed out, in the Burrard Inlet spill of 2007 virtually no OPA was formed. So while the intertidal zones were badly oiled, the subtidal marine harbour sediments were virtually unaffected by the spill.

Modelling exercises have been done by Fisheries and Oceans Canada using our local conditions and for the approximate sediment load and characteristics of the Douglas Channel. The result was a conclusion that approximately 20% of the diluted bitumen would form oil-particle aggregates which would sink below the sea surface, with little of that material actually sinking to the sea bottom. Coincidentally, that is pretty much the same behaviour one would expect from a typical crude oil spill. A stochastic model of an oil spill in the Salish Sea suggests that the majority of the oil would stay on the surface, and accumulate on the shoreline, rather than dispersing into water column. Once again a spill would be a tragedy, but the behaviour of the diluted bitumen would be no different from a similar crude oil spill.

Now in freshwater environments the effects will not be nearly as clear-cut. Since freshwater is less dense than seawater whether the bitumen will sink or float becomes far more dependent on the source material and ambient temperature. As the NAS study indicates highly-weathered Cold Lake Blend will retain a density less than 1 g/mL (it will float) while Access Western Blend will reach a density above 1 g/mL (it will sink). We also have to consider environmental conditions. Consider the Kalamazoo spill which occurred during a heavy rainfall event where the river was filled with sediments. In that case the events conspired to produce a scenario where a huge percentage of the material formed OPAs and sank to the bottom. What is most interesting about that case is that under those conditions a typical crude oil spill would likely have behaved in a very similar manner. At those sediments levels OPAs were inevitable.

To conclude this post I want to make something abundantly clear. Any oil spill, be it crude oil or diluted bitumen, represents a tragedy and catastrophe (after all consider that the Fisheries and Oceans model of a Salish Sea spill determined that most of the spilled material, not captured by the recovery efforts, would “accumulate on the coastline”). The point of this blog post, however, is to establish whether a diluted bitumen spill would be a uniquely catastrophic situation. Since that is what the anti-pipeline activists fighting Energy East and TMX keep insisting. In response to that question the answer is clear: diluted bitumen does not represent a singular, existential threat to the environment.

This fact is very important because when we are talking about Energy East and TMX we are not talking about a scenario where we either have or do not have oil being transported. Rather we are talking about whether we have Canadian oil or foreign oil transported and how it is moving. The refineries in St John and Quebec still need raw materials to operate, and those raw materials are being shipped via tankers that run through Canadian coastal waters and, for the Quebec refineries, down the St. Lawrence River. Similarly, the oil that supplies the refineries in the Puget Sound has been coming via tankers through the Salish Sea for 20+ years. Both Energy East and TMX will also displace a lot of oil currently being transported by rail.

What the research clearly indicates is that dilbit is not uniquely dangerous to the environment, rather the research says the opposite: that dilbit in a marine environment behaves in a very similar manner to crude oil. As discussed in the research, dlibit is slightly stickier than crude so forms OPAs slightly more effectively than crude. This means that in high sediment environments dilbit will likely sink a bit faster than other crudes. But as a consequence of its stickiness dilbit does not disperse into the water column as readily as some crude oils, instead it forms bigger, more buoyant oil balls that are less likely to be broken up by ocean surfs and are more readily recoverable from the surface.

I will say this again (because I cannot say it enough) any oil spill is to be avoided which means we should be shipping oil in the safest manner possible. On the topic of spills there is one fact upon which all the references agree. For convenience I will simply quote from the RAS:

the overall impact of an oil spill, including the effectiveness of an oil spill response, depends mainly on the environmental characteristics, the conditions where the spill takes place and the speed of response.

Ultimately the government of British Columbia’s point in this discussion is critical. Any increase in the volume of oil transported, be it crude or diluted bitumen, should only occur if it is accompanied by a significant increase in resources for oil spill planning and response. Having plans in place and the resources to carry out those plans immediately at hand will make all the difference in the case of a spill be it diluted bitumen, crude oil or even bunker fuel from a passing freighter.

Author’s note: I have edited the section on the NAS as a regular reader suggests I was being too harsh about it. In my original version I called it: “re-hash of the Canadian work with a lot of guesswork attached” . My re-write clarifies that the NAS was a report aimed at a regulatory purpose and lacked the original content of the Canadian work. My apologies if anyone was offended by the original wording.

