Spill Response Planning
The identification of an oil spill triggers the mobilization of personnel and equipment to protect the health and safety of the public, and to detect, contain, and recover the spilled oil while minimizing impacts to communities and the environment. Many characterizations of risk include probabilistic considerations of the magnitude and frequency of the hazard itself; for example, in the case of hurricane storm surge, these factors are estimated based on historic data. The multiple factors that can contribute to spill occurrence can include unpredictable accidents resulting from human actions; for example, the 2007 diluted bitumen spill in Burnaby, British Columbia (Box 3-4), was the result of construction activities unrelated to pipeline operations.37b The vulnerability of communities and environments potentially affected can be assessed in advance, however, and these factors become a key component of spill response planning.
For crude oil spills from transmission pipelines, the corridor of potential release is at least fixed and the impact areas are predictable. The types of environments, communities, and facilities that could potentially be impacted, and their sensitivities and vulnerabilities, can thus be identified in advance and are essential elements of spill response planning. Where the characteristics of the right of way are such that it is more or less sensitive to spills of different materials (e.g., diluted bitumen versus medium or light crude oil), these factors can be considered in advance; however, the specific characteristics of the material may change over time in any transmission pipeline operations, particularly for pipelines transporting diluted bitumen.
The transport, fate, and effects of spilled oil depend not only on the characteristics of the oil but also on the environments and conditions at the time and place of the spill. The consequences of a spill of diluted bitumen into a stream at base flow will differ from those at flood conditions based on the effect of turbulence on suspended particle formation, the availability of sediment particles for adhesion, the extent of the riparian or floodplain zone at risk, and the length of stream affected within the first few days. Similarly, the public safety issues surrounding volatilization of lighter fractions would be different in a recreational community on a holiday weekend compared to midweek during low season. Every spill presents a unique combination of conditions. Responders on scene must use their experience to adjust the response plan to the circumstances that confront them.
Given this uncertainty regarding the magnitude and character of any specific incident, spill response planning for pipelines is based on the concept of the “Worst Case Discharge,” which is the largest foreseeable discharge of oil, including a discharge from fire or explosion, in adverse weather conditions. This is calculated as follows:113
The Worst Case Discharge is the largest volume, in barrels (cubic meters), of the following:
- The pipeline’s maximum release time in hours, plus the maximum shutdown response time in hours (based on historic discharge data or, in the absence of such historic data, the operator’s best estimate), multiplied by the maximum flow rate expressed in barrels per hour (based on the maximum daily capacity of the pipeline), plus the largest line drainage volume after shutdown of the line section(s) in the response zone expressed in barrels (or cubic meters); or
- The largest foreseeable discharge for the line section(s) within a response zone, expressed in barrels (or cubic meters), based on the maximum historic discharge, if one exists, adjusted for any subsequent corrective or preventive action taken; or
- If the response zone contains one or more breakout tanks, the capacity of the single largest tank or battery of tanks within a single secondary containment system, adjusted for the capacity or size of the secondary containment system, expressed in barrels (or cubic meters).
In addition, pipeline operators may claim prevention credits for breakout tank secondary containment and other specific spill prevention measures.
This chapter outlines the main elements of spill response planning relevant to the consideration of diluted bitumen, describing the types of plans developed under the National Contingency Plan (NCP) and considering potential protection priorities for diluted bitumen spills. The roles and responsibilities of various agencies and entities in the development of these plans, including the NCP process, are described in Chapter 6. The next section focuses on activities that occur during actual spills and how these may need to vary for spills of diluted bitumen compared to crude oils. The chapter concludes with a summary of the specific challenges for spill response planning and implementation presented by the transport of diluted bitumen in pipelines.
Predicting the Behavior of Spilled Oil
In framing and scaling an actual incident, responders ask the following questions:
- What and how much was/is being spilled?
- Where will it go?
- What are the resources at risk?
- What are the likely impacts?
- What should be done to reduce these impacts?
