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 0^oC) 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.