Diluted bitumen is a form of crude oil derived from bitumen that is extracted from tar sand deposits. It has unique properties that deserve special attention to limit the ecological impact in the event of an oil spill. According to a report recently released by the National Academies of Sciences, Engineering and Medicine, if the US Department of Transportation (DOT) wishes to improve preparedness for accidental diluted bitumen spills, it has to change its regulations and planning procedures, taking these unique properties into consideration.

“The recommendations set forth in our report represent a practical and pragmatic approach to mitigating the unique concerns associated with spills of diluted bitumen,” said committee chair Diane McKnight, professor of civil, environmental, and architectural engineering and a fellow of the Institute of Arctic and Alpine Research at the University of Colorado.

Bitumen is a dense and heavy crude oil extracted from Canadian tar sands. It is diluted with lighter, less dense oils before being transported across the Canadian border into the United States via pipelines. While diluted bitumen has been piped into the US for over 40 years, due to improvements in extraction technologies together with an increase in the rate of production, and consequently an increase in the volumes being exported by Canada, existing pipelines are being expanded and developed further, with new pipelines being proposed to cope with the increase in the rate of production.

While a 2013 study showed that diluted bitumen does not pose a greater risk of accidental spillage than other forms of crude oil being transported via pipelines, DOT requested a follow-up study to determine whether, in the event of a spill, diluted bitumen possessed any unique properties that warranted changes to preparedness and/or cleanup regulations, or changes to oil spill response planning.

According to the newly released report, such changes are indeed warranted. While diluted bitumen tends to behave much like any other crude oil immediately after a spill, environmental exposure rapidly triggers unique chemical and physical changes, or ‘weathering’, that do not occur in other types of crude oil. Within just a few days, diluted bitumen undergoes a transformation, changing from a light, fluid oil into a heavy, viscous residue, laden with sediment that is difficult to recover using conventional oil spill

response techniques. The tacky residue tends to stick to surfaces, making it difficult to cleanup, and because it is heavy, is particularly problematic when spilled into waterbodies, as it can become submerged or even sink to the floor where it is difficult to recover from benthic sediments.

Compared to other types of crude oil that are commonly transported along pipelines, the manner in which diluted bitumen transforms after weathering warrants greater concern and calls for a more focused approach in terms of response strategies and mitigation tactics, says the report. However, current regulations and best practices recommended by DOT’s Pipeline and Hazardous Materials Safety Administration (PHMSA) don’t consider the unique characteristics of diluted bitumen; they also fail to outline an effective mitigation plan that specifically address the unique problems associated with diluted bitumen spills. A comprehensive and more focused approach is required to ensure we are adequately prepared for a diluted bitumen spill, and to ensure swift and efficient cleanup and effective mitigation in the event of such a spill.

The report suggests that the PHMSA modifies the Part 194 regulations to ensure better planning that effectively anticipates a diluted bitumen spill so that an appropriate response strategy can be implemented should a spill of this nature occur. The report makes several recommendations to this effect, including the following:

• PHMSA should ensure that response plans outline procedures which pipeline operators will follow in the event of a spill to notify a designated official of the name and source of any spilled diluted bitumen within 6 hours of a spill; and if so requested, to supply an oil sample of the spilled diluted bitumen together with details of the composition of the mixture within a 24 hour window period.
• The PHMSA should ensure that response plans provide a detailed description of resources and activities that will be implemented to mitigate the impacts of diluted bitumen spills, including outlining the capabilities for detection, containment and recovery of submerged oil and/or sunken oil resting on benthic sediments.
• The PHMSA should collaborate with the US Environmental Protection Agency (EPA) and the US Coast Guard (USCG) to ascertain whether response plans are adequate for mitigating diluted bitumen spills.

The report also suggests that further research in needed in several areas to improve overall response to diluted bitumen spills, including: 1) improving methods to isolate and recover submerged diluted bitumen from moving water; 2) finding alternative methods to dredging to recover diluted bitumen that has settled on bottom sediments; 3) understanding the environmental and human health risks associated with weathered diluted bitumen.

Reference

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