The observed type and volume of the spilled product drives initial actions related to the safety of responders and the public, mobilization of equipment, and estimates of the crude oil’s likely behavior and pathway in the environment. Any delay in access to accurate information about the composition and properties of the spilled product can significantly affect the effectiveness of the response. Access to such information is critical, but specific compositions of products being transported by pipelines are usually not promptly available from pipeline operators or from the sources of the products they transport, and often vary over time in a particular pipeline. Compositional information is particularly important for diluted bitumen because the types and concentrations of diluents vary in ways that strongly affect the behavior of the spill and thus response strategies. Safety Data Sheets (SDSs) for crude oils are usually generic and provide ranges in reported properties, such as density; they do not provide information that responders need, such as the specific type of crude oil, density after weathering over time, chemical composition, and adhesion (which is rarely provided), among others. Because of their generic nature,
responders seldom obtain the data they need from an SDS. If the crude oil name is provided and the crude oil is a standard type, readily available databases, such as Crudemonitor.ca, the Environment Canada oil properties database, and the National Oceanic and Atmospheric Administration (NOAA) Automated Data Inquiry for Oil Spills (ADIOS) oil library, can be consulted to obtain some of these data. However, if the spilled material is a blend that does not have a standard composition, but rather may change significantly from batch to batch, these databases may provide incomplete or inaccurate information. In such cases, batch-specific information is needed.
Modeling for guiding response activities is typically done for short durations and, thus, differs from modeling conducted to evaluate long-term impact. NOAA ADIOS is designed to provide oil weathering information for only 5 days. In addition, the NOAA Environmental Response Division uses the General NOAA Operational Modeling Environment (GNOME) to obtain modeling results of oil transport on the water surface, and the main purpose of these results is assisting the Unified Command of a spill in making the appropriate response decision. Such models would need to run with a minimal number of parameters and to attempt to capture the salient features of the release in terms of direction and magnitude.
While existing oil spill models can be used for the response to diluted bitumen spills, the main parameters are typically calibrated to conventional oils. For example, the windage factor, which provides the transport speed of oil, is typically equal to 3% to 4% in the early stages of a conventional oil spill,87 and it is later decreased further as the oil weathers and forms emulsions. For diluted bitumen, the residual oil density can increase rapidly with the evaporation of the volatile diluent components. Since diluted bitumen does not promote the formation of emulsions, the windage factor of a diluted bitumen is initially low (e.g., 3%) and is not expected to decrease further with time. Another challenge in using existing oil spill models for diluted bitumen is the lack of sufficient experimentally obtained data to calibrate the modules with diluted bitumen.
Because volatile organic compounds (VOCs) can evaporate rapidly when crude oil is released to the environment, public and worker safety related to air quality must be considered during the early stages of the response.88 Light crude oils, particularly those produced during hydraulic fracturing of shales (e.g., Bakken and Eagle Ford) can pose significant air quality and explosion risks early in the response. Because benzene is a known carcinogen that is present in many petroleum products, it has the
highest ranking in terms of potential for exceeding occupational exposure levels and community-exposure guidelines.89 However, there may also be concerns about and monitoring of other VOCs, hydrogen sulfide, and explosion hazards (Chapter 3).
When air quality is a particular concern, there may be the need to establish a Public Health Unit within the Planning Section of the Unified Command to develop criteria for evacuations and reoccupation by the public. In addition, the Site Safety Plan for responders will have to follow Occupational Safety and Health Administration (OSHA) and American Conference of Industrial Hygienists guidelines for VOCs in general, and benzene, toluene, ethyl benzene, and xylenes in particular, as well as for hydrogen sulfide and other contaminants of concern. There may also be a need for real-time measurements of concentrations in work areas and for use by workers of passive air-monitoring and dosimeter badges, which are sent for analysis in order to monitor exposure. A program of this kind was implemented during the recent spills of diluted bitumen in Marshall, MI (Box 3-1),12 and Mayflower, AR (Box 3-5), where the oil spread to areas in close proximity to residential areas.
Effects on water quality can also be significant. Spills of crude oil that reach water bodies can result in either closure of the affected water body to public use or posting of advisories to avoid oiled areas until there is no longer a potential for exposure. Such closures and advisories are likely to be longer when the spilled oil sinks in the water body and generates chronic sheening. For example, the Kalamazoo River and a reservoir known as Morrow Lake were closed for nearly 2 years after the Enbridge Pipeline spill in July 2010 (Box 3-1). Drinking water intakes may be shut down until testing determines that the water is safe to use, or the raw water may require additional treatment such as aeration and carbon filtration, as was conducted during the 2015 spill of crude oil from the Bridger Pipeline in Glendive, Montana, into the ice-covered Yellowstone River.90
Cleanup endpoints are the criteria against which the response actions are measured, to determine if the goals and objectives have been met. Cleanup endpoints generally are set for water, shorelines, and soils. For spills in coastal and marine habitats, cleanup endpoints are usually based on the following guidelines91 rather than analysis of samples for measurement of the concentration of selected contaminants:
- No oil observed: not detectable by sight, smell, or feel;
- Visible oil but no more than background amounts of oil;
- No longer generates sheens that will affect sensitive areas, wildlife, or human health;
- No longer rubs off on contact; and
- Oil removal to allow recovery/recolonization without causing more harm than natural removal of oil residues.