Author’s Note 2: Having re-read the introduction I now feel it was a tad harsh and so have cleaned it up to be less adversarial. The intention of this post is not to be political but simply to be factual. My apologies for those insulted by the earlier introduction.

This entry was posted in Canadian Politics, Chemistry and Toxicology, Energy East, Oil Sands, Pipelines, Trans Mountain, Uncategorized. Bookmark the permalink.

26 Responses to A layman’s guide to the behaviour of diluted bitumen in a marine spill

  1. mgaudet34 says:

    Thank you Blair, I very much appreciate your posts and your efforts in getting the truth out there, albeit a daunting task. Your posts are always relevant and backed up with facts and research, something that is in very short supply with the vocal minority of people apposed.


  2. Thank you for your posts. I only found your blog recently and am getting a lot from it.

    I have found one typo to fix:

    the resultant evaporated dilbit still retains a specific gravity (at 0oC) of 1.021 mg/L.

    . (Emphasis added.) I think you mean g/mL; that specific gravity would make the evaporated dilbit perfect for filling party balloons.


  3. CriticalThought says:

    The federal report used 10g/L while noting that it varies from ~1g/L to 48.4g/L. They note that 10g/L is a sediment load and the results show that dilbit sinks under that load. Why did they not conduct studies under lesser sediment loads for more common sediment loads, ie. 1g/L?

    It’s accepted through several studies which you yourself quote that the dilbit is unlikely to sink, unless it encounters heavy sediment loads like those found nearshore ie, where the emulsion is washed ashore similar to Burrard Inlet. Stating that dilbit won’t sink is a bit too dismissive don’t you think, as such a statement does not account for wind and current dispersal of spills into nearshore environments. I mean… sinking dilbit into marine sediments is certainly a concern but so too is where the currents may take the oil that doesn’t sink. Correct me if I’m wrong, but I believe several official statements have been made clear that BC lacks the ability to deal with oil spills off its coast. So, before shipping the product doesn’t it make sense to have the means to deal with a spill first and not the other way around?


    • Doug mackenzie says:

      “…have a means to deal with a spill first….” There is an issue with spending real effort and resources on a problem that is very unlikely to occur. As a pertinent example, all ships have fuel tanks, those fuel tanks might rupture, but does any harbour refuse ships because the harbourmaster lacks the ability to clean up a fuel spill ? the answer is no. The harbourmaster needs a bigger firefighting pump way more than he needs some specialty oil slick cleanup gear.


    • pwlg says:

      I am surprised that the author did not recognize the heavy sediment load of the Fraser River during the late Spring and Summer months. The sediments reach the eastern shores of Galiano Island. English Bay is not the only body of water that could be impacted by a spill. But even in the south-western waters of English Bay have considerable Fraser River sediment in the late Spring and Summer months. As well, the Strait of Georgia is not always a calm piece of water. Winter storms often cause a cancellation of BC Ferries operations due to rough seas. These rough seas can cause heavy oil to disperse and break up and the research conducted in a tank in Saskatchewan was not in the opinion of the Royal Society conclusive and in their words requires more study. Research conducted by the International Tanker Owners Pollution Federation showed heavy crude reaching shorelines in 48 hours and in heavy seas with waves, winds and current flows, the heavy crude can break up and make conventional means of oil spill response ineffective. The ITOPF indicated only 10% of heavy crude oil spills are recovered. The use of dispersing agents, the world class solution according to our politicians, would make matters worse leaving fire as a way to “contain” a bitumen spill before it sinks below the surface. The Enbridge disaster in Michigan provided valuable information. Studies conducted by the US EPA and NOAA as well as from private researchers funded by the industry found the following evidence…

      “These studies also found most of the increase in density takes place in the first day or two. What this tells us is that the early hours and days of a dilbit spill are extremely important, and there is only a short window of time before the oil becomes heavier and may become harder to clean up as it sinks below the water surface.”

      The studies also found conventional means of recovering bitumen was ineffective due to the bitumen sinking into the river sediments. Total cost of clean-up of that spill has reached above $1 billion and the EPA slapped a $177 million fine on Enbridge. I suggest reading the EPA findings on how this spill occurred. World class?

      Liked by 2 people


    What is the viscosity of bitumen if all or most dilutent is removed for shipping? Would it even flow at ambient temperatures of the Salish Sea or Pacific Ocean. Would this increase safety in the event of hull rupture or decrease the chance of a spill during loading off loading. Could the bitumen be handled more like a solid than a liquid?


