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Oil in the Sea IV: Inputs, Fates, and Effects (2022)

Chapter: 4 Accidental Spill Mitigation

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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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4

Accidental Spill Mitigation

Oil inputs from accidental spills can be substantially reduced through prevention and source control. It is important to have tools available to effectively respond and minimize volume of oil spilled and the impact on people and on the environment should there be a need. This chapter discusses operational consideration of the various options available to respond to accidental oil spills and the rationale for the selection of response techniques, the pros and cons of each measure, a realistic assessment of their effectiveness under various conditions, and suggestions for future improvements.

4.1 SOURCE CONTROL

4.1.1 Salvage as Source Control for Vessel Spills

When a vessel is involved in a major accident—a collision, allision, or grounding—there is a risk of oil being released into the environment. Although double hulls on cargo and bunker tanks add a level of protection that reduces the likelihood and potential volume of a release in an impact accident (also see Section 3.2.4.1) (Rawson et al., 1998; Michel and Winslow, 2000; NRC, 2001; Herbert Engineering Corp. and Designers & Planners Inc., 2003; Barone et al., 2007; Yip et al., 2011b), there is still a chance of an oil release. Furthermore, as discussed in Chapter 3, as the capacity of both tankers and cargo ships increases, the vessels potentially become less maneuverable and the impact force, should a collision occur, potentially increases.

In the event of a vessel accident in which there is a risk of an oil release, the vessel operators exercise their vessel response plan (VRP) and alert not only the appropriate coast guard authorities, but also the salvage and marine firefighting (SMFF) organization named on their plan or recommended by authorities. The SMFF providers are equipped and trained to

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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extinguish fires and to secure stability and structural strength of the vessel to prevent further damage to the vessel and to prevent or reduce oil outflow from the cargo and bunker tanks. Much of this work is accomplished with large cranes and machinery, as well as with trained divers. In some cases, the source control work of salvage teams involves lightering the vessel—or removing the oil into another vessel or storage tank. Preventing releases or at least reducing the amount of oil released, in the event of a vessel accident is the first level of mitigation in preventing the effects of large oil spills.

Ensuring that VRPs and SMFF response capabilities are appropriate to meet the needs of existing and future vessel traffic will be an important mitigating factor for large tanker and non-tank vessel spills (GAO, 2020).

4.1.2 Offshore Wells

In the pursuit of readiness to respond to a potential oil spill from an offshore exploration and production (E&P) facility, the primary approach of both the regulatory community and the industry community is prevention of and preparedness for incidents. Great advances have been made in recent years in blowout prevention and source control. Prevention can be achieved through adherence to drilling standards and safety regulations combined with a culture of safety and proactive risk management (see Section 3.5.1 for more details). During drilling operations, well parameters are continuously monitored and warning systems exist to alert operators of a potential threat to well integrity. This real-time well monitoring information is often displayed simultaneously in several locations, and examined by different teams of experts to ensure that any deviation from normal operations is immediately detected and mitigated. Among other parameters, these systems can monitor the condition of well barriers. A barrier is defined as a system or a device that can be used to contain fluid or pressure within the well. These barriers may include high-pressure wellhead housings, multiple casing strings cemented in place, blowout preventers, and weighted drilling fluids. Drilling standards require at least two independent barriers to be maintained at any given time (API, 2018b,c; IOGP and IPIECA, 2019) to prevent a single failure from leading to a loss of well control and a resulting spill. Barriers are tested prior to and after installation, as well as at regular intervals during operations. Should the prevention systems fail, resulting in an uncontrolled release of oil to the environment, a variety of well intervention activities are designed to take place.

The primary well control barrier is the weighted drilling fluid that maintains hydrostatic pressure in the wellbore at a higher level than the pressure in the reservoir, thus preventing hydrocarbons from entering the wellbore. Its composition and density are designed for specific well conditions and are continuously monitored throughout drilling operations. A blowout preventer (BOP) is a device installed subsea on a wellhead or at the rig and is specifically designed to prevent uncontrolled release of gas and fluids from the well (API, 2018b). It serves as a secondary well control barrier. The BOP consists of a series of devices to close off the wellbore in various conditions, including cutting jaws (called “shear rams”) to slice through the pipe and seal off the well in case of an emergency. A BOP must be able to cut the drill pipe and seal the well under the maximum anticipated pressure. In the United States, the Bureau of Safety and Environmental Enforcement (BSEE) requires a BOP to be certified and tested to ensure readiness of all components. If an early warning system indicates a potential loss of well containment, the BOP can be activated to seal the well before oil escapes, either remotely or using a remotely operated underwater vehicle with the help of a subsea intervention skid.

In the event that the primary and secondary well control measures fail, additional source control activities can be initiated (API, 2006). A new well can be drilled to intersect and kill the well experiencing loss of containment. Relief well operations are effective but may take time, during which escaping oil may negatively affect the environment. This issue was addressed by the development of the subsea capping stack and containment equipment technologies. Subsea capping involves installing a capping stack (see Figure 3.7) onto the well and then closing its valves to shut off the flow of hydrocarbons and seal the well. Capping stacks should be capable of withstanding the maximum anticipated pressure at the wellhead. Some of them weigh almost 400,000 pounds and operate in temperatures as high as 400°F, pressures of 20,000 psi, and water depths up to 15,000 ft water depths (IOGP and IPIECA, 2019). The main advantage of the capping stack is its ability to isolate and stop the flow in a relatively short period of time. A Global Subsea Response Network (GSRN) was formed to leverage collective expertise of leading source control companies and ensure that best equipment and practices in source control are available worldwide.

If it is not possible to safely shut in a well with a capping stack, containment methods can be used to prevent the environmental impacts while a relief well is being drilled. The goal of the containment operation is to capture wellbore fluids and hydrocarbons exiting the well, and divert them to processing vessels. This process involves subsea infrastructure and surface processing equipment, as well as the connection of flow lines and riser systems to create a temporary subsea production system. The capping stack may potentially serve as the interface to connect containment system lines that will divert the flow to the capture vessel. Otherwise, a containment structure (“top hat” or a “containment dome”) could be placed over the well to collect escaping hydrocarbons. The current industry containment systems are designed to handle oil flow rates up to 100,000 BOPD (barrels of oil per day) and 200 MCFD (million standard cubic feet per day) of gas. Hydrate inhibition chemicals could be used to prevent the formation of hydrates that can plug flowlines transporting the oil to the surface (see Section 2.2). Collected and processed liquids are then offloaded from the surface production vessel to crude tankers and taken to shore for utilization and

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Image
FIGURE 4.1 An illustration of source control activities.
SOURCE: BSEE.

disposal. An example of use of a containment structure to capture oil during the ongoing Mississippi Canyon, Block 20 (MC-20) oil spill is detailed in Box 3.4. Various components of the source control operations are illustrated in Figure 4.1.

As a permanent source control solution, a relief well could be drilled in parallel with capping and containment activities to intersect the incident well at some predetermined distance below the seabed and seal the well by injecting heavy mud and cement. A relief well is drilled in the same way as a regular well and is positioned at an appropriate distance from the incident wellsite to allow safe drilling operations and avoid interference with the source control activities. The distance between surface locations for the blowout well and the relief well can range between 500 feet and 3,500 feet. When the relief well intersects the target well, drilling mud is pumped into the well to increase hydrostatic pressure and regain control of the well. When the well is no longer flowing, cement can be pumped into the well to seal it. Izon et al. (2007) analyzed the Mineral Management Service (MMS) data for blowout wells in the outer continental shelf of the United States in a period from 1971 to 2006. They found that out of 39 blowouts that occurred during that period, relief wells were initiated for two of them, because they were controlled by other means prior to completion of the relief wells. During the Macondo incident, well control was also regained through installation of a capping stack before completion of a relief well. Since then, there has been progress in making well control devices, such as capping stacks, more readily available for incident response.

Human factors are an important aspect of safe drilling operations and effective source control. In the United States and Canada, regulators require professional certifications as well as frequent drills and exercises to ensure personnel qualification, drilling safety, and response readiness. These include exercises with drilling crews to test their ability to detect and mitigate simulated influx of hydrocarbons, a requirement for rig supervisors to take a certified well control course every 2 years, conduct safety seminars, and Drill the Well on Paper (DWOP) exercises prior to the start of a drilling program. An important human factor component to safety on the rig is a broadly accepted industry practice, called “stop work authority,” where anyone has the right to stop the work if he/she feels that it is unsafe, without repercussion. This enables rig personnel to immediately stop unsafe operations without delays that may be caused by the need for managerial approvals. Additional discussion on human factors related to offshore operational process safety can be found in the proceedings of the 2018 National Research Council (NRC) workshop, The Human Factors of Process Safety and Worker Empowerment in the Offshore Oil Industry: Proceedings of a Workshop (NRC, 2018).

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

4.1.3 Pipelines

Although pipelines are specially designed, built, installed and operated to safely move hydrocarbons, an integrity failure may potentially occur resulting in a loss of product. Typical causes for such a failure include human error, such as anchor drags or misinterpretation of the control equipment readings and/or alarms, pipeline corrosion, process defects during installation, and flaws occurring during the manufacturing process, as well as geophysical external factors. Pipelines associated with oil and gas exploration are regulated by the U.S. Department of Transportation’s (DOT’s) Pipeline and Hazardous Materials Safety Administration (PHMSA) as well as by the BSEE. Industry employs pipeline safety management systems (SMS) (ANSI and API, 2015; API, 2019b) to significantly reduce the risk of incident occurrence as well as an incident’s impacts on people and environment. This approach goes beyond operational leak detection and also includes risk management, safety assurance, incident investigation, lessons-learned sharing and continuous improvement, staff competence maintenance, and emergency preparedness and response, among others.

Pipeline integrity monitoring allows an early detection of structural issues and repair or replacement of the impacted segment before loss of integrity and a potential leak. Leak detection techniques allow quick shut off to stop hydrocarbon discharge and reduce the lost volume and environmental consequences due to the pipeline failures. A variety of pipeline monitoring and leak detection techniques and approaches have been developed over the years, resulting in a decrease of pipeline-related incidents and their consequences. Some of them aim to detect the leak at the exterior of the pipeline, while others use devices, sensors, and computational algorithms (API, 2007) to monitor pipelines from the inside.

For offshore use, leak detection techniques include acoustic detection, fiber-optic sensors, pressure point analysis, rate of change / conditional rate of change, dynamic modeling, vapor sampling, infrared thermography, digital signal processing and mass-volume balance technique, among others (DNV, 2016; Adegboye et al., 2019). Additional techniques can be employed onshore; for example, the use of ground-penetrating radars, spectral scanners, or specially trained dogs that can detect a leak as deep as 15 feet (API, 2016a). Pipeline integrity can be assessed by smart pigging, an in-line monitoring technique employing sensor-equipped probes that are propelled through pipelines for cleaning and inspection activities. Additionally, remote leak monitoring can be conducted by sensors installed on autonomous underwater vehicles (AUVs), remotely operated vehicles (ROVs), or drones, or by using sensor networks. Recent advances in using AUVs and ROVs for subsea pipeline inspection and monitoring have significantly expanded offshore monitoring capabilities and reduced the risk of human exposure and errors. These systems can be operated remotely making them suitable for inspections in potentially hazardous environments such as deep-water and Arctic regions (Ho et al., 2019).

It is important that pipeline inspection and monitoring be considered as a system that is composed of personnel, procedures, and technologies. All three components must be addressed to assure pipeline integrity. In addition to the development and deployment of robust monitoring and detection technologies, development and implementation of human controls is also important. These may include performance metrics and key performance indicators, control center procedures, competencies and responsibilities of personnel, training and exercises, among others (API, 2015c, 2019c; 49 C.F.R. pt 195).

4.2 RESPONSE

4.2.1 Introduction

Oil spill scenarios, their potential impacts, suitable response options, and the effectiveness of those options vary greatly from spill to spill. Over the past several decades, the trend has shown the volume and the number of spills have been declining over the years (see Chapter 3). Most spills are fairly small, are in the industrial areas close to response equipment depots, and can be effectively responded to (e.g., by mechanical recovery) without the need for complicated equipment and comprehensive analysis. Fewer spills—for example, large spills in offshore or coastal areas or spills in particularly sensitive environments—may require a larger number of Incident Command System (ICS) managers and numerous responders, focused engagements with stakeholders, a detailed environmental and operational analyses, and the use of complex response strategies and monitoring techniques. This section aims to review various oil spill response tools that have a potential to reduce the volume and impacts of the released product and which could be considered for response in marine environments. It is important to note that no single response technique is absolutely effective, safe, or even applicable or necessary in every situation. The benefits, scenario-specific effectiveness, operational challenges, and any potential additional environmental and socioeconomic impacts of any tool use have to be carefully considered using best available expertise and information before a decision to proceed is made.

