Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.
Issue link: http://uscgproceedings.epubxp.com/i/578020
61 Fall 2015 Proceedings www.uscg.mil/proceedings heavier dilbit components are left behind. Weathering and evaporation increases the spilled dilbit density, increasing the risk of sinking and submergence as time progresses. In addition to weathering and evaporation, sedimentation can also increase the probability of sub- mergence, since the sediment in the water is more likely to adhere to the heavier bitumen component. This is not to say that all spilled dilbit will sink. There are many factors that infuence whether dilbit will sink as it weathers, including: • its specifc chemical composition, • the water temperature, • the sediment concentrations in the water body, • the wind, • the current. Indeed, research studies suggest that if environmen- tal conditions are favorable to support foating, dilbit could remain on the surface for up to four days in fresh water and for up to eight days in salt water before sink- ing. 3 Since diluted bitumen may have a higher probability of sinking than other products with similar specifc gravities, this reinforces the need to get personnel and equipment on scene quickly. The faster the response, the greater the chance of recovering the spilled dil- bit from the water's surface using standard response techniques such as booms and skimmers. Addition- ally, a dilbit response requires responders to be aware that, over the course of the response, they might also need to deploy submerged oil detection and recovery equipment. Tools designed to detect and respond to sunken oil include side scan sonar, multi-beam sonar, laser fuo- rescence, visual and video observations, divers, bot- tom sampling, sorbent drops, nets and trawls, dredges, pumps and vacuum systems, remotely operated vehi- cles, and manned submersibles. Responders in the Mar- shall, Michigan, spill were able to locate submerged oil by disturbing the bottom with poles, but a method to determine the exact volume of submerged oil has not yet been identifed. 4 Response Similarities to Conventional Crudes Despite the differences, there are several similarities between diluted bitumen and conventional crudes. For example, both dilbit and conventional crudes follow the same basic weath- ering progression and can be addressed with some of the same basic response technologies and strategies. In the initial (foating) phase of a dilbit spill response, stan- dard equipment such as containment boom, sorbent boom, various skimmers, and vacuum trucks can be used to con- duct the response. Research also suggests that belt, drum, and brush skimmers can be used in the initial stages of the spill and that skimmers designed for more viscous oil would not likely be necessary until several days into the spill. Recent Research and Emerging Technology The recent growth in transport of unconventional products such as diluted bitumen has inspired government, industry, and academia to conduct numerous dilbit-focused research projects. The National Academy of Science is currently working on a study that will analyze whether the dilbit properties difer sufciently from those of commonly transported crude oils to warrant modifcations to spill response plans or cleanup regulations. The study should be available in 2016. The Coast Guard Research and Development Center is also currently engaged in a project to assess the risk of potential dilbit spills as a function of the modes and nodes of trans- port and to identify appropriate response techniques. The Coast Guard Research and Development Center tests a remotely operated vehicle. U.S. Coast Guard photo. These research projects will inform the Coast Guard's understanding of dilbit and help refne response policies and best practices.