Cleanup endpoints for a specific spill are developed through consensus among the stakeholders, which can include public health officials. Key considerations are the trade-offs between aggressive techniques that remove the oil but also cause additional damage versus less intrusive techniques that rely on natural processes to remove, dilute, or bury residual oil (collectively known as natural attenuation). Cleanup endpoints for inland oil spills tend to be more stringent than those applied to spills in the marine environment and often require the use of more intensive cleanup methods that carry a risk of increased ecological impacts92 for the following reasons:91
- Inland habitats often lack some of the physical processes (such as waves and tidal currents) that can speed the rate of natural removal of oil residues after treatment operations are terminated and can affect smaller water bodies where there are slower rates of dilution and degradation.
- The direct human uses of inland habitats, such as for drinking water, recreation, industrial use, and irrigation, require a higher degree of treatment compared to marine environments to avoid human health and socioeconomic impacts.
- Spills in close proximity to where people live, work, or recreate often require treatment to a higher level.
- There may be large-scale differences in water levels during the response, causing oil to be stranded well above normal levels where it can pose hazards to wildlife as well as humans using these areas.
- Many states have sediment quality guidelines that must be met as part of the remediation phase after the emergency response is completed.
Table 4-1, which has been adapted from Whelan et al.,92 lists guidelines for establishing cleanup endpoints for spills in inland habitats. Achieving consensus on cleanup endpoints for spills of diluted bitumen can be challenging if the crude oil sinks and continues to generate sheens in areas of high public use, or where the residual crude oil adhering to substrates is difficult to remove.
TABLE 4-1 Guidelines for Selecting Cleanup Methods and Endpoints for Different Inland Habitats
|Basis for Treatment||Applicable Habitats||Treatment Methods||Example Primarya Cleanup Endpoints||Guidelines for No Further Treatment Determination|
|Protection of Public Health and Safety||
|Protection of Sensitive Resources and Habitats||Wetlands, bird nesting areas, T&E species habitat, wildlife refuges, national parks, other protected areas||
|Removing Aesthetic Impacts in High-Use Areas||
|Basis for Treatment||Applicable Habitats||Treatment Methods||Example Primarya Cleanup Endpoints||Guidelines for No Further Treatment Determination|
|Removing Contact Hazard (both humans and wildlife)||
|Mitigating Persistent Sheens||
In low-use areas:
|Mitigating Intermittent Sheens (triggered by rainfall, temperature changes, etc.)||
In low-use areas:
|Mitigating Sediment/Soil Contamination||
aSecondary Cleanup Endpoints should include “Or, as low as reasonably practicable considering net environmental benefit.”
SOURCE: Adapted from Whelan et al.92
TACTICS FOR DETECTION, CONTAINMENT, AND
RECOVERY OF SPILLS OF DILUTED BITUMEN
Spills on dry land, if detected early, are often readily contained and recovered before extensive contamination of soil or groundwater (Chapter 3). One recent study93 found that diluted bitumen penetrated a sand column more slowly than light, medium, and heavy conventional crude oils, indicating diluted bitumen soaked into sandy substrates may be no more difficult to recover than other crude oils. Problems occur when a light crude oil is released underground and not detected for days to months, or when the release is into a highly permeable substrate. When a pipeline released light crude oil underground in a gravel-outwash plain near Bemidji, Minnesota (Box 3-2), the combination of both of these factors led to one of the most extensive (and studied) incidents of groundwater contamination.68 A more recent example is the subsurface release of about 20,000 barrels of Bakken crude oil from a pipeline in agricultural land near Tioga, ND. The light crude oil penetrated more than 30 ft into the ground. Extensive excavation and treatment of soil is required and is expected to take 2 years to complete.
Recovery methods for spills on land include manual and mechanical removal followed by offsite disposal, burning of oil that is pooled on the surface or in depressions and ditches, high-temperature thermal desorption or incineration (followed by return of treated soils to the spill site once they meet endpoints), and bioremediation of residual oils after gross oil removal. Cleanup of land spills is usually completed in weeks to months. When groundwaters are contaminated, cleanup is far more challenging and can extend over decades of time, with associated high costs.