4.2.1.1 Response Structure

In the 1970s, California was devastated by a series of catastrophic forest fires encroaching on urban turf. As part of an effort to determine the cause of this disaster, case histories were examined and it was discovered that incident failures were far more likely to result from inadequate management than from lack of resources, faulty tactics, or any other factor.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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It was from this insight that ICS was born. ICS represents organizational “best practices,” and has become the standard for emergency management across the United States (HSPD 5, 2003). ICS provides a common management structure through administrative support and oversight in a response to create time- and resource-efficiency between management personnel from various agencies. ICS is interdisciplinary and agile by design so as to meet the needs of various agencies and various incidents. ICS has been tested in more than 30 years of emergency and nonemergency applications, by all levels of government and in the private sector (NPS, 2017).

Walker et al. (2015) define formal authorities involved in the response structure as including agency representatives having oil spill authority at multiple levels of government and potential parties responsible for making and implementing preparedness and response decisions to mitigate impacts to the ecosystem and the ecosystem’s resources, users, and property owners. Stakeholders are identified as “part of a community and broadly defined as those groups that have a stake, interest, or right in an issue or activity (e.g., an oil spill) and those that will be affected either negatively or positively by decisions about the issue or activity” (Krick et al., 2005).

In the early 1990s the U.S. Coast Guard (USCG) modified the original ICS into its Incident Management Handbook (IMH) for use on oil spills, chemical releases, and other environmental and emergency responses. This became the de facto management system for response in the United States and has been adopted by many other nations and companies. Through training and certification, individuals are able to move from incident to incident and fill designated positions in the management structure (USCG, 2020).

The essential philosophical modification from strict ICS to a unified management system aligns with the Oil Pollution Act of 1990 (OPA 90) legislation where the responsible party (RP) is mandated to be the entity charged with source control, oil removal, and environmental restoration. This provides a regulatory role for the RP, along with the federal and state agencies involved in environmental protection. In an ICS chart, this would form the Unified Command triangle on the top of the ICS pyramid. As opposed to a Stafford Act response, where the government is wholly in charge of response activities to a natural disaster, an oil spill is more cooperatively managed, with the government providing oversight to the RP to direct cleanup activities.

Over the decades, after the Exxon Valdez (1989), with the incorporation of this modern response management system, response activities have generally become more cooperative and less combative at the corporate/governmental levels. To achieve the optimum outcome from a response, ICS helps ensure best management practices, streamlined organization structure, minimally environmentally intrusive tactics, and economically viable and socially accepted practices to most effectively plan for, respond to, and restore the environment after an oil spill occurs.

4.2.1.2 Common Operating Picture and Information Management Systems

The U.S. Department of Homeland Security’s (DHS’s) definition of a common operating picture (COP) is a continuously updated overview of an incident compiled throughout an incident’s life cycle from data shared among integrated communication, information management, and intelligence and information sharing systems (DHS, 2008). The goal of a COP is real-time situational awareness across all levels of incident management and across jurisdictions. This need was called out in the NRC’s Oil in the Sea III (2003) report recommendation for “federal agencies … to work with industry to develop and implement a rapid response system to collect in situ information about spill behavior.” Several COP systems have been developed over the years.

One such system, developed by the National Oceanic and Atmospheric Administration (NOAA) and the University of New Hampshire, with the U.S. Environmental Protection Agency (U.S. EPA), the USCG, and the U.S. Department of the Interior, is the Environmental Response Management Application (ERMA®) (NOAA, 2014a). This is an online mapping tool designed to act as a common operating picture that integrates both static and real-time data, such as Environmental Sensitivity Index (ESI) maps, ship locations, weather, and ocean currents, in a centralized format for environmental responders and natural resource decision makers. ERMA® enables a user to quickly and securely upload, analyze, export, and display spatial data in a Geographic Information System (GIS) map. ERMA® provides decision makers with the information needed to make informed decisions for response, damage assessment, and recovery and restoration efforts.

4.2.1.3 Classification of Coastal Environments and Environmental Sensitivity Index

The process of mapping of coastal environments and ranking their relative sensitivity was first used in 1976 for Lower Cook Inlet, Alaska (Michel et al. 1978). Since then, the coastal environment ranking methodology to aid/expedite response decision making by providing information about resources at risk has been refined and expanded to cover shoreline types throughout the world. ESI maps have been used for oil spill contingency planning and response since 1979. ESI maps provide a succinct visual summary of resources, such as birds, shellfish, drinking water intakes, corals, and coastal recreational areas, that are at risk if oil is spilled in that geographic region. ESI maps help responders and planners determine protection priorities in view of sensitive biological resources and human-use resources using specific symbol sets, icons, and hatch patterns (NOAA, 2019) (see Figure 4.2; see Appendix G for ESI map definitions).1

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1 See https://response.restoration.noaa.gov/resources/environmental-sensitivity-index-esi-maps.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Image
FIGURE 4.2 Example of ESI map.
NOTES: Shorelines on ESI maps are color-coded by sensitivity to oil. Symbols mark localized areas for biological and human-use resources.
SOURCE: NOAA, 2019.

In addition to the NOAA standards, modified ESI mapping methods have been developed in Europe (IOGP and IPIECA, 2012) by a joint effort of IPIECA (the global oil and gas industry association for environmental and social issues), the International Maritime Organization (IMO), and the International Association of Oil and Gas Producers (IOGP).

To archive and disseminate data after an incident, NOAA developed the Data Integration Visualization Exploration and Reporting (DIVER) system (NOAA, n.d.). This system allows users to search and download a wide range of environmental description and project planning data by geographic areas or incident activities. The DIVER tool provides natural resource trustees and the public with the ability to access, query, visualize, and download vast data on environmental pollution, sampling, and restoration efforts. ERMA® provides direct access to DIVER for data query and download.

The DIVER tool is an application for the integration and distribution of Natural Resource Damage Assessment (NRDA)-related impact assessment and restoration data. It also contains historical data collected from oil spills and hazardous waste sites around the country. The DIVER Explorer query tool allows public users to search, filter, access, and download available data. Deepwater Horizon (DWH) restoration projects and monitoring data are also incorporated into DIVER.

Significant increases in information gathered and generated during emergency response and natural resource damage assessment phases led to the need to store and process large volumes of data and corresponding metadata. Since the publication of Oil in the Sea III, there has been considerable improvement in information and computational technologies; further development is expected to progress at a fast pace in the coming years. The preceding examples are government-provided assets. Additionally, industry-developed electronic COPs and data management solutions used to augment or replace those mentioned earlier are also available. Please refer to Chapter 5 for the more detailed discussion on this topic.

4.2.1.4 Response Toolbox

There is a long list of response techniques and technologies that may be employed during an oil spill (see Figure 4.3). These methods include mechanical cleanup to remove oil, dispersing agents, in situ burning, various shoreline cleanup techniques, etc. (NOAA, 2013a; see Sections 4.2.2, 4.2.3, and 4.2.4). Using an analogy of a toolbox, one must choose the right tool(s) for the right job. If a piece of wood has to be trimmed, a hammer or screwdriver would not be the first choice of tools to undertake the chore. However, the toolbox would also include a saw, clamps, file, knife, etc., to accomplish the task efficiently. Similarly, depending on the type of oil, the location of the spill, water depth, water and air temperature, wind speed, time of day, precipitation, etc., the specific tools that are correct for the response will vary.

The other concept that must be factored into the choice of the best response strategies are environmental and socioeconomic concerns. Ideally, the response techniques chosen will do no further harm and will contribute to mitigating further impacts. The processes of net environmental benefit analysis (NEBA) (IPIECA, 2015) or spill impact mitigation assessment (SIMA) (IPIECA and IOGP, 2018) are used in the ICS Planning Section by the Environmental Unit to identify which tools in the toolbox are most suited to the specific situation (refer to Section 4.2.5 for more details). Monitored natural attenuation is usually a starting point

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Image
FIGURE 4.3 Oil spill response techniques and technologies.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

for weighing appropriateness of the actions, and can be the most appropriate approach. For example, a small to medium size spill of light fuel oil in an offshore area will probably evaporate quickly and may not require further response actions. Allowing the oil to naturally evaporate and biodegrade without application of additional response techniques could, under some circumstances, be the best-case solution.

To demonstrate the concept of tradeoff decision-making in identifying appropriate response actions, Figure 4.4 illustrates the generic “normal” fluctuations over time in the environment under conditions in the absence of a spill, and the potential gradual recovery time after an incident with no cleanup response actions, shortened recovery time with the application of cleanup options 1 and 2, and potential longer recovery time after cleanup option 3. Using a net environmental benefit analysis, Option 3 would most likely not be implemented. Eventually, with time and possible restoration activities, the response recovery lines will approach the conditions in the absence of a spill (blue line).

Oil spill response equipment may be owned by individual companies or by federal, state or local governments, but the majority of it is held by the oil spill removal organizations (OSROs). Following the OPA 90 and its requirement for certain U.S. facilities to have plans and equipment to respond to spills, various OSROs have been established. These organizations are voluntarily classified by the USCG. They are classified by the Captain of the Port (COTP) Zones by spill size, removal capacity, response times, and by different operating environments (e.g., rivers and canals, inland, great lakes, and oceans). These organizations are responsible for holding, maintaining, and deploying appropriate response equipment and trained personnel at the time of response as requested by their stakeholders. The USCG uses the Response Resource Inventory2 (RRI) to maintain a comprehensive list of spill removal equipment held by OSROs. It contains information about response resources (including ownership and location) in 12 equipment categories (boom, pumps, vessels, skimmers, dispersants, dispersant delivery systems, vacuum systems, beach cleaners, portable storage, oil/water separators, fire-fighting equipment, and logistical support equipment) and also tracks response-trained personnel. The RRI aims to improve the effectiveness of deploying response equipment to an oil spill, and may be used to develop contingency plans.

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2 See https://cgrri.uscg.mil/logon.aspx?ReturnUrl=%2f.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Image
FIGURE 4.4 A conceptual model of potential impacts and recovery over time as derived from modeling and experience considering several cleanup options as compared to pre-spill conditions or no response actions.
SOURCE: Adapted from NOAA.

4.2.1.5 Response Research and Development

The field of oil spill response has similarities to the medical profession. Both have professionals with advanced degrees and many years of practice. Both rely on science and experience for decision-making and advancement of knowledge. In each case, for operational application best restorative practices using the most appropriate available technologies are implemented. Researchers (academic, government, and industry) are at the forefront of discovery and innovation. Their laboratory results have to be tested and assessed prior to being implemented on a broad level in the field or general population. Each relies on a prescribed theory of triage to help prioritize the locations and types of treatment. There is a large cadre of individuals involved to assist at all levels of care to ensure the best outcome for the patient or environment from the activities pursued. There are numerous treatment options (tools in the toolbox) to choose from and while each of them has their benefits and tradeoffs, only options that are anticipated to produce positive results with minimal negative effects are implemented. Stakeholders (trustees or patients) have a voice in the process as to what may work best in a particular situation. Each individual and situation is unique and the treatment options vary from place to place and time to time as knowledge and technology improve.

The preferable time for doing oil spill response research and development is not during an actual emergency but rather in preparation for one. Government agencies (NOAA, USCG, the Bureau of Ocean Energy Management [BOEM], BSEE, Environment and Climate Change Canada [ECCC], Department of Fisheries and Oceans Canada [DFO], Texas General Land Office [TGLO], etc.), industry, private companies, nongovernmental organizations (NGOs), and academia have well-developed and administered programs: they are continually looking into improvements for response technologies, identifying the effects of oil on the environment, developing better ways to monitor oil in and on the water, and looking to increase the efficiency of response operations and organizations. These projects generally take place in a laboratory or test tank. To verify laboratory experiments in real-world conditions, in addition to modeling and reviewing data from previous incidents, field testing of different response countermeasures is needed. While laboratory experiments can be conducted with crude oils and petroleum products, receiving a regulatory approval for a field experiment with hydrocarbons has been a challenge.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

Researchers and responders attempted to simulate an oil spill in the field using various surrogates—popcorn, oranges, soy and canola oil mixtures, tree barks, food dyes, etc., but they found that the complexities of oil’s chemistry, fate and behavior discussed in Chapters 2 and 5 cannot be simulated using these substitutes. Field experiments with real oils and petroleum products are needed to further advance oil spill science and optimize oil spill response techniques. Use of novel experimental techniques are not generally approved during emergency response situations. However, in advance of an accidental oil spill, planning bodies (e.g., Area Committees and Regional Response Teams in the United States) could have mechanisms in place to allow “small science” projects to occur on a portion of a release to be able to make informed scientific measurements and conclusions on different products in collaboration with industry and academia.

To establish a uniform and impartial method to determine the level of development of new response technology, and to determine when it is ready for field use, BSEE has developed technology readiness levels (TRL) (see Table 4.1). These range from TRL 1, with basic science exploration for future technology applications to TRL 9, where the technology is deployed for a real spill (Panetta et al., 2016).