    • Blair says:

      There is a product called “neatbit” which is simply heated bitumen that can be shipped by train. Have to keep it warm so energy costs are higher. In case of accident it cools and solidifies and thus does not leak. I have not yet heard if any ships have been fitted to ship neatbit


      • Hi Blair. There are no ships fitted for neatbit, unlikely there ever will be. Neatbit by rail is a continental strategy for shipping direct to refineries outfitted to handle bitumen (not all the heavy oil refineries are, sorry I don’t have numbers). Have you read my Alberta Oil Magazine story on neatbit by rail?


      • Blair says:

        I know that, and have read your story. I was simply pointing out the existence of the product not its practicality


  5. Ok, but I bet you didn’t know that I live next door in White Rock… ;0)


  6. Bob Jones says:

    Blair, the Special Report 311: Effect of Diluted Bitumen on Crude Oil Transmission Pipeline 2013
    had very different conclusions to the study of 2016. Probably due to interference from the Obama administration.


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  9. Thanks for this, you have helped focus my opposition and I will try and help others understand where the spills will end up.


  10. jande9 says:

    If the naptha diluent could be converted to automobile gasoline it would help our fuel supply in the lower mainland, reduce our dependence on US refineries, and lower prices for local drivers.
    Is this possible?


    • pwlg says:

      If auto manufacturers around the world have signaled the end of the internal combustion engine why are we so fixated on refining when the 46-52% of the barrel of crude is gasoline? Why would there be a need for so much gasoline in 2030 when most internal combustion engines will no longer be produced?


  11. srveirs says:

    Thank you for helping me understand the underlying (no pun intended) literature. As an oceanographer, I think your analysis would be even more intriguing by digging up some sediment concentrations in Georgia and Haro Strait, particularly within the Fraser River plume, and comparing them with measurements from the Kalamazoo River event and the Douglas Channel DFO study. The oceanography is wonderfully complex in the area through which increased numbers of bitumen-laden tankers would travel (along with heavy commercial and recreational traffic that increases collision risk there).

    Being more quantitative about how dilbit interacts with marine sediments (in all forms) as well as other marine particulates (e.g. plankton) would help us anticipate all likely fates of dilbit should a spill occur. In the few satellite images I’ve seen of the Fraser River plume distribution, it rarely wraps around into Burrard Inlet, which might explain why no OPA formed there in 2007. In a spill within the plume, however, would we expect the bitumen to sink to the pycnocline at the base of the plume (in analogy to the Kalamazoo River) or even deeper?

    What I take home from your piece is that any oil spill (bitumen or crude) within the Salish Sea may may be especially complicated to clean up if it straddles the Fraser plume. The portion of dilbit spill within the Fraser plume may have sunk while the portion outside the plume remains at the surface longer than crude (more time to skim or boom); for crude, the opposite may occur, but likely on a different time scale. In either case, a complete clean-up could require a wider range of equipment and training than a fossil fuel spill in a non-estuarine environment.

    Liked by 1 person

    • pwlg says:

      I’d suggest reading the EPA report on the Kalamazoo River (Marshall, Michigan) system spill. “Of most significance are the physical and chemical changes that diluted bitumen undergoes as a result of weathering. When the diluent component volatizes, the remaining bitumen becomes denser and, depending on circumstances, may aggregate with particles in the water column and remain in suspension or sink to the bottom of a water body. The submergence of persistent residues of diluted bitumen in aquatic environments, as was seen in the Marshall, MI spill, and the potential for long-term deposition in sediments and banks and remobilization in the water column present environmental concerns and cleanup challenges not presented by commonly transported crude oils.” The spill clean-up on the Kalamazoo system began 1 day after the spill on July 27, 2010 and by the Fall of 2014 the EPA signed off and transfered any further clean-up requirements to the Michigan Dept of Environmental Quality. All of the crude spilled has not been recovered but both the EPA and the Michigan State authorities felt any more clean-up would do more harm to the water systems ecology. World Class?

      Liked by 1 person

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  14. Dave Sanders says:

    Excellent article. I am pro-pipeline but wish to understand the position of the opposition. Dilbit is comparable to crude oil, got it. No doubt spills are horrible and tragic. If a spill should occur the clock starts ticking … we must act quickly. After reading this article I understand better the reasons behind a huge federal $1.5 billion investment in spill response. Carbon tax + huge investment in spill response. There’s a method to their madness.


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