Floating crude oil is detected mostly by aerial observations, ground and water surveys, and, depending on the spill size and characteristics, remote sensing. These methods are well established and effective for any floating crude oil. These methods fail, however, when the crude oil submerges or sinks. Methods of detection employed in such cases have included (i) sonar systems, (ii) underwater cameras and videos, (iii) diver observations, (iv) sorbents, (v) laser fluorosensors, (vi) visual observations from the water surface, (vii) bottom sampling, (viii) water-column sampling, and (ix) the combination of in situ mass spectrometry with autonomous underwater vehicles.94 These methods are not well estab-
lished, are relatively slow, often provide only a snapshot of a small area, and suffer from many limitations depending on conditions such as wave height, water depth and currents, water turbidity, and ability to detect buried crude oil. Disturbance of sediments with a disk on a pole, followed by observations of floating crude oil globules and sheen appearing at the surface, was the preferred method for field detection and mapping of submerged oil in the case of the diluted bitumen spill into the Kalamazoo River near Marshall, MI.
On Water Containment and Recovery
Because most crude oils that could be released from pipelines are expected to float initially, the first response actions are to deploy booms to contain the crude oil and protect sensitive areas, and use of skimming, vacuum, and sorbents to recover the contained crude oil. When booms are deployed quickly and well, a large amount of the floating crude oil can be recovered, particularly in streams and rivers where the crude oil is contained between the banks. However, there are many conditions where floating crude oil cannot be effectively contained and recovered, including high-flow and turbulent conditions in rivers; strong winds and large waves, especially in estuaries and coastal waters; coverage of a water body by snow and ice; and limited access, such as in remote areas, floodplains, other wetlands, and difficult terrain. Under these conditions, responders look for downstream or downcurrent locations where response equipment can be effectively deployed. On rivers, these can include impoundments, bridge crossings, and boat ramps. Temporary roads may have to be constructed to gain access, particularly to wetlands and small streams.
As diluted bitumen weathers and the diluent is lost by volatilization, the floating bitumen will become highly viscous and require specialized skimming and pumping systems capable of handling such high-viscosity oils. Mesocosm tests with Cold Lake Winter Blend (CLWB) with an initial thickness of 30 mm floating on water in outdoor tanks, where the oil increased in viscosity over time up to 30,000 cP, showed that conventional heavy oil skimmers were effective.9c However, under real-world conditions, depending on the source and temperature, weathered diluted bitumen can increase in viscosity up to 1,000,000 cP (see Chapter 2).94 Moreover, the residue may not continue to float (Chapter 3), a possibility not addressed by most spill response plans that exist today.
Weathered diluted bitumen adheres strongly to shorelines, vegetation, and debris and will be more difficult to remove from these surfaces
for on water recovery by flushing methods, compared to conventional crude oils. The adhered oil will also pose a threat of fouling of habitats and wildlife because it will more quickly weather into a viscous, sticky residue.
The efficacy of dispersants is related to the viscosity of the spilled crude oil. Based on laboratory95 and mesocosm studies9c with the diluted bitumens CLWB and Access Western Blend (AWB), interactions with dispersants exhibit roughly the same dependence on viscosity. Accordingly, dispersants are moderately effective at 10,000 cP but have little to no effectiveness at viscosities >20,000 cP. Diluted bitumen, for which the viscosity thresholds are reached within 6-12 hours under mild to moderate open water conditions and at temperatures of 15°C to 20°C, therefore have a narrower window of opportunity for effective use of dispersants than conventional crude oils. In comparison, medium crude oils are expected to reach these thresholds within 24-72 hours in temperate conditions and possibly within 12-24 hours during the winter.46a
Mesoscale tests9c showed that burning is viable on diluted bitumen weathered up to 1 day, with removal efficiencies of 50% to 75%. The burn residues were sticky and easily submerged; thus, there would need to be rapid removal of the residues to prevent sinking. In comparison, medium and heavy crude oils are expected to burn at 85% to 99% removal efficiencies over longer periods of weathering, thus generating much lower amounts of burn residue. Formations of stable oil emulsions containing >25% water are difficult to ignite and burn less efficiently,96 regardless of the oil type. However, the mesocosm studies showed that the water uptake in both AWB and CLWB was as a mechanically mixed and unstable oil-water combination, and not as a stable, uniform emulsion (see discussion of emulsification in Chapter 3). Such combinations would likely break up during calm-water periods, which might increase the effectiveness of a burn.