In order to help sift through the many new ideas and suggestions that may be presented to an incident commander during a response, the Alternative Response Tool Evaluation System (ARTES) (API, 2013a; NOAA, 2019b) may be implemented. ARTES allows a special response team to swiftly review proposed response tools and provide a recommendation to the on-scene coordinator. This system allows people who submitted response ideas to track their proposals and progress through the assessment process. During the DWH incident, 123,000 individual ideas were submitted and tracked; 470 made the initial cut, 100 of those were officially reviewed, and about 30 were executed during response field operations resulting in incremental improvements. Of the original 123,000 submissions, there were about 80,000 ideas submitted for subsea response and about 43,000 ideas for surface oil slick response. It should be noted that this process took tremendous effort and a significant number of personnel. Such evaluations require careful consideration in the context of specific response needs and resources available to make sure that evaluation efforts do not reduce overall efficiency of the response. Development of oil spill response science requires cooperative actions from industry, governmental agencies, and academia internationally. Many projects are conducted collaboratively through joint projects to ensure incorporation of the best available and diverse expertise and to facilitate the widest dissemination and adoption of new knowledge and technologies. There are a number of standing conferences, regular workshops and committees that bring together all interested parties and facilitate information sharing. The International Oil Spill Conference (IOSC) has taken place since 1969 and served as a primary venue for sharing and documenting oil spill research and best operational practices. All of the proceedings are available online free of charge at the International Oil Spill Conference Proceedings website.3 More recently, additional conferences moved to fill the tri-annual cycle with venues rotating among the United States (IOSC), Europe (Interspill), and Australia (Spillcon). Another long-standing venue is the Arctic and Marine Oilspill Program (AMOP). AMOP began in 1977 and still serves as a meeting place for oil spill and environmental scientists to share their experiences and ideas. The Industry Technical Advisory Committee (ITAC) has been organized annually since 1996 to bring together scientists, regulators, and spill response practitioners to discuss new developments in the field and facilitate their practical adoption in oil spill response operations.

TABLE 4.1 Oil Spill Technology Readiness Levels (TRLs) Used by BSEE for Research and Development Prioritization

TRL Title
Technology Research and Development
1 Basic principles observed or reported
2 Technology concept and speculative application formulated
3 Technology proof of concept demonstrated
Technology Advancement, Development, and Demonstration
4 Technology prototype demonstrated in laboratory environment or model scenario
5 Technology prototype tested in relevant environments
6 Full-scale prototype demonstrated in relevant environments
Technology Implementation in Operational Environments
7 Integrated technology tested on a large scale or in open water
8 Final integrated system tested in real or relevant environment
Technology Deployment in Real Spill Environment
9 Final integrated system deployed in real spill environment

SOURCE: Panetta and Potter (2016).

The Interagency Coordinating Committee on Oil Pollution Research (ICCOPR) is a 15-member body established by the Oil Pollution Act of 1990 to “coordinate a comprehensive program of oil pollution research, technology development, and demonstration among the federal agencies, in cooperation and coordination with industry, universities, research institutions, state governments, and other nations, as appropriate, and shall foster cost-effective research mechanisms, including the joint funding of the research” (ICCOPR, 2015). The American Society for Testing and Materials (ASTM) F20 Committee on Hazardous Substances and Oil Spill Response was formed in 1975 and is still developing and updating documents and standards relevant to hazardous substances and oil spill response. Other meetings and information-sharing sessions are organized through various research programs and agencies such as BSEE, USCG, TGLO, NOAA, the Coastal Response Research Center,

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3 See https://meridian.allenpress.com/iosc.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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the Oil Spill Preparedness Regional Initiative, ECCC, DFO, the Canadian Association of Petroleum Producers, API, IPIECA, ITOPF, the American Chemical Society, U.S. Navy, etc. Additionally, there are focused multi-year, multidisciplinary research programs with a fixed timeline for funding, such as the recently completed Gulf of Mexico Research Initiative program in the United States and the ongoing Multi-partner Research Initiatives program in Canada. An X Prize competition, such as the Wendy Schmidt Oil Cleanup XCHALLENGE, is another example of a funding mechanism fostering innovation on a specific response topic. All of these programs have generated invaluable advances in oil spill response knowledge and technologies and facilitated global sharing and deployment of this information.

4.2.2 Monitoring and Assessment

Over the past two decades, significant advances in sensing instrumentation have occurred. These smarter, more sensitive, broader-spectrum, smaller, and more varied devices can now track spills from above and below the ocean surface as the oil spreads and moves through the environment. We consider monitoring and assessment platforms to be the systems that maneuver sensors through the environment. Sensors themselves make and record observations. In general, multiple sensors can be installed in any observing platform, and many sensors are suitable to multiple platforms. This section is organized by considering the different platforms deployed for monitoring and assessment. Platforms available in the toolbox for deploying sensors for oil visual and chemical observations include moored instruments, equipment casts from the vessels, subsurface and surface vessels (including manned and autonomous), aircraft, and satellites (API, 2013a; IPIECA, 2016; Fingas, 2018; IPIECA, 2021).

A new essential component of oil spill response is remote sensing. It is the science of obtaining information about areas or specific objects from a distance, typically from aircraft, vessels or satellites. The public expectation is that remote sensing now allows for the precise mapping of oil spill extent and location. However, in a practical sense, the ability to accurately map oil either on or in water is not fully achievable, especially in the water column. Whether remote or in situ sensors are used, the observations must be geolocated. Response personnel can use location information to implement countermeasures to minimize the effect of pollution. Remote sensing can also provide information about illegal discharges from ships (Fingas and Brown, 2018). For a given mission, a combination of remote sensing systems may be needed. Different data end-uses, including documentation of spill location, enforcement or cleanup support, or documentation of affected resources, may require a specific and differing characteristics of the data such as resolution. Remote sensing data collected during the response phase can also be very valuable for the NRDA phase.

Figure 4.5 illustrates a variety of remote sensing platforms that may be involved in oil spill surveillance.

4.2.2.1 Surface Oil Detection and Monitoring

Aerial and surface remote sensing is used in spill response for several types of missions:

  • Oil on Water Observations:
    • Mapping and documentation of the area, slick thickness, and percentage cover in time and space
    • Verification/“ground-truthing” of satellite imagery and modeled trajectories
  • Support to Tactical and Strategic Countermeasures:
    • Identify most suitable areas of the slick for mechanical recovery, in situ burning, and surface dispersants
    • Monitor effectiveness of response strategies including monitored natural attenuation
  • Resources at Risk Observations:
    • Monitor and document presence and absence of wildlife in the area
    • Monitor environmental, socioeconomic, and cultural resources at risk
  • Shoreline Cleanup Assessment Technique (SCAT) Support:
    • Aerial surveillance of the shoreline to document baseline conditions
    • Aerial surveillance of the shoreline to document and quantify oil on the shorelines

In addition to response activities, remote sensing could also be used to gather information related to the NRDA; for example, documentation of pre-impact baseline conditions at reference sites, documentation of impacts, as well as progress of restoration projects. These above missions could be delivered through a variety of remote sensing platforms.

Aircraft

A trained observer in an aircraft, either a helicopter or fixed-wing platform, can be rapidly deployed to provide feedback concerning the location, surface coverage, movement, physical description of the product, surrounding environmental and wildlife concerns, and qualitative assessment of volume. Limitations on this method include the platform operating parameters (weather, altitude, light, etc.), ability to see a limited area at a time, darkness, cloud cover, and sun glint. With the current technology, aircraft can plot exact locations (using GPS) of observed oil and other features of concern, map the outline of slicks, transmit the observations (in near real time), and give a human analysis of the situation.

Cameras with GPS can capture images for display in the command post to show examples of the types and degree of oiling and other concerns. These images can also be used as evidence in post-incident legal matters. Both still and video images are useful. Light-enhanced (night-vision) cameras can be used in the dark to help identify oil.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Image
FIGURE 4.5 Remote sensing platforms where sensors can be placed for oil spill surveillance.
NOTE: AUV = autonomous underwater vehicle; ROV = remote operated vehicle; UAV = unmanned aerial vehicle; UUV = unmanned underwater vehicle.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

Sensing instrumentation used from an aircraft typically include synthetic aperture radar (SAR), Side Looking Airborne Radar (SLAR), U-cameras operating in ultraviolet (UV), visible and infrared (IR) ranges, and laser-induced fluorosensors. The API Planning Guidance for Remote Sensing in Support of Oil Spill Response (2013) and the paper by Fingas and Brown (2017) provide detailed overviews of various sensors, their strengths, limitations, and operational conditions. Sensors such as IR sensors are referred to as “passive” sensors because they passively detect slick radiation, as opposed to “active” radars or laser fluorosensors that emit energy for slick detection. The difference in oil slick emissivity, heat capacity, and thermal conductivity compared to the surrounding water allows observers to distinguish it using UV/IR sensors during day or night. Figure 4.6 illustrates the difference in slick mapping done by IR and UV sensors. UV sensors tend to map the entire extent of the slick including thin sheen, which is helpful for the environmental impact assessment, where IR sensors map thicker portions of the slick, which helps to direct response resources to the areas where they can be most efficient.

Radar techniques can operate day and night and under cloud cover. They detect the capillary waves on the sea surface and any dampening effect produced by the floating oil. As there are multiple substances that can cause this dampening effect, these images must be verified to confirm presence of a slick. Although not frequently used due to logistics constraints, laser fluorosensors can detect oil by emitting laser light and detecting the fluorescence emitted by the hydrocarbons. Because different substances emit fluorescent light at different wavelengths, this technique allows one to discriminate between different types of oil and other materials that may be present on the water surface or shoreline.

There are modern advanced multispectral and hyperspectral systems that integrate the feed from multiple sensors for maximum detection accuracy. Because no one sensor is 100% effective in every spill scenario, it is important to have access to multiple remote sensing tools for optimal data collection and interpretation suitable for various missions. Several government-owned and commercial planes offer integrated solutions with a variety of sensors that allow tailoring of data acquisition and processing to a specific scenario and data needs.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Image
FIGURE 4.6 Examples of oil slick mapping using UV sensor (left), IR sensor (middle), and a fusion of both images (right).
SOURCE: Fototerra Aerial Survey, LLC.
Aerostat or Balloon

Usually tethered to an oil spill response vessel (OSRV), an aerostat or a balloon may carry passive remote sensors similar to those on an aircraft, including optical and thermal infrared camera systems. These systems may improve the OSRV’s response ability to locate and position the vessel to best contain and remove the thickest oil, thereby maximizing response and recovery operations.

Unmanned Aerial System or Drone

These platforms have been used for both shoreline surveys and open water reconnaissance. Currently, in the United States, drone flights have to remain line-of-sight operations (except with waivers from the Federal Aviation Administration [FAA] or for the U.S. Department of Defense). This may be an impediment to their larger operational use. Depending on the platform size, the weight and dimensions of the attachable instrumentation may be limited. They may be fitted with one or multiple of the previously described instruments.

Vessel

Some of the X-band marine navigation radars used on the vessels can be reconfigured and accompanied with data processing software to map a slick in proximity to the vessel. Just as other radars do, it detects the areas with dampened capillary waves due to slick presence.

Satellite

Satellite remote sensing tools and best practices have been reviewed in several publications (Partington, 2014; IPIECA, 2016). Satellite imagery can provide the outline or footprint of the extent of surface oil. However, having the outline does not provide detailed information about oil coverage, as oil slicks are patchy with great variability in the thickness of the oil. The outline of the oil slick does inform on scene observers to collect additional information. Analyses using accrued knowledge of slick behavior and visual interpretation of images are starting to allow remote sensing to define not only the extent but also identify the thickest parts of the slicks (Garcia-Pineda et al., 2020).

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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The application of visual satellite images for oil spills has been undertaken over the past few decades. QuickBird, WorldView I and II, GOES East (GOES-16), and GOES West (GOES-17) now provide recurrent satellite coverage of the Earth’s surface. Various wavelength data from multi-spectral satellites (MODIS and MERIS [Medium Resolution Imaging Spectrometer]) provide additional, new, means of Earth observation. Detecting oil spill from remote sensors in the visible spectrum depend on weather conditions, oil types, and view angles. Cloud cover and sun glint inhibit detection in visible imagery. Sun glint is often severe and can obscure an entire scene; however advances to remove sun glint have been made. Several visual imaging systems were employed during the DWH spill. A multi-spectral image derived from MODIS was corrected by an automated classification system to improve the image and classify oil on water. (Fingas and Brown, 2018).

The Marine Pollution Surveillance Report (MPSR) (see Figure 4.7) is a product package, generated in the NOAA National Environmental Satellite, Data, and Information Service (NESDIS) Satellite Analysis Branch (SAB), when a marine anomaly is identified in or approaching U.S. waters and believed to be the result of an accidental or intentional oil discharge. Most often potential oil slicks are detected through the analysis of multispectral satellite imagery and synthetic aperture radar, but are sometimes identified through other surveillance means such as aerial photography. Anomalies are identified based on visual inspection, and through the use of various auxiliary datasets including an automated oil spill mapping tool. Visible imagery is advantageous because different color combinations can be analyzed to distinguish oil from vegetation. Radar imagery is advantageous because it can “see” the surface of the ocean during night time hours and through clouds.

Satellite SAR (image resolution of order 10 m) has been used to define areas containing oil and as “oil free,” additionally it allows for identification of oil emulsions within an oil slick and rapid classification of oil types.

Image
FIGURE 4.7 Satellite image with annotations.
SOURCE: NOAA NESDIS.
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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SAR imagery provides information about thick oil and oil emulsions (i.e., “actionable” oil) that can quickly aid responders in the field. At the Ohmsett (the National Oil Spill Response & Renewable Energy Test Facility in New Jersey) experiments determined that during certain viewing conditions, differences can be detected between thick stable emulsions and non-emulsified oil using a single polarization SAR image when taken from a sensor at elevation (Garcia-Pineda et al., 2020). Novel remote sensing methods have the potential to be used for oil spill responses by providing fast information to emergency responders. It is important to note that the data outputs are instrument-dependent because the sensitivity of the instruments is highly dependent on the analysis of backscatter in different frequency bands and different methods for noise elimination. At this time, these experimental technologies allow the comparison of relative oil thickness, but are not sensitive enough to quantify specific volumes.

Aerial images and satellite images can be used for tracking the oil as it moves at sea. The time lapse imagery from the MODIS (Moderate Resolution Imaging Spectroradiometer; resolution ranging from 250 m to 1,000 m) instrument, on board NASA’s Terra and Aqua satellites, was used after the DWH spill for tracking the oil slick (which appears grayish beige in Figure 4.8 and is altered by changing weather, currents, and use of oil dispersing chemicals). Terra MODIS and Aqua MODIS view Earth’s entire surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of

Image
FIGURE 4.8 Satellite images of oil after the DWH spill, acquired on May 24, 2010.
NOTES: These images were captured by the multi-angle imaging spectroradiometer (MISR) instrument. The left-hand image contains data from MISR’s vertical-viewing camera. It is shown in near-true color, except that data from the instrument’s near-infrared band, where vegetation appears bright, has been blended with the instrument’s green band to enhance the appearance of vegetation. The right-hand panel was constructed by combining data from several MISR channels. In this false-color view, oil appears in shades of inky blue to black; silt-laden water due to runoff from the Mississippi River shows up as orange, red, and violet; and land and clouds appear in shades of cyan.
SOURCES: NASA/GSFC/LaRC/JPL, MISR Team. https://www.nasa.gov/topics/earth/features/oil20100602.html.
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

wavelengths. Recently, a new breed of tiny, modular satellites (Cubesat) offers a wide variety of imagery, depending on the location, with resolutions up to 5 m.

4.2.2.2. Oil Detection and Monitoring in the Water Column

A comprehensive monitoring program is critical to effective oil spill response (Payne and Driskell, 2015). Several recent publications, including the IPIECA/IOGP Good Practice Guide for in-water surveillance of oil spills at sea (IPIECA, 2016), describe tools and processes used to monitor oil spill fate and behavior in the water column (see Section 2.1.7). Generally speaking, water column monitoring involves the following tools deployed from different platforms, as shown in Figure 4.5.

Vessels

Vessels may house both sensor systems and other sensor platforms. Sensing systems may include visual reconnaissance and camera and video systems to observe surface floating oil, air quality monitors, continuous flow-through water quality analysis, and acoustics-based observing systems, such as sonar (split-beam and multibeam) and acoustic doppler current profilers (ADCPs). Sensor platforms fixed to the boat include conductivity, temperature, and depth (CTD) profilers and ROVs, discussed separately later in this chapter. Vessels thus provide a mobile hub for bringing experts, sensing systems, and sensors to the spill site and the affected area.

Split-beam and multibeam sonar are traditionally used to measure seafloor bathymetry, subsurface properties, and large pelagic organisms (e.g., fish). In oil spill science, sonar may also be used to observe oil droplets or gas bubbles as they traverse the water column. Oceanographic sonar is characterized by its insonification frequency, with lower frequencies being able to traverse longer distances. Lower frequency sonar also has longer wave-length sound forms. Objects smaller than the acoustic wave length typically are not observable by sonar and are considered acoustically transparent. Gas bubbles are an exception to this rule as the bubble-water interface is excited by a wide range of typical sonar frequencies, emitting a loud signal despite the bubbles being smaller than the acoustic wavelength (Weber et al., 2014). In contrast, oil droplets, which have densities similar to sea water, remain acoustically transparent to sound waves with wavelengths greater than their diameters. Hence, multibeam sonar has become a major tool for observing natural gas seepage in the oceans. Oil droplets may be observable in short-range, high-frequency sonar, but are less evident in long-range, low-frequency data (see Section 5.3.1 for more on natural gas seeps).

ADCPs are used to measure water currents in integrated bins over a profile under a ship. ADCPs can be mounted in a vessel hull or incorporated into other observing platforms (e.g., ROVs or moorings, described in the following text). ADCPs differentiate themselves predominantly by frequency, with the lowest-frequency ADCPs penetrating to about 1,100 m depth. Data are reported within fixed depth bins. Some floating oil and gas exploration and production platforms also include ADCPs, and these data are often uploaded in real time to public repositories. Especially in the nearfield of a subsea release, measured currents using ADCP are extremely beneficial to response modeling.

Aromatic hydrocarbons, which are highly fluorescent, are often a major constituent of typical crude oils; therefore, fluorescence techniques can be used to detect oil. These techniques typically excite oils using ultraviolet wavelengths (300–400 nm) causing fluoresce in the visible wavelength range from 400–600 nm. The specific fluorescent traits are determined by the individual compound’s carbon structure. The addition of additives will also alter the fluorescence characteristics of oils.

Ambient ocean properties are commonly measured using a sensor package that records conductivity, temperature, and depth (pressure) (CTD). These sensor platforms often also house a wide array of other sensors and may be deployed with additional sampling equipment. The CTD package is deployed from a wire connected to a spool on the ship deck and controlled by a deck computer. Conductivity, temperature, and depth are observed to produce density profiles of the ocean water column. Other sensors often integrated with the CTD include oxygen sensors, fluorometers calibrated to observe aromatic hydrocarbons, dissolved organic matter, phytoplankton, or other fluorescent constituents, and transmissivity sensors, among others. These sensors may be deployed together with a rosette system for collecting water samples in specialized bottles (e.g., Niskin bottles) throughout the water column.

Buoys

Buoys can be either stationary or free-floating. Stationary buoys provide fixed, moored platforms for deployment of various sensor packages. Many buoys are operational, providing continuous, real-time or near real-time monitoring of ocean properties. Others may be deployed strategically as part of a spill response. Generally, a stationary buoy consists of an anchor weight and a buoyancy package providing upward tension on a line between the anchor and buoy. A buoy cable may extend to the sea surface or may be suspended anywhere in the water column. Most sensors attached to buoys are located at a fixed point, attached to the buoy or buoy wire. Sensors include those described earlier for CTDs, ROVs, or AUVs. They may also include point current meters, wave sensors, and weather stations. ADCPs may be mounted near the surface profiling downward or in the water column profiling either upward or downward. Some complex buoys also include a wire walker that con-

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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tinuously moves a CTD up and down through the ocean water column.

Drifters

Floating buoys or tracking buoys (drifters) are designed to float together with an oil slick. They may be powered by a battery or solar power and may include satellite telemetry to help track an oil slick trajectory over time. Two broad classes of drifters are utilized in ocean sensing: surface floating drifters and sub-surface drifters. Subsurface drifters achieve neutral buoyancy at a selected isopycnal depth and rise to the surface occasionally to transmit their observed data. More than 2,000 such floats are continuously monitored around the globe. Surface drifters have a surface float and data communication system, sometimes attached by a tether to a subsurface sail, designed to track surface slicks (no tether and sail) or the currents at a given depth near the sea surface (with tether and sail), usually within 1 to 2 m water depth. Economic, biodegradable surface float technology has grown significantly since the DWH oil spill through research focused on circulation in the Gulf of Mexico (Özgökmen et al., 2016; Dannreuther et al., 2021).

Remotely Operated Vehicles

ROVs are deployed from a ship and continuously powered and controlled from a ship-board control room connected to the ROV over a wire tether. ROVs come in a wide array of sizes and are built for a multitude of purposes. In oil spill response, ROVs may be used downstream of the spill to monitor the ocean water column or within the response zone to conduct subsea operations, including subsea dispersant application. ROVs used in monitoring normally carry a high-definition video camera and other sensor systems similar to those installed on CTDs or ship vessels, including sonars and ADCPs. Because ROVs may be large and provide significant power subsea, they may also be integrated with more sophisticated sensors, including mass spectrometers and gas chromatography/mass spectroscopy (GC/MS) systems, though these sensors can generally be integrated with any platform that can provide enough space and power (Chua et al., 2016). Two advantages of an ROV over a CTD or AUV (see next heading) are that the operator has real-time video footage of the sample location and that the sensor platform can be piloted to enable sampling of specific locations.

Because ROVs can be maneuvered using real-time video feeds, they are an ideal platform for installing sensors designed to observe oil droplet and gas bubble size distributions. During the DWH oil spill, oil droplet sizes were measured by water samples collected from CTD Niskin bottles on a vessel deck and using an under-water holographic camera in the subsurface intrusion several kilometers from the wellhead (French-McCay, 2015). Niskin samples were analyzed using bench-top laser in situ scattering and transmissivity (LISST) instruments. This general technology uses the scattering of light by small particles to infer a particle size distribution. Current instruments can be deployed to great ocean depths and measure particles 500 microns in diameter and smaller. The LISST does not include a visual image; hence, additional observations are needed to ensure that the measurement corresponds to oil droplets. Other size distribution measurement methods utilize cameras. To avoid parallax error, a recent advancement utilizes collimated light to produce silhouette images with a camera (Brandvik et al., 2021). This has the added advantages that it may observe droplets or gas bubbles larger than 500 microns, does not assume that fluid particles are spherical, and can distinguish among gas, oil, and non-hydrocarbon particles (e.g., marine snow). Although an ROV may be the best platform to maximize effectiveness of these instruments, they can be deployed on CTD, AUV, and other platforms during response.

Autonomous Underwater Vehicles

AUVs include a wide range of platforms designed to carry out their missions autonomously, not connected to a ship or controlled in real time during their sampling. AUVs are mainly distinguished by their propulsion mechanism. Gliders move by adjusting their buoyancy such that they alternate between sinking and floating and by hydrofoils that produce horizontal motion from their vertical descent and ascent. Wave gliders likewise use the upward and downward motion of ocean waves to produce horizontal motion. Propeller-driven systems rely on battery power for most of their propulsion. These systems may carry sensors similar to those on CTDs and ROVs. AUVs are further outfitted with inertial navigation systems, communications systems, and the ability to carry out autonomous surveys. Over the past decade, advancement in autonomous vessels has increased rapidly, including improvements to navigation control and safety (Gu et al., 2021). Recent advances employ machine learning and on-board sensors to produce adaptive surveys. Long-range AUVs, such as gliders, receive new instructions over remote communications at intervals. Short-range AUVs conduct a survey and then surface, transmitting their location for pick-up.

The development of AUV technology for sea patrol and environmental monitoring included structural design, hardware and software design equipped with oceanographic sensors, surveillance cameras, and underwater cameras for several applications. Wireless communication with 2.4 GHz frequency has been utilized over short distances for monitoring, control, and real-time communication between a base station and the AUV.

Multiple AUVs were deployed during the DWH oil spill to observe and track the subsurface intrusion layer that formed near 1,100 m water depth predominantly to the west-southwest of the wellhead (Camilli et al., 2010; Zhang et al., 2011). Unique sensors are increasingly being

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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integrated with AUVs, including sensors like the in situ mass spectrometer deployed with the Sentry AUV during the DWH oil spill (Camilli et al., 2010).

Hundreds of oil and gas industry structures in the marine environment are approaching decommissioning (see Section 3.5.2). As decommissioning of these aged structures occurs environmental assessment and monitoring must be conducted and potentially lasting over the life of any assemblies left in place. One solution to the major oversight challenge is to use marine autonomous systems (MASs) to monitor the decommissioned structures. The acoustic, visual, and oceanographic sensors installed on MAS provide necessary data for decommissioning oil and gas structures (Crabb et al., 2019). MAS provide both the considerable potential for cost savings and a dramatic improvement in the temporal and spatial resolution of environmental monitoring. MAS offer viable alternatives where a direct match for the conventional decommissioning monitoring approach is not possible (Jones et al., 2019).

Bottom Samplers

Sampling platforms may also be installed at the seafloor. Some are transported by an ROV, such as a push-core sampler that retrieves seafloor sediments. Others are set in place and capture marine snow and sediment as it reaches the seafloor (e.g., a sediment trap).

Sunken Oil Detection

A specific case of oil monitoring in the water column is detection and mapping of heavy oil that is submerged in the water column or has sunk to the bottom. API developed a technical report and an operational guide (2016a,b) describing techniques for sunken oil detection and recovery. Some of the detection techniques include diver observations, observations with the camera from underwater vehicles, sonar systems, acoustic camera, towed and stationary sorbents, bottom samplers, laser fluorosensors, and water column sampling. Recent experiments have also evaluated the use of marine-induced polarization for oil detection in the water column (Wynn et al., 2017).

4.2.2.3 Oil Spill Detection Above and Under Ice

Arctic environment presents some unique challenges for oil detection and monitoring, such as short daylight hours during winter months, prolonged periods of fog, strong wind gusts, low temperatures, and presence of the snow and ice cover for a significant portion of the year. All these factors complicate and sometimes reduce the efficiency of remote sensing operations. Oil spills in the Arctic or ice-prone environments behave differently from oil spills in open water (see Chapter 5 for more details), which affects remote sensing techniques and strategies. Some of the tools that are used to monitor oil in open water can also be used in the Arctic to detect oil in open water, between, or on top of the ice. Presence of different ice types requires special considerations and different tools for oil detection. Puestow et al. (2013) provided a detailed review of the above-ice remote sensing techniques that can be used to map oil in low visibility and ice. Wilkinson et al. (2014) described the techniques that could be used for oil detection under ice using AUVs. Watkins et al. (2016) developed an operational guide for oil detection in ice-covered waters integrating information from the first two reviews.

Some of the unique tools used for oil detection under ice include ground penetration radar (GPR) deployed from the ice surface as well as a newer method to use it from a helicopter. Detection of oil under ice and snow using trained dogs has also been successfully demonstrated. Oil can also be detected from below the ice using sensors deployed from AUVs or ROVs. Figure 4.9 illustrates these techniques. Watkins et al. (2016) provide additional information on the applicability and effectiveness of these tools for various ice and oil distribution scenarios.

Some of the more experimental detection techniques include nuclear magnetic resonance (NMR), marine induced polarization (IP) (Wynn and Flemming, 2012), as well as C-band scatterometer (Firoozy et al., 2017). Experiments conducted at the U.S. Army Corps of Engineers Cold Regions Research Laboratory showed that marine IP could detect oil under and within frozen ice, floating on the water surface, and floating with broken ice. Marine IP sensors must be deployed in water to observe oil; hence, they may be deployed on moorings, integrated with CTD, ROV, or AUV platforms, or towed behind ships. Fingas and Brown (2015) provide additional information on detection techniques in ice and snow.

4.2.2.4 Special Monitoring of Applied Response Technologies

Since the early 1980s, the response community recognized a need for procedures to monitor response technologies used during oil spills. The increased reception to using dispersants and in situ burning (referred to as applied or advanced response technologies) in most regions of the United States came about because of technological advances. Throughout the United States pre-approval zones for dispersant and in situ burn operations are in place with pre-approval conditions, and requirements for monitoring rules. The Special Monitoring of Applied Response Technologies (SMART) establishes a monitoring system for rapid collection and reporting of real-time, scientifically based information, to aid the Unified Command with directing in situ burning or dispersant operations. SMART recommends monitoring methods, equipment, personnel training, and command and control procedures that manages the counterpoise between rapid response efforts and informed decision making (SMART, 2006).

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Image
FIGURE 4.9 Platforms and sensors for oil detection in ice.
NOTE: AUV = autonomous underwater vehicle; GPR = ground penetrating radar; OPT/LFT = optical and laser fluorosensor; ROV = remote operated vehicle.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

The SMART program was used to monitor the effectiveness of sea surface dispersant use during the DWH oil spill. To quantitatively measure dispersant effectiveness, samples of chemically and naturally dispersed oil where the ratios of total petroleum aromatic hydrocarbon (TPAH) and total petroleum hydrocarbon (TPH) (see Section 2.1.2) were compared, the results showed good agreement with SMART field assessments of dispersant effectiveness. The SMART analyses generated data about acute biological effects of value to the larger scientific community, in addition to the primary goal of providing near real-time effectiveness data to the response (Bejarano et al., 2013).

Monitoring a heterogeneous plume of dispersed oil droplets in very dynamic ocean conditions presents a number of challenges. First, the access of monitoring vessels to the location of aerial dispersant application may be limited by the exclusion zones set around spraying operations, so vessels may be challenged to quickly access the precise location requiring monitoring; second, a dispersed plume may be transported in a different direction than any remaining surface slick thus complicating its tracking; third, by the time surface dispersants are usually applied, aromatic compounds targeted by fluorometers could have evaporated or dissolved from the slick; fourth, in some situations dispersion may occur rapidly before a monitoring vessel arrives on location, or could be delayed due to high oil viscosity or low ocean turbulence. It is important that the readings obtained as a result of the SMART monitoring efforts are put into appropriate context and interpreted by experts. These and other challenges prompted the ongoing development of updates to the SMART equipment and monitoring protocols to optimize its effectiveness and incorporate latest technologies.

4.2.2.5 Shoreline Cleanup Assessment Technique

Shoreline Cleanup Assessment Technique (SCAT) is a systematic method for surveying an affected shoreline after an oil spill to document shoreline oiling and monitor effectiveness of response techniques. The SCAT method originated during the response to the 1989 Exxon Valdez oil spill, when responders needed a systematic way to document the spill’s impacts on many miles of affected shoreline (NOAA, 2013b).

The SCAT approach documents shoreline oiling conditions by using standardized terminology. The use of standard oiling condition terminology supports decision-making for shoreline cleanup. SCAT is flexible in the scope of its surveys

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

and detail of datasets collected. SCAT is a regular part of oil spill response.

An initial assessment of the shoreline conditions require a SCAT surveys early in the response (see Appendix G), and ideally continuing in advance of operational cleanup. Throughout the response surveys continue to verify shoreline oiling and cleanup effectiveness, and eventually, to conduct final evaluations of shorelines to ensure that they meet cleanup end goals. SCAT survey teams are also trained to look for subsurface oil by digging trenches in locations where oil burial is likely.

The SCAT process includes eight basic steps (NOAA, 2013b):

  1. Conduct reconnaissance survey(s).
  2. Segment the shoreline.
  3. Assign teams and conduct SCAT surveys.
  4. Develop cleanup guidelines and endpoints.
  5. Submit survey reports and shoreline oiling sketches.
  6. Monitor effectiveness of cleanup.
  7. Conduct post-cleanup inspections.
  8. Conduct final evaluation of cleanup activities.

According to Michel and Ploen (2017) many natural materials could be mistaken for oil (e.g., algal blooms, suspended sediments, bacterial sheens), leading to the need for ground truthing aerial observations. A non-petroleum sheen and petroleum sheens act differently when disturbed, which cannot be conducted from aerial observation. Disturbing a bacterial sheen causes it to separate into small platelets or break like broken glass. A petroleum sheen, on the other hand, swirls and quickly reorganizes after being disturbed. Other techniques to differentiate non-petroleum sheens include:

  1. Hexane test, where the sheen is collected with a sheen net. The net is inserted into a glass vial containing hexane, shaken, and allowed to stabilize. A petroleum sheen dissolves in hexane, causing the hexane to discolor. Biogenic sheens do not dissolve in hexane, so there is no change in color.
  2. Ultraviolet test, in which hexane vials are viewed under ultraviolet light. Petroleum oils fluoresce, whereas biogenic sheens do not (EPA, 2016).

Final SCAT data and documentation should be input and archived into robust computer databases such as the ERMA® and the DIVER system.

Canine SCAT

Since the publication of Oil in the Sea III (2003), the use of canine detection of oil buried in the sediment or under ice has demonstrated improved effectiveness and efficiency of oil spill assessment surveys and leak detection. The methodology continues to be refined and improved as it is used in real oil spill situations, and as our understanding of how and what the dogs are actually detecting increases (API, 2016a).

A canine detection team can be deployed in a variety of field roles, which increase the speed and efficiency of SCAT surveys, improve the level of confidence in oil detection and delineation and provide more timely information for the planning and direction of response efforts. For more in-depth information and an overview that includes 2020 field trials, see Owens and Bunker (2021) and Owens et al. (2021).

Underwater SCAT

There have been several incidents (i.e., DWH, M/T Athos I [see Box 4.1], TB Morris J. Berman, and TB Vista Bella) where oil has become submerged in the nearshore area. Specially trained and equipped SCAT teams have been deployed to map the extent and concentration of oil. This methodology is referred to as underwater or snorkel SCAT. From the information gained thereby, cleanup strategies have been developed and deployed to areas where oiling warranted removal.

Electronic SCAT

The process of performing SCAT surveys has evolved over the decades, and in keeping up with modern practices several variations of electronic SCAT (e-SCAT) have emerged. These have been spearheaded by both governmental agencies and private enterprises. It is now possible to use digital pads or smartphones on shoreline surveys to mark locations, take photographs, fill in forms, read help screens, and upload data to command posts for decision-making determinations and archiving. The speed of data entry and increased accuracy of these digital platforms is a large step forward in the SCAT data management arena.

Drone SCAT

Over the past two decades the ability to remotely operate unmanned aerial vehicles (UAVs) or drones and the degree of precision and high-resolution imaging have greatly improved. Just as remote aerial surveillance can be used for tracking oil at sea (see Section 4.2.2.1), the use of drones to fly shorelines and identify oil has become more prevalent (Allen et al., 2008; Prascal et al., 2014; Tarpley et al., 2014; Muskat, 2021). Drones can access areas quickly, go where people may not be able to access, record images, and—with the aid of various lenses, filters, and artificial intelligence (AI)—be able to identify and interpret items that the human eye may miss. The use of drones is regulated by the FAA and is not appropriate in all situations. As the approach becomes less pioneering, the state of the art continues to evolve, and use becomes more commonplace, the integration of drones will probably become part of the standard SCAT team makeup. See Section 6.5.3.4 for additional examples by Kenworthy et al. (2017) for use of drones for ESI mapping.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

4.2.3 Offshore Response

4.2.3.1 Monitored Natural Attenuation and Biodegradation

Fate and behavior of hydrocarbons in the environment depend on their physical and chemical properties as well as conditions of the environment in which they were released. Natural attenuation (sometimes called intrinsic bioremediation) is a general term that refers to a combination of natural processes that decrease concentration of hydrocarbons in the environment, ultimately transforming and removing harmful components from the ecosystem (Pequin et al., 2022). These processes include spreading, evaporation, sedimentation, photooxidation, natural dispersion, and biodegradation (see Section 5.2.8). When combined with a regimen of sampling and measurement, it is called monitored natural attenuation. Biodegradation, which relies on microorganisms to convert hydrocarbons into less harmful components, is the ultimate natural attenuation process for removing hydrocarbon components from the environment. In general, light products such as gasoline, diesel, and condensate are not persistent in the environment, because of their high volatility, solubility, and natural dispersion and degradation rates. Typically, small spills of light crude oils are not very persistent, but their fate and behavior are strongly affected by environmental conditions. In warm climates and high seas conditions they may evaporate or naturally disperse within days. In cold climates, however, they could remain in the environment for weeks to months, especially if they freeze into ice or snow (see Section 5.3.5). Medium and heavy products are more persistent in any type of environment, and often require response efforts to mitigate their potential impacts.

The selection of an optimal combination of oil spill response options is made based on the environmental conditions, expected behavior of a spilled product, and resources at risk in the area. In some situations, it may not be safe or feasible to deploy spill response countermeasures. For example, a spill of a light product in high seas may evaporate or disperse naturally, not requiring an active cleanup. Even in calm conditions, light products may spread into very thin sheens that would not be feasible to clean up using mechanical recovery equipment, dispersants or in situ burning. These sheens would be expected to dissipate and degrade in a relatively short time frame. As long as they stay offshore and away from sensitive resources, natural dissipation and biodegradation may be the best “response” option. Although no active recovery operations would then be taking place in the field, identification of resources at risk, forecasting of surface and dispersed oil trajectory, remote sensing monitoring, sampling, and wildlife protection efforts could still be undertaken.

Natural attenuation processes are typically more effective in transforming oil at the water surface and in the water column rather than on the shoreline or in sediments. This is due to high dilution potential and abundance of oxygen and nutrients required for effective biodegradation (see Chapters 2 and 5). If hydrocarbons reach the shoreline or benthic sediments, they can potentially accumulate at higher concentrations in an environment less favorable for the effective removal of hydrocarbons. Even in those situations, it sometimes can be more ecologically sound to leave an oil-contaminated site to recover naturally rather than to conduct an active response. Some examples of such cases include spills at remote or inaccessible locations when oil properties and environmental conditions are suitable for effective natural attenuation or when conditions are too hazardous to risk human health and safety.

The safety of the public and responders is always the highest priority in any response operation. Depending on the spill scenario and environmental conditions, it may be impractical or unsafe to conduct containment and recovery operations. Not all products can be or should be recovered mechanically. Spills of very volatile products or blowouts with gas releases can create hazardous environments for the responders requiring them to leave the area or utilize personal protective equipment (PPE) and strategies that may reduce effectiveness of the response. Very light hydrocarbons (e.g., condensate and gasoline) evaporate rapidly and are typically allowed to do so naturally. They usually spread too thin to contain and could create a safety and exposure hazard if contained by a boom. If safe to do so, light, medium, and heavy hydrocarbon products could be recovered mechanically. Mechanical recovery has a wide window of opportunity and can continue to be effective even as an oil slick weathers over time. A variety of strategies and equipment have been developed specifically for the recovery of heavy and viscous products. Special recovery strategies have also been developed for the containment and recovery of heavy oils that may sink to the bottom (API, 2016d), although these operations would be even more challenging than oil recovery at the water surface.

Studies and field observations have shown that the relationship between oil and fine mineral particles in the nearshore area can play an important role in natural cleaning of contaminated marine shorelines (Lee et al., 2003b). The formation of micro-aggregates between oil and small suspended particles reduces the adhesion of oil to intertidal shoreline substrates and facilitates their removal by tidal action and currents through dispersion, dilution, burial in sediments, and biodegradation. In contrast, oil interaction with large sediment particles, such as sand, may form macro-aggregates and potentially cause oil to settle in nearshore waters as was evidenced during the DWH incident (Gustitus and Clement, 2017) (see Box 5.10 for more details). The latter scenario may require more active clean-up measures.

A spill of a light product that reaches a remote rocky shoreline with an energetic wave environment is not expected to persist and will degrade naturally as wave exposure increases both physical removal and weathering processes. It would not be feasible or safe to deploy recovery equipment

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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and personnel under these circumstances. Another example is a spill of a light product in a marsh area. Deployment of a large amount of equipment and personnel into this sensitive environment will likely cause greater impact by driving hydrocarbons into the marsh soil and destroying the root system of vegetation. It may be better to let attenuation processes remove hydrocarbons naturally rather than to conduct an invasive cleanup (Hoff, 1996). Natural attenuation as a shoreline cleanup method is typically still monitored to assess and document the effectiveness of this process.

Similar considerations are applied for the evaluation of natural attenuation potential of spills in cold climates. Under some circumstances, the presence of extended daylight time and local oil-degrading bacterial communities adapted to cold temperature could facilitate natural attenuation of oil at rates comparable to those in more temperate regions (see Section 5.3.5.2). This is especially true for light hydrocarbons and ice-free environments. Cold temperatures and ice filled waters can significantly affect the fate and behavior of medium and heavy hydrocarbons as well as the rate of natural attenuation processes, but can potentially create favorable conditions with an extended window of opportunity for other response options (Sørstrøm et al., 2010).

While bioremediation is sometimes used to remediate oil spills on shorelines, it is generally recognized that biostimulation (adding fertilizers) or bioaugmentation (adding lab-generated bacteria) are not appropriate methods for remediation of oil spills in the open marine environment (see Appendix E). It is well established that indigenous oil degraders, which exist in every marine ecosystem examined to date are adapted to the local conditions at any given spill site, whereas introduced microbes are at a disadvantage and may not compete with indigenous microbes (Hazen et al., 2016; McGenity, 2018). Also, adding laboratory-grown bacteria to the natural environment may be prohibited by local environmental regulations. Marine environments typically have sufficient quantities of oxygen and nutrients to support effective biodegradation of hydrocarbon products, as long as those products are present in small concentrations and offer substrate suitable for bacterial colonizations (e.g., very small droplets rather than thick emulsified slicks) (Zhu et al., 2001).

4.2.3.2 Mechanical Recovery

The containment and recovery of oil are often effective when responding to relatively small spills especially in calm waters or areas close to large stockpiles of equipment. Rapid deployment of equipment and personnel is critical for the success of mechanical recovery. Oil recovery at sea is always a race against time and natural physical processes which complicate the response. As soon as oil is released into water, it begins to spread and can form very thin sheens, thinner than a sheet of paper. It also breaks up into patches or windrows making it more difficult to collect and recover (see Section 5.2.2.1). Oil spill response vessels have to maneuver between these slicks and collect them into thicker layers to allow for more effective recovery by skimmers. Oil encounter rate—defined as the amount of oil accessed by a skimming system per unit of time—often determines the feasibility and effectiveness of mechanical recovery. Modern skimmers can process large volumes of oil, but it is the ability to collect enough oil in the boom and make it available for skimming that often determines how much oil can be collected in the field.

Mechanical recovery removes spilled oil from the water surface by relying on a complex system of devices and strategies, shown in Figure 4.11. First, remote sensing techniques are used to identify areas of recoverable slicks with a relatively high thickness. Oil on water does not spread uniformly and its thickness in different areas of a slick can vary greatly. These thicker areas generally occupy a relatively small portion of the total contaminated area yet contain the most oil volume. Mechanical recovery equipment deployed in the thickest patches of surface oil will be most effective and can potentially recover 100 times as much oil as can be recovered working on thin sheens. The next step of recovery operations is corralling and containing the oil. Because even the thickest areas of a free-spreading slick are too thin for effective recovery by oil skimmers, specially designed floating fences (booms) are towed by the vessels through the slick to corral oil into layers several inches thick. Skimming devices located in the thickest oil at the apex of the boom then separate oil from water and move recovered fluids into a temporary vessel storage before it is transferred to the shore for recycling or disposal. Mechanical recovery should be viewed as a complex multi-component system; removal efficiency depends on all components. This view is reflected in several calculators that aid in estimation of mechanical recovery system capacity and identification of any “bottlenecks” that could negatively affect its efficiency.4

Mechanical recovery was used for many years around the world under a variety of conditions. Most accidental releases of oil from a facility or vessel are small spills of less than 100 gallons (refer to Chapter 3 for more details). These spills often take place in industrial areas, ports, marinas, shipping lanes, and areas of general proximity to the response equipment depots. Depending on the type and volume of oil, the location and time of year, as well as resources at risk, the most appropriate response method is selected in consultation between regulators and the responsible party. For spills that are determined to require countermeasures beyond natural attenuations and monitoring, the responsible party will be required to activate its spill response plans and mobilize OSROs. OSROs will bring the required equipment

___________________

4 Response Options Calculator (ROC): https://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/response-options-calculator-roc; BSEE Response System Planning Calculators: https://www.bsee.gov/what-we-do/oil-spill-preparedness/response-system-planning-calculators.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Image
FIGURE 4.11 Mechanical recovery configurations.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

and personnel to clean up the spill while being monitored by the appropriate federal and state agencies. This could include sorbent materials, booms, skimmers, manual labor, vacuum trucks, etc. The incidents are usually dealt with and completed by a signoff from local, state, and federal authorities within days to weeks. Mechanical recovery can be very effective on small spills in calm waters and in areas where response can be assembled quickly, and will remain a preferred response technique for such situations.

Offshore conditions, large-volume spills, and remote areas present several challenges for mechanical response. Mechanical recovery is often favored by the general public based on the notion that a successful outcome of mechanical recovery is oil “removed” from the environment. In reality, and especially in when spills occur far offshore, or when winds or sea states are high, mechanical recovery may not be effective in recovering large volumes of oil. Historically, the “rule of thumb” has been that up to 10–30% of an offshore spill can be collected by mechanical recovery. A review of historical offshore oil spills found that mechanical recovery was only effective at removing between 2% and 6% of the total volume of oil spilled (Schmidt Etkin and Nedwed, 2021). During the Macondo response in the Gulf of Mexico, mechanical recovery removed only 3% of the spilled volume, despite an unprecedented number of personnel, recovery equipment, and vessels involved in the response (The Federal Interagency Solutions Group, 2010). The reliance on mechanical recovery alone for cleaning up large widespread offshore slicks may result in significant exposure of marine environment and its resources to potentially large volumes of unrecovered oil that continues to drift into new areas and may eventually reach sensitive nearshore and shoreline areas. Also, often overlooked are the impacts associated with the transport, treatment, and disposal of recovered fluids and debris (e.g., additional air contamination resulting from the waste transportation and disposal, potential contamination from the temporary storage sites, additional exposures of humans and wildlife to hydrocarbons, etc.).

Sea state is another major factor determining the feasibility of mechanical recovery. It can operate in short-period wind waves of up to 3–4 feet or in more developed “swell” waves not exceeding 5–6 feet. Higher wave heights cause equipment deployment and retrieval challenging, reduce the effectiveness of containment and recovery, and may reduce the safety of working conditions. In this situation, natural or chemically enhanced dispersion may become a valuable response tool. Because dispersion is most effective in the presence of waves, a significant portion of a slick is likely to be dispersed naturally under these conditions.

Because mechanical recovery efficiency is determined by the encounter rate of oil by a skimming system and the ability to recover it with minimal volumes of free water, recent technological improvements have focused on new boom designs

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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allowing for faster oil collection and improved skimmer designs, allowing the collection of larger volumes of oil with as little free water as possible. Conventional containment booms are limited to tow speeds of about 1 knot. Several new boom types use innovative designs to allow them to corral oil at higher speeds (Jensen et al., 2012). These systems modify the flow of oil and water in the containment area, allowing them to collect oil at 3 knots in flat water and 2 knots with light to moderate waves. Another innovation in booming optimizes mechanical recovery by using containment booms with fewer boats (Hansen, 2000). When deployed in water, this system behaves as a horizontal kite that pulls the end of the boom into the current and holds it at a fixed location relative to the towing vessel. This allows for one-vessel boom operation rather than needing two vessels to tow one boom.

Just as with car designs, some mechanical response systems resemble their earlier versions while incorporating major engineering and design improvements resulting from years of response experience and research. Recent improvements in skimming systems were focused on optimizing the texture and geometry of skimming surfaces to improve oil adhesion and water repellency. For example, smooth skimming surfaces have been enhanced with a specially designed material resembling a seal skin or a series of grooves to increase skimming surface area and improve recovery of oil from the water surface (Meyer et al., 2012; Miller et al., 2014). The Wendy Schmidt Oil Cleanup X CHALLENGE, initiated to address mechanical recovery challenges observed during the DWH response brought about the development of several novel skimming techniques (Meyer et al., 2012). Other advances in skimming systems include improved oil and ice processing, heating systems to facilitate recovery in cold weather conditions, and improved processing of viscous oils and emulsions. Researchers developed advanced pumping equipment to allow transfer of cold and viscous oil/water/ice mixtures (Hvidbak, 2001; Fleming and Hyde Marine, 2003).

In developing countries, where access to modern recovery equipment may be limited, booms and recovery devices have historically been made from locally available materials: nets, bamboo, floating polypropylene hawsers, foam blocks, plastic bottles and drums, etc. (Guena, 2012). In-land, sorbents and solidifiers are often used to absorb released products from the ground, prevent its further spreading, and facilitate its collection. Various types of chemical solidifiers as well as chemical and natural sorbents have been developed (Merlin and Le Guerroue, 2009). Sorbents could be used in a bulk form as fibers, powder, or granules, or in a confined form of pads, rolls, pillows, booms, or mops. They typically generate a much greater volume of waste requiring disposal than the actual volume of the product that they recover. Attention should also be paid to prevent their sinking in the water or redistribution in the environment. Collection, recovery, and disposal of contaminated sorbents is a critical and often most challenging component of response operations. Because of these reasons, use of sorbents in a loose unconsolidated form is not preferred for responses in marine environments due to additional risks that unrecovered contaminated sorbents may present to marine life. Conventional skimming systems are not designed for collection, processing, and transfer of oil-contaminated loose sorbents or solidifiers. In marine environments, sorbents can have a niche application in recovering light products when used as a sorbent boom placed inside a hard boom to facilitate its ultimate recovery and disposal.

A critical factor for an effective offshore containment and recovery operation is the availability of sufficient storage for the recovered oil/water mixture and the ability to transfer it to the shore for recycling or disposal. Even effective skimmers can recover considerable volumes of free water along with oil, especially in offshore conditions. In some cases, recovered products can contain as much as 90% water. The limited storage available on the offshore vessels may get overwhelmed resulting in a delay of recovery operations while recovered product is transferred to another vessel and taken ashore. The decanting of free recovered water in specified areas can potentially be used to optimize storage capacity and reduce downtime in recovery operations. In Canada, this method is not allowed by existing regulations, but in the United States, decanting is accepted as an integral part of response operations and is covered in area contingency plans. The MARPOL Convention also has provisions for decanting operations. If regulatory approval is granted for this procedure, free water separated from oil is drained from the bottom of a storage tank into a boomed area next to the vessel. Occasionally, this process may require the onboard chemical treatment of recovered fluids to facilitate oil and water separation. This process is always monitored and documented to prevent any additional oil from being released into the environment.

The development of special response tools and strategies for mechanical recovery in cold climate and ice conditions came about because of decades of experience. Under certain conditions, when snow, ice, or cold temperatures reduce oil spreading and allow it to remain in thick slicks and pools, mechanical recovery can be even more effective than in open water where oil can quickly spread over a very large area (Sørstrøm et al., 2010). The type and concentration of ice cover often determines the selection of a suitable containment and recovery system in cold weather conditions. A variety of techniques to contain and recover oil on—and under—solid stable ice have been developed and practiced for more than 40 years (ACS, 2015). Several types of ice-capable response vessels, that contain built-in and over-the-side recovery equipment, are used in Arctic regions (Wilkman et al., 2014). Azimuth Stern Drive (ASD) vessels have high maneuverability in ice and are very valuable for Arctic oil spill response and supporting logistics.

Conventional open water containment and recovery techniques can be used with concentrations of drift ice up to 10%. At higher ice concentrations, the opening of

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

a containment boom can be adjusted to maneuver around individual ice floes. Short sections of boom connected to an ice-strengthened skimming vessel by “outrigger arms” are used instead of long vessel-towed booms when drift ice concentrations are 10–70%. These narrower systems are easier to maneuver around ice floes and can be lifted, as needed, to avoid ice pileup inside the boom that may damage the equipment. These shorter sections of a boom direct oil toward a skimming system capable of processing oil and ice mixtures, which is built into the hull of a vessel. The ice itself acts as a containment to inhibit oil from spreading with high enough concentrations when booms cannot be used. At drift ice concentrations greater than 70%, specialized “over-the-side” skimmers can be deployed from the ice-strengthened response vessels to recover oil collected between ice floes (Potter et al., 2012). High capacity Arctic skimmers have been developed and tested with oil and ice at low temperatures (Ross, 2010; Sørstrøm et al., 2010; Meyer et al., 2014; Wilkman et al., 2014). These skimming systems were designed to process ice pieces and oil/ice mixtures. Some of them have their own propulsion systems, allowing them to maneuver between ice floes. Others may be lifted and positioned in a desired location by a crane aboard a vessel.

Decades of response experience show that mechanical recovery operations can be successfully used especially on relatively small spills in calm conditions. Mechanical recovery typically requires a greater amount of personnel, equipment and complex logistical support over a longer period of time than any other response technique. This consideration may become a critical factor when responding to spills in offshore locations or remote areas that may not be suited to host the necessary amounts of equipment and personnel for the extended period of time without negative impact on local communities and environment. Responsible use of mechanical recovery methods could be informed by a “cradle to grave” analysis evaluating potential additional environmental impacts and human exposure associated with recovery itself, the presence of a potentially large number of vessels and associated air and noise impacts; impacts associated with the transfer of oil to a disposal facility that may be located a significant distance from the response site; impacts from the recovered product disposal, possibly including incineration, recycling, or a landfill; and other activities required to support this response option.

4.2.3.3 In Situ Burning

Controlled ignition of hydrocarbon emissions to prevent their accidental ignition and reduce associated risks to human health and safety is a much-used technique. For example, a well blowout with significant volumes of gas could be ignited to mitigate a risk of accidental ignition as well as to reduce human health exposure, especially for releases with H2S, and ultimately allow safer access to the site to implement source control measures. Combustion will consume a significant portion of liquid and gaseous hydrocarbons, reducing their input into marine environments. In situ burning is a process of controlled burning of an oil slick in the field and it has been used as a response countermeasure technique for more than 60 years. Fingas (2018) provides the most recent review of this technique. The first recorded in situ burning was conducted in 1958 during a pipeline spill in the Mackenzie River, Northwest Territories (McLeod and McLeod, 1972). More recently, around 400 individual controlled burns were safely conducted during the DWH response, removing an estimated 220,000 to 310,000 barrels of oil from the Gulf of Mexico sea surface (Allen et al., 2011). Decades of research and field responses have proven that under favorable conditions, in situ burning can be a valuable response tool for removing large volumes of oil quickly, safely, and effectively with minimal environmental impact. Successful in situ burning operations eliminate the need to collect, store, transport and dispose of recovered oil as would be required in the case of mechanical recovery.

During slick combustion, liquid oil itself is not burning. The heat from an ignition source converts liquid hydrocarbons into vapors, which are then consumed by the fire. Once a small area of the slick is burning, heat from the flames will radiate to the adjacent oil, vaporize it into gas, and sustain the combustion process. The oil removal rate is a function of the oil type and its weathering degree, burning area size, slick thickness, and environmental conditions. The rule of thumb is that for fresh crude oil slick fires of more than 3 m in diameter the burning can remove oil by reducing slick thickness at a rate of about 3.5 mm/min (USCG, 2003; Buist et al., 2013a). Diesel and jet fuel fires burn at a slightly faster rate of 4 mm/min. At these rates, more than 500 bbl of oil can be eliminated in less than an hour with 500 feet of fire boom. Removal efficiency of in situ burning of crude oils has been reported as high as 98%; this means that up to 98% of collected oil can be eliminated through combustion, not that 98% percent of a total spilled volume will be burned.

The critical factor for successful burning operations is oil slick thickness. At sufficient slick thickness, oil acts as insulation from underlying cold water and maintains high temperature at a slick surface. As burning removes oil volume, a slick will eventually thin out to the point that surrounding water will cool it below the temperature required for hydrocarbon vaporization and burning will cease. Extensive laboratory and field experiments determined that minimal thickness for burning fresh crude oil on water is about 1 mm, 2–3 mm for unemulsified crude oil and diesel fuels, and about 10 mm for heavy fuel oils (USCG, 2003). Oils with water contents up to about 12.5% burn at rates similar to those of fresh oils. Stable emulsions with water contents above 25% are difficult to ignite and burn because water has to be evaporated first for the combustion process to begin (Buist et al., 2013a). If permitted by regulations, chemicals called “emulsion breakers” can sometimes be used to separate oil and water emulsions and facilitate more effective burning.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

The minimum thickness required for in situ burning is typically much greater than the thickness of a free-spreading oil slick in the field. To make oil combustible, it must be captured, thickened, and isolated from the rest of the slick with special types of booms, similar to how oil is collected for mechanical recovery. These operations require relatively calm conditions with wind speeds not exceeding 10 m/s (20 nautical miles) and wave heights lower than 3–4 feet. In a more turbulent environment, the oil may be dispersed in a top portion of the water column making it difficult to contain the oil by a boom. Safe deployment and retrieval of booms will also become a greater challenge in a more dynamic environment. Several types of fire-resistant boom designs have been developed over the years (Allen, 1999; Fingas, 2018) and tested during the DWH oil spill (Mabile, 2010). There are two main types of fire-resistant booms. One uses metallic or ceramic floats that are permanent and solid and are covered with or attached to a fire-resistant material. The other has inflatable buoyancy chambers covered with felted material and with water distribution lines that are used to continuously pump sea water to saturate and cool the material, hence reducing its direct contact with the fire.

Special safety procedures have been developed to ensure that in situ burning operations are conducted safely (USCG, 2003; API, 2015b, 2016>c, 2018a; Fingas, 2018). Booms with burning oil are always towed into the wind, so that the burn area is as far from the vessels as possible with the smoke plume dispersing away from the vessel. The burn area inside the boom can be expanded or contracted by slowing down or increasing the speed of the vessel. Should the burn require extinguishment, the vessel’s speed can be increased, allowing oil to escape under the boom into open water, or one end of the containment boom can be released to allow the oil to spread naturally. In both cases, the burning slick will spread out to thicknesses below the threshold required for sustaining combustion and fire will extinguish.

Recently, the use of oil-herding chemicals was proposed as an alternative to booms for thickening slicks for in situ burning in open and ice-covered waters. Herders are low-toxicity surface-active chemicals that can be applied in very small quantities around the perimeter of a slick to reduce surface tension of the water and allow an oil slick to contract into a smaller area and higher film thickness. Herders have existed since the 1970s, but several recent laboratory and field-scale research projects specifically evaluated their effectiveness in containing the oil and facilitating in situ burning (Buist et al., 2010, 2017; Ross and Danish Centre for Energy and the Environment, 2015; Byrne et al., 2018; Bullock et al., 2019; Tomco et al., 2022). These experiments proved that herders can effectively contract and contain oil slicks in temperate open water as well as brash and slush ice concentrations of up to 70% ice coverage and low temperatures. The burn efficiencies measured for the herded slicks were comparable to those expected from burns in conventional containment booms (Buist et al., 2010b; Kalimov et al., 2021). Herder toxicity was also evaluated: research indicated that the effects of concentrations for the tested species are several orders of magnitude greater than those expected in the field (Buist et al., 2017).

Several types of igniters are available to responders (Buist et al., 2016; Fingas, 2018). The Heli-torch was originally developed for forest-fire control, but was adopted for the use of in situ burning in the mid-1980s and was refined over the years. It works by releasing a stream of gelled fuel from a container underslung beneath a helicopter; the fuel is ignited as it leaves the device. The globules of burning gelled fuel are then dropped on a slick contained inside the boom and provide the initial ignition source to vaporize hydrocarbons and initiate the combustion process. A variety of handheld igniters that could be deployed from a vessel or a helicopter are also available (Buist et al., 2016). Most of these devices have fuses that provide sufficient delay time to assure safe deployment and ignition. In the absence of specialized ignition equipment, ad hoc devices such as weed burners, torches, and sorbent pads soaked in fuel have also been used to ignite small contained spills.

The most recent technological development combines mechanisms for application of a herder and a gelled igniter in a remotely operated surface vehicle (ROSV) built on the base design of a jet ski (Nedwed et al., 2021). The system is intended to be deployable from a ship or helicopter and operate autonomously in transit to spill locations; control is transferred to a remote operator once the slicks are located. An ROSV can travel at speeds up to 100 kph (depending on sea states), have at least an 800-km range, and at least 12 hours of operation before refueling. Once on site, the ROSV would first apply herder around the slick and then ignite the slick with a stream of gelled igniter, eliminating the need for conventional vessel-towed fire booms and exposure of personnel to hydrocarbons or burn by-products. Although this system has not yet been tested under field conditions, it holds promise for significantly improving speed and efficiency of in situ burning operations. See Figure 4.12 for a graphic summary of in situ burning tactics.

The temperatures generated during crude oil burns on water were measured to be as high as 900°C to 1200°C (Koseki, 1993; Guenette et al., 1994). Most of this heat is radiated upward and radially, while the water temperature just a few inches underneath the slick remains at ambient temperature. The flame temperatures are so high that the relative effect of ambient air temperature on the burning process is negligible whether it is +20°C or −20°C, meaning that in situ burning can be successfully conducted in cold-weather conditions. In fact, more than 40 years of research have shown that in situ burning is even more effective under cold Arctic conditions than it is in temperate climates (Buist et al., 2013a,b). This is due to the fact that burning is most effective on fresh, unemulsified oil containing light fractions, at high film thickness. At cold temperatures, evaporation slows down and oil viscosity increases, resulting in reduced spreading, smaller

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Image
FIGURE 4.12 In situ burning tactics as an oil spill response technique.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

contaminated area, and higher oil slick thickness than typically would form in warm water. The presence of ice and snow can further reduce spreading and maintain slick at higher thickness. Natural dispersion and emulsification may also be reduced due to the wave-dampening effect of ice floes and as a result, reduced mixing energy. Thicker slicks, smaller affected areas, and fresh, unemulsified oil conditions result in an extended “window of opportunity,” the time during which in situ burning could be used and can increase its effectiveness (Sørstrøm et al., 2010; Buist et al., 2013a,b).

In relatively open water with up to 10% drift ice concentrations, standard containment tactics using fire-resistant booms or herders can be used. In drift ice concentrations between 10% and 70%, when the deployment of booms becomes challenging due to potential risk of ice damage, herders could be used to corral and concentrate oil slicks. In higher ice concentrations, ice itself can act as a barrier, preventing oil spreading and concentrating it into higher film thickness. Under these conditions, oil can be burned between ice floes without the need for additional containment. Oil could also be burned on solid ice or frozen ground in pools or mixed with snow. In situ burning was shown to be effective in burning oil in concentrated drift ice off the Canadian East Coast in 1986 and the Norwegian Barents Sea in 2009 (Buist and Dickins, 1987; Sørstrøm et al., 2010), oil that surfaced in melt pools during spring time after being trapped inside the ice sheet in the winter (NORCOR Engineering and Research Ltd., 1975; Dickins and Buist, 1981; Brandvik et al., 2006), and oil mixed with small ice pieces and brash ice collected in a fire-resistant boom (Potter and Buist, 2010; Potter et al., 2012). Buist et al. (2013b) and Fingas (2018) provide the most comprehensive recent summaries of the history of in situ burning in the Arctic and cold-weather conditions.

Numerous studies evaluated composition and concentrations of emissions and residues produced as a result of in situ burning, as summarized in Sholz et al. (2004), Fingas et al. (2010), Buist et al. (2013a,b), Fingas (2018), and CTEH (2019). On average, about 85–95% of the burned oil is converted mostly into carbon dioxide and water vapor with small concentrations of nitrogen dioxide, sulfur dioxide, and other gases; 1–10% of the oil is converted to particulates (mostly soot) and the rest, 1–10% will remain on the water surface as an unburned residue. Overall, emissions from burning crude oil can be similar to those from agricultural and wildfire burns (CTEH, 2019). The black smoke made up of solid particles (soot), and liquid material (mists, fogs, sprays) may persist suspended in the air long enough to possibly be inhaled by response personnel or the public. The size of the

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

particles plays a critical role in how long they will remain in the air, how far they can be transported, and whether they can affect human lungs. Particles of 10 and 2.5 microns are usually small enough to stay suspended in the air and present inhalation risks. If inhaled at high concentrations or for a long period of time, they can cause respiratory problems. Concentration and transport of the soot particles along with emitted gases are always monitored when burning of slicks is conducted. (Refer to Section 4.2.2.4 on SMART monitoring.)

The effects of burning polycyclic aromatic hydrocarbons (PAHs) results in their complete or partial destruction or conversion into higher molecular weight (HMW) PAHs. HMW PAHs are regarded as less acutely toxic, and they are typically found in low concentrations in both soot and residue. A few of these HMW PAHs are known or suspected carcinogens and thus are monitored by chemical measurement of particulate matter around in situ burning operations. Available measurements indicate that the concentration of PAHs in emissions is typically low or barely detectable (Barnea, 1995; Fingas et al., 2001; Middlebrook et al., 2012). Because more PAHs are destroyed by in situ burning than are created, the quantity of PAHs in the smoke plume is less than in the original oil (ASTM, 2014). Human exposure to any type of burn by-products presents an inherent risk and should be carefully considered and monitored, especially for inland burns (e.g., burning oil in marshes).

Extensive studies and field tests have demonstrated that in a field application, the concentrations of smoke particulates and gases typically quickly dilute to below levels of concern (Fingas et al., 1995, 2001; Walton et al., 1995; Sholz, 2004; Buist et al. 2013a; Fingas, 2018; CTEH, 2019). Extensive research conducted by Canadian and U.S. specialists in the 1990s, involving burns with real oil, progressed the understanding of smoke components, concentrations, and downwind transport. These studies evaluated several medium-scale burns at fire test facilities in Alabama, a set of burns in Alaska (McGrattan et al., 1993, 1995), and the highly recorded Newfoundland Oil Burn Experiment known as NOBE, a large-scale burn at sea off the Canadian East Coast (Fingas et al., 1995; Fingas, 2018). The NOBE experiment offered an invaluable opportunity to conduct a full-scale burn with real oil in the field and carefully measure multiple parameters related to smoke concentration and composition (including carcinogens and PAHs), residue toxicity, and impacts on the upper water column (Fingas et al., 1995). This experiment confirmed that when in situ burning is conducted according to best practices, surface-level particulates and hazardous gas concentrations during in situ burns fall well below human health levels of concern. To ensure protection of public and responders during these operations, in situ burns are conducted at a predetermined safe distance (e.g., 3 miles) from the general public and using appropriate personal protective equipment for responders (API, 2015b, 2016c, 2018a; USCG, 2003).

Dioxins, which can have a negative impact on human health and the environment, are formed from the incomplete combustion of organic matter in the presence of chlorine. Several studies evaluated whether dioxins may present a risk to human health as a result of in situ burning. Aurell and Gullett (2010) described measurements conducted by the U.S. EPA during the DWH response and found that the concentrations of dioxins and dibenzofurans were either at background level or in the range similar to residential woodstove emissions, which is much lower than the emissions that result from burning residential waste or forest burns. Schaum et al. (2010) evaluated the risk of exposure to workers and residents and also found it to be low. Burning of oil on water is not dissimilar to burning hydrocarbons in a furnace or a car, but due to limited oxygen access it is not as efficient and produces black soot particulates that appear as black smoke. Several projects attempted to address this issue by introducing new devices aimed at improving efficiency of combustion and reducing production of soot particles (Buist, 2013a; Tuttle et al., 2017).

The unburned residue remaining after oil combustion is typically a semi-solid tarry substance that will initially float and could be collected using sorbents, but may potentially become heavier than water and sink after cooling off. Residues produced from burning in a boom towed at sea, even if allowed to sink, are expected to scatter at low concentrations at the bottom. In rare cases when a significant volume of unburned residue sinks in a relatively small area, localized suffocating of benthic habitats and fouling of fish nets are the highest concern. This was observed during the Haven spill in Italy in 1991 and during the Honam Jade spill in South Korea in 1983. There were also reports of burn residue adversely impacting the royal red shrimp (Pleoticus robustus) fishery during the DWH response.

Burn residues are less acutely toxic and less bioavailable to aquatic organisms than the original oil. This is because the combustion process eliminates the lightest, most bioavailable and most acutely toxic oil components with boiling points lower than 200°C and reduces the number of components with boiling points between 200°C and 500°C, including light and medium-weight PAHs (Garrett et al., 2000; Fritt-Rasmussen, 2012; Fingas, 2017, 2018). As a result, burn residues do not contain light hydrocarbons and have lower concentrations of total PAHs. For example, the burn residues from the NOBE field experiment had 70–75% less PAHs compared with the parent oil (Blenkinsopp et al., 1996). Because burning can remove up to 98% of the original oil volume collected in the boom, along with the light- and medium-weight PAHs, the residual volume will have a relatively higher proportion of the high molecular weight PAHs, pyrogenic components, and metals compared to the fresh oil. Although these components alone may have a chronic toxicity, in the field, they are a part of the dense residue matrix and have low aquatic bioavailability, unless directly ingested. Due to these physical and chemical changes, burn residue has low acute toxicity to indicator species in saltwater and freshwater. Studies by Daykin et al. (1994); Blenkinsopp et al. (1997), and Gulec and Holdway (1999) found little

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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or no acute toxicity of burn residues in sand dollars, oyster larvae, and inland silversides; no acute aquatic toxicity in fish (rainbow trout and three-spined stickleback) and sea urchin fertilization; no acute toxicity in amphipods; and very low sublethal toxicity (burying behavior) in marine snails. The greater risk from the residue would be the smothering of marine organisms if the burn residue was deposited to the benthic environment in high concentrations at one location.

Human health risks as well as environmental risks associated with in situ burning in the context of the risk presented by the oil spill itself are discussed in Chapter 6. The impact of a temporary reduction in air quality from burning and any potential impacts of oil residue should be weighed against the impact of an untreated oil in the environment. As much as 30–50% of the spilled volume may evaporate naturally, so a reduction in air quality could be expected regardless of the response method involved. Responders involved in in situ burning work under robust safety plans that address the risks and exposures associated with the response (API, 2015b, 2016c, 2018a; USCG, 2003). Exposure to the general public is minimized by conducting burns at a considerable distance from populated areas (e.g., 3 miles in most U.S. regions) and only under favorable conditions that allow dilution of the smoke plume below levels of concern. In situ burning operations in the field are always accompanied by a monitoring program (see Section 4.2.2.5) involving visual observations, measurements of gases and particulate composition and concentration, and air sampling. Modeling can also be used to predict concentration of particulates in the plume and potential trajectory of the plume and particulates (Walton et al., 2003). Additional observations are conducted to estimate the volume of oil that was eliminated through in situ burning (Mabile, 2013).

4.2.3.4 Dispersants

Several recent publications provide a more detailed overview of dispersant science as well as impacts of dispersants and dispersed oil on the environment: A publication by the National Academies of Sciences, Engineering, and Medicine, The Use of Dispersants in Marine Oil Spill Response (2020); The Canadian Science Advisory Secretariat report State of Knowledge of Chemical Dispersants for Canadian Marine Oil Spills (DFO, 2021); and the GAO-22-104153 report Offshore Oil Spills: Additional Information Is Needed to Better Understand the Environmental Tradeoffs of Using Chemical Dispersants (GAO, 2021). This section focuses on operational aspects of dispersant use in marine environments as one of the components of the response toolbox.

Surface Dispersants

The rapidly changing offshore environment require access to all appropriate response options to ensure maximum response effectiveness and environmental protection for an effective response. Response techniques such as mechanical recovery and in situ burning using fire-resistant booms require deployment of a large number of field personnel and on-water equipment and are challenged by the need to collect and concentrate spread-out patchy oil slicks. Though they can be effective in responding to small spills in calm waters relatively close to equipment stockpiles, they may not be as effective in recovering large offshore spills in remote areas or in high wind and sea conditions (Schmidt Etkin and Nedwed, 2021). In these situations, an aerial application of dispersants may be a critical response tool. Dispersant planes are able to arrive at a spill site quickly, treat larger volumes of oil, and operate in higher sea and wind conditions with limited risk and exposure to a smaller number of personnel involved than other response techniques. In a surface application, dispersants can also be sprayed from helicopters and from vessels either using fire cannons equipped with spray nozzles or specially designed application equipment (see Figure 4.13).

Dispersion of oil is a natural process facilitated by wave action, which breaks the oil into small droplets and dissipates the droplets into the water column (Delvigne and Sweeney, 1988; NASEM, 2020; see Section 5.3.1.3). The properties of the oil combined with extent of wave energy at the surface determine the effectiveness of this process. In most cases, lower viscosity oils are more inclined to natural dispersion than those with higher viscosity. Also, higher wave energy generates greater natural dispersion. Oil droplets of less than 100 microns in diameter (roughly the diameter of a human hair) generally tend to stay suspended in the water column, dilute, and eventually biodegrade; larger droplets are more likely to float back to the surface and re-coalesce into a slick. A portion of any spill in the marine environment is expected to disperse naturally. Several spills in rough sea conditions were completely dispersed by the natural wave action; an example is the North Cape spill (Michel et al., 1997).

Chemical dispersants are mixtures specifically designed to enhance natural dispersion of oil in marine environments. Dispersants typically consist of surface-active agents (surfactants) and a solvent (NASEM, 2020). The surfactant molecules consist of two parts: an oleophilic part that tends to stay in oil and a hydrophilic part that tends to stay in water. Upon contact with oil, these molecules orient themselves at an oil-water interface and reduce the interfacial tension, making it easier for waves or other turbulence to create small oil droplets and dissipate them in the water column (Clayton et al., 1993). Monomolecular surfactant “coating” around the droplets also minimizes re-coalescence and general stickiness of the droplets. The solvent reduces the viscosity of the surfactant, allowing it to be sprayed from the plane in the form of small droplets of about 600 to 800 microns in diameter and facilitates penetration of the surfactant into oil. Dispersing an oil slick into water as droplets creates greater surface area at the oil-water interface, thus increasing availability for natural biodegradation (NASEM, 2020; Pequin et al., 2022) (see Section 5.2.8.3).

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Image
FIGURE 4.13 Dispersant application methods and monitoring techniques.
NOTE: S.M.A.R.T. = Self-Monitoring, Analysis and Reporting Technology System.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

The first application of dispersant-like chemicals in an oil spill response took place in 1967 during the Torrey Canyon oil spill in the United Kingdom (see Section 6.5.3.3). The chemicals used to disperse the oil were industrial degreasers, which were not intended for use in marine environments. Since then, several generations of modern dispersants have been developed using low-toxicity ingredients also used in household products, food, and cosmetics (Hemmer et al., 2011; Word et al., 2015; NASEM, 2020). Although the exact composition of most commercial chemical dispersants is proprietary, the composition of Corexit EC9500A was disclosed during the DWH spill. It contains the surfactants DOSS, Tween 80, Tween 85, and Span 90 as well as glycols and dipropylene glycol n-butyl ether (DGBE) in a hydrotreated light petroleum distillate (Parker et al., 2014; Fingas, 2017). All these ingredients are approved by the U.S. Food and Drug Administration and have other household uses. For example, the anionic surfactant DOSS (dioctyl sulfosuccinate sodium salt; sodium dioctyl sulfosuccinate) is a common ingredient used in a variety of applications such as a wetting and flavoring agent in food, a cosmetics ingredient, and an over-the-counter laxative. Dickey and Dickhoff (2011) provide a detailed overview of Corexit ingredients, their uses, and their environmental toxicity. Recently, researchers explored the use of biosurfactants and natural surfactants as alternatives to chemical dispersants (Quigg et al., 2021a; Pequin et al., 2022). While showing some promise at a laboratory scale, further research and development are needed to optimize these concepts and formulations for various spill scenarios and demonstrate their feasibility for field use, as well as to evaluate their industrial-scale production and distribution.

In 1996, 445 tons of modern-formulation dispersants were used nearshore during the Sea Empress oil spill in an effort to protect sensitive coastal resources from the impacts of drifting oil; this prevented at least 36,000 tons of oil from washing ashore (Harris, 1997). During the 1979 Ixtoc 1 spill in the Bay of Campeche, Mexico, response efforts over a five-month period applied approximately 9,000 tons of dispersants (Jernelöv and Lindén, 1981). When the Montara wellhead blew out in 2009 in Western Australia, 48,000 gallons of a combination of seven different dispersants were used (NASEM, 2020). During the DWH incident approximately 53,000 tons of dispersants were applied through a variety of deployment resources, including aerial, vessel, and subsea methods. Prior to the DWH incident, between 1968 and 2007, dispersants were (reportedly) operationally used globally 213 times (Steen and Findlay, 2008). Over the past 40 years, dispersants were used in the United States 27 times (Helton, 2021).

Chemical dispersants are most effective when applied during or quickly after a spill or sub-sea release incident. Natural processes such as dilution, weathering, and emulsification of the oil can quickly reduce the effectiveness of surface dispersants, creating a limited “window of opportunity”

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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(the time window during which application of surface dispersants can be successful). The effectiveness of surface dispersants is influenced by the efficiency of the employment process (encounter rate), properties of the slick at the time of application (e.g., viscosity, pour point, slick thickness), and the sea conditions (e.g., wave energy).

Encounter Rate

The encounter rate for surface dispersant deployment is determined by the speed of the delivery vehicle, the amount of dispersant that it can apply, and the width of the spray pattern. A Boeing 727 dispersant aircraft can travel at speeds of more than 500 miles/hour compared to a transit speed for a response vessel of 8 miles/hour. A Boeing 727 can arrive at a spill site quickly, before an oil slick spreads out over a large area or breaks into small patches. Another dispersant plane, a C-130A with an internal spray system can treat around 7,000 bbl of oil with a dispersant-to-oil ratio of 1:20 in a 12-hour day, compared to the 1,000 bbl that could be recovered by a large oