The Attached Paper Was Submitted by Environment Canada to the 34Th
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The attached paper was submitted by Environment Canada to the 34th Arctic and Marine Oilspill Program (AMOP) Technical Seminar on Environmental Contamination and Response, held on October 4- 6, 2011, in Calgary, Alberta. The Behaviour of Heavy Oil in Fresh Water Lakes B.P. Hollebone*, B. Fieldhouse, G. Sergey, P. Lambert, Z. Wang, C. Yang, M. Landirault Emergencies Science and Technology Division, Environment Canada Environmental Technology Centre Ottawa, Canada [email protected] Abstract Heavier oils spilled in fresh water have some behavioural similarities to spills in salt water, but their environmental fates strongly reflect the differences between freshwater and marine locations. Some of the environmental factors that can differ in freshwater lakes compared with marine shores include: low water salinity, mixing energies, currents, differing sediment type and size distributions, plant species, benthic types and ecosystems. Many different freshwater spill oil fates have been observed in a recent spill of a heavy residual oil destined for use as an asphalt stock into Wabamun Lake, Alberta. Floating, sinking, submerged, sedimented and refloating oil states have all been reported in the year following the spill. The mechanisms by which the oil reached many of the observed states are unclear and the eventual fate of the oil remaining in the lake remains in question. This paper presents a summary of the analysis of samples gathered over several visits to Wabamun Lake in the first year following the spill. We summarize field reports cataloguing the states of the asphalt stock as the oil aged and the seasons changed. We also present laboratory measurements characterizing samples of oil, water and sediment taken during the site visits over the entire year for oil physical properties; “tarball”/oil particle composition, including sediment, water and hydrocarbon concentrations observed in various oil states. The weathered condition of the oil in the lake is discussed in the context of the physical property and chemical composition data. The sediment and water uptake of the oil in several states has also been measured. Some of the possible mechanisms for the fresh oil evolving into its observed environmental fates are discussed in the context of the field observations and laboratory data. The roles of chemical weathering of the oil, and sediment and water uptake are examined. 1 Introduction On Wednesday, August 3rd, 2005, 43 Canadian National Railway Company (CN) rail cars went off the tracks near the summer village of Whitewood Sands, located approximately 65 km west of Edmonton Alberta, Canada (Alberta Environment, 2005). The lake is in the transition zone between the parkland and boreal forest natural regions and is relatively large (area = 82 km2) and shallow (mean depth = 6.3 m; maximum depth = 11 m). It is generally well mixed, usually with well oxygenated conditions in the entire water column during the open-water period (Mitchell and Prepas, 1990). The lake is moderately- to highly-enriched with nutrients. There is no commercial fishery on the lake, but it is actively fished recreationally for northern pike, yellow perch, and whitefish. The Lake Wabamun basin has a large number of land uses and human activities: coal mining; coal-fired power generation; farming; major road and rail corridors; residential and recreational activities. A mild drought and increased industrial usage have combined to cause gradual decline in lake level since the early 1990s. Lake Wabamun is unique in being one of the most studied aquatic ecosystems in Alberta. Since at least 1942, scientists have been conducting studies on the lake (Schindler et al., 2004). Taken together, these reports provide a great deal of detailed information about the lake ecosystem (Schindler et al., 2004). Of the train cars involved in the derailment, 11 cars containing heavy fuel oil—HFO 7102—ruptured, spilling 712,000 L of warm, highly viscous oil (Golder, 2006). A single car carrying Pole Treating Oil (PTO) also ruptured, spilling an estimated volume of 88,000 L onto the ground at the derailment site (Golder, 2006). The oil was discharged onto the lawns of residences approximately 100 metres north of the lakeshore, on a moderate slope. The heavy fuel oil flowed down the slope, entering the waters of the north shore of Lake Wabamun near Whitewood Sands shortly after the derailment. The oil spilled into the lake through many paths along a broad front of about a 1/2 kilometer. The flow was aided by the fact that the HFO 7102 had been loaded a few hours before and was still warm and relatively less viscous than it would be at ambient temperature. 2 Disposition of the Oil in the Lake following the Spill In the first few days following the spill, the majority of the oil appeared to be floating on the surface of lake. The spilled fuel oil formed a thick, black slick on the lake surface. Silvery sheens (0.05 μm) rapidly covered the lake. By the end of the first day, thin silver sheens of oil covered most of the east end of the lake. Thick (>1 cm) black slicks of oil lined the north shore, east of the spill site (see Figure 2). Tarballs were reported (discrete ‘balls’ of oil from < 1 cm to 10 cm in diameter) submerged in the affected near-shore regions on the first day of the spill (3 August 2005). Within hours, some of the tarballs were showing neutrally-buoyant behaviour, and were seen riding up and down in the water column. Some would rise to the surface, others would be seen sinking to the bottom. No dispersions of oil in water were observed in the lake. Light crude oils are often observed to form a light-brown to red ‘plume’ of oil in water, especially in high wave (surf) conditions. There were no observations during the Wabamun incident. In addition, solid masses of red-brown “chocolate mousse”, a typical form of stable (crude) oil emulsion, have never been reported over the 3 year history of observation at the spill site to date. Systematic field observations were conducted starting on August 11, 2005 using the shoreline clean-up assessment technique (SCAT). The initial SCAT survey indicated the presence of submerged (in the water column, but not touching bottom) and sunken (in contact with the lake bottom) tarballs along the shorelines and in the near shore, shallower areas of the lake. In addition to the smaller tar-ball shapes, sunken oil also formed cylindrical ‘log’-shapes or large patties (> 10 cm diameter, but less than 5 cm thick) of several meters in length and width. During the SCAT survey, the majority of tarballs or patties were observed near the shores, in water depths ranging between 0.1 and 1.5 m with their frequency diminishing with increasing depth. To establish the extent, character and location of submerged and sunken oil, a variety of techniques were employed from the end of August through October, 2005. These included visual surveys along the shoreline (SCAT) and by SCUBA divers in deeper areas, weighted-‘snare’ sampling (weighted oleophilic sorbent), towed bottom trawls (with oleophilic sorbent), and underwater video surveys (black and white, and colour). Observations of presence and character of submerged and sunken oil were collected during the initial SCAT survey, reed bed delineation, shoreline treatment, and post-treatment SCAT survey. In general, observations were made while travelling on foot in water depths ranging from 0.1 to 1.5 m. General observations of the oil conditions include: 1. Submerged and sunken tarballs were frequent in the near shore area adjacent to oiled shorelines and reed beds. After shoreline treatment a high proportion of oil remained. The coverage of oil varied but was highest in treated reed beds (i.e., delineated and cut). Cut reed beds that intercepted wave energy in the near shore areas contained relatively high densities of tarballs. Typically, the tarballs varied in size from 2 to 10 cm. After high winds, the near shore area could have many of these in the area. A sample of one of the larger of these is shown in Figure 5. The tarballs in this area showed a range of densities (specific gravity). Some of them were neutrally buoyant, and moved around in the area, especially when disturbed by water movement. 2. During the initial assessment (August 2005), the tarballs ranged from ‘fresh’ (thick ‘syrup’) to ‘weathered’ (relatively hard with skins of sediment or organic debris). On relatively warm days, some submerged tarballs would float to the lake’s surface and lose their cohesiveness (‘burst’), resulting in an oil slick and associated sheen. See Figure 7. Broken ‘skins’ can be seen in Figures 11 and 12. 3. During post-treatment assessment (October, 2005), the character of the submerged and/or sunken tarballs varied from ‘fresh’ (south- shore) to ‘intermediate’/’tacky’ (north-shore) to highly ‘weathered’ (east-shore). 4. In the reed bed areas tarballs were observed on the bottom, however during the daytime some of these would rise and create a sheen. Often the tarball shed oil from several points around its circumference. An illustration of one of these is shown in Figure 7. A view of tarballs sunk in an oiled reed bed is shown in Figure 8. A ‘deflated’ tarball ‘skin’ is shown in Figure 11. The oil adhered to the reeds also released oil. Tarballs were also seen re-surfacing in areas not in or near reed beds. 5. A ‘slurry’, composed of finely divided organic matter and small oil particles (<1 cm) was observed on the north shore. This is shown in Figure 4. 6. Conglomerations (‘logs’ and large patties) of organic debris and oil observed on the south shore. Most of the organic debris was reed material.