1 ABSTRACT
Recent spills of oil sands products (e.g., diluted bitumen (dilbit)) have demonstrated different behavior than that of conventional crude oil. Spill responders have the challenge of developing effective response strategies for dilbit spills in the freshwater environment because they are unable to ascertain when floating products might sink, especially when naturally occurring sediments are present.
The U.S. Coast Guard Research and Development Center (USCG RDC) executed oil-weathering experiments to assess the physical and chemical properties of two common dilbit products, Cold Lake Blend (CLB) and Western Canadian Select (WCS) in fresh water at three sediment concentrations: 0 mg/L, 100 mg/L and 1000 mg/L in both winter, fall (i.e., cold weather and limited solar exposure) and summer environmental conditions (i.e., warm weather and high solar exposure). The experiments took place between November 2021 and December 2022 at the U.S. Army Corps of Engineers’ Cold Regions Research and Engineering laboratory (CRREL) in Hanover, New Hampshire.
The experiments included dilbit sampling for 30 days and measured dilbit product components for chemical analysis to track evaporation and degradation. Analysis of Variance tests were conducted to evaluate the impact of sediment concentration using the loss of total petroleum hydrocarbons (TPH). At day 15, CLB in water with zero sediment had a higher TPH loss by comparison to CLB in water with a high sediment concentration. It is likely that the binding of the CLB to sediment and subsequent settling reduced oil loss. There was no statistical difference for the WCS.
Visual observations revealed that the dilbit physical appearance changed drastically by day 8 and combined with chemical-analysis data. suggests that the window of opportunity for floating product removal could be a few days. The results from these experiments will eventually provide USCG Federal On Scene Coordinators (FOSCs) with a practical guide for responding to these spills, potentially minimizing adverse impacts on endangered species and other wildlife, plants, and potable water supplies. Future research should include more spatial and temporal measurement frequency, and containment and recovery methods used to clean up dilbit after sinking.