Because diluted bitumen spills are expected to adhere strongly to surfaces, tests have been conducted using chemical agents designed to enhance crude oil removal and listed on the National Product Schedule under the heading of Surface Washing Agents. Studies have shown that
CLWB that had weathered on granite tiles under various conditions (on water, in sun, or in shade) could not be removed by low-pressure, ambient-temperature water, but could be removed by high-pressure, high-temperature flushing when used in combination with a surface washing agent after up to 5 days of weathering.9c Similar results were obtained during the response to the Burnaby spill (Box 3-4).76 As in all spills, early application of surface washing agents increases their effectiveness. In fact, their use has been preapproved by Regional Response Team 6 since 2003.97 During the Refugio spill, responders reported success in removing weathered oil from surfaces using dry-ice blasting, a technique that may also find application with surface cleaning of diluted bitumen (Box 3-3).
RESPONSE TO NONFLOATING CRUDE OIL AND ITS RESIDUES
When crude oil is suspended in the water column or sinks to the bottom, response tactics must change. There are no known, effective strategies for recovery of crude oil that is suspended in the water column, particularly where it occurs as droplets or oil-particle aggregates. Accordingly, the objectives are to track the suspended material and to predict where it may sink to the bottom. Nets with various mesh sizes and towed at varying speeds have been tested to determine the adhesion and leak rates for diluted bitumen and its residues.98 Submerged material adhered to nets that extended to 0.5 m depth with minimal leakage at tow speeds of 0.3 m/s (0.6 knots) for fine and medium mesh sizes. When full, the nets weighed 25 kg/m2, making them difficult to recover by hand, and 25% to 50% of the oil leaked out when the nets were removed from the water. The recovered material stuck so firmly that the nets could not be reused. Submerged material deeper in the water column was swept under the net at water flow rates of 0.3 m/s.99 Similar results have been reported for heavy oils, indicating that the use of nets as a removal method for any type of oil suspended in the water will be of very limited effectiveness. Ideal conditions would be in low-flow, relatively small rivers or streams where the nets could be placed across the water body and readily replaced before they failed. In open water environments, submerged oil would first have to be located and the nets then deployed quickly and effectively, which seems unlikely.
Other tactics for removal of oil suspended in the water column include various types of filter fences, such as gabions (wire cages) stuffed with sorbents (usually “Oil Snare,” a polypropylene adsorbent) placed on the bottom downstream from the release or snares attached to frames placed downstream. None of these tactics has been documented as effective.
Tactics for removal of sunken crude oil include suction dredge, diver directed pumping and vacuuming, mechanical removal, manual removal,
sorbents, trawls and nets, and agitation/refloating. Suction dredging is a standard technique for removing sediments from the bottom of a water body, and it has been used to recover sunken crude oil during at least five spills and most extensively after the Enbridge pipeline spill in the Kalamazoo River (Box 3-1). This method generates large volumes of water and sediment that have to be treated and properly disposed of. Thus, it works best for surgical removal of small concentrated areas of sunken crude oil.
The method used most frequently for removal of bulk crude oil that has accumulated at the bottom of a water body is diver directed pumping and vacuuming. Divers can target the sunken oil and regulate the flow to minimize removal of ancillary water and sediment. The rate of pumping must be adjusted to prevent shearing and emulsification of the oil, and to effectively move highly viscous oils.
When the sunken crude oil is solid or semisolid, removal using an excavator, clamshell dredge, or other mechanical equipment can be effective and, under favorable conditions, generates little additional water or sediment for handling and disposal. This equipment is readily available and, if deposits are near shore, can be operated from land. Deployment from barges is also feasible, but there are depth restrictions (< 6 m), the equipment is large and heavy, and the rate of recovery is slow.
Where the sunken oil occurs in discrete patches, manual removal in shallow water by wading, or in deeper water by divers, can be effective and allow selective recovery of crude oil if visibility is adequate. However, it is labor intensive and slow, and requires specialized gear for diving in contaminated water and special procedures and supplies for decontamination of divers.
Where the sunken material consists of oil-particle aggregates, it may be possible to refloat the crude oil by agitation of the bottom. Agitation using rakes or similar tools, injection of water using water wands, and injection of air using equipment such as pond aerators were all used during the cleanup of the Enbridge pipeline spill in the Kalamazoo River (Box 3-1).9a The refloated crude oil was recovered using skimmers or sorbents. However, depending on the conditions, a significant amount of the crude oil or oiled sediment sinks back to the bottom. The agitation can also simply mix the crude oil more deeply into the sediment. Careful testing is needed to determine the effectiveness of these methods.
Sometimes, crude oil from sunken aggregates returns to the surface as the water warms and the oil becomes less viscous and is able to separate from the sediment; it is not likely that the increased temperature affects the oil density relative to the water density.100 Gas bubbles released naturally from the sediment can also result in oil transport to the surface, through a process known as ebullition.101
Management and minimization of wastes are key challenges during response to a spill. Any activities that increase the volume of oily waste will have a large impact on cost. For spills where the crude oil initially floats, then sinks, the response team will be faced with the management and disposal of conventional waste materials, such as sorbents, protective gear, skimmed oil, oiled solids removed from land, oiled debris, and oily liquids, as well as any materials collected during detection and recovery of sunken crude oil. If the recovery of sunken crude oil involves methods such as pumping, vacuuming, or dredging, very large volumes of crude oil, water, and sediment will be generated, requiring separation into different waste streams for further treatment prior to disposal. For example, over 237,000 yd3 of materials were removed from the Kalamazoo River and its floodplain in 2010-2014 after the Enbridge pipeline spill.102
Because the collected crude oil may either float or sink and the character of the waste stream will vary widely over time, decanting systems tend to be custom designed. Waste management is typically divided into three phases: (i) separation and treatment of solids, (ii) separation and treatment of liquids, and, where allowed, (iii) final polishing of liquids prior to release at the spill site. Where wastes can be treated on land, methods such as dewatering using geotubes (requiring a large footprint for the treatment area) and carbon treatment of water are used. Geotubes are sediment-filled sleeves of geotextile fabric. Where wastes can or must be treated at the site, a series of decanting tanks (onshore) or barges (on the water) is used, often with the goal of being able to discharge the treated water back into the spill site. Table 4-2 provides a summary of the effectiveness of selected response tactics for spills of conventional crude oils compared to spills of diluted bitumen.
Spills of diluted bitumen will initially float regardless of the water density; thus, the first response actions are similar to those employed after spills of conventional crude oil. However, as the diluted bitumen weathers, its properties change (see Chapters 2 and 3) in ways that can affect the response. The time windows during which dispersants or in situ burning can be used effectively are much shorter for spills of diluted bitumen than for spills of conventional crude oils. The strong adhesion of diluted bitumen to surfaces requires higher pressures and temperatures when using flushing techniques. Because it is already highly degraded, natural attenuation of residual diluted bitumen is less likely to be effective, which can trigger the need for more aggressive removal actions.
TABLE 4-2 Effectiveness of Selected Response Tactics for Conventional Crude Oils Compared to Diluted Bitumen in Seawater
|Tactic||Light Crude||Medium Crude||Heavy Crude||Diluted Bitumen|
|Dispersant Effectiveness||50% to 90% up to 72 hr||10% to 75% up to 72 hr||0%a||~50% at 6 hr ~0% after 12 hr|
|In Situ Burning||99% at 96 hr||99% at 96 hr||90% at 96 hr||50% to 75% up to 24 hr; not effective after 96 hr|
|Removal of Oil Adhered to Substrates||Washing with low pressure, ambient temperature||Washing with higher pressure, and higher temperatures||Washing with high-pressure, hot water; may require use of surface washing agents; dry-ice blasting||Washing with high-pressure, hot water; may require use of surface washing agents; possibly dry-ice blasting|
|Waste Generation||Lowest because of high natural removal processes||Moderate||High||Potentially highest, if benthic sediment removal is required|
aBased on review of laboratory dispersant effectiveness tests reported by Environment Canada in the online Oil Properties Database.
SOURCE: Environment Canada31
Most spill response tactics are based on the assumption that the crude oil will float. When a significant fraction of the spilled crude oil becomes suspended in the water column or sinks to the bottom, the response becomes more complex because there are few proven techniques in the responder “tool box” for detection, containment, and recovery. Recovery of sunken crude oil often generates large amounts of water and sediments that require complex logistics for handling, separation, treatment, and proper disposal of wastes. When sunken crude oil refloats spontaneously over a protected period, it can trigger the need for aggressive removal to mitigate the threats to water intakes, the public, fish, and wildlife. All of these threats are greater for spills of diluted bitumen than for spills of commonly transported crude oils. They drive the need for more complete removal of spills in inland areas where cleanup endpoints are usually more stringent.
Every spill presents a unique combination of materials and conditions. Better documentation of the behavior of diluted bitumen when spilled and of effective recovery methods is needed, so that the response community can benefit from these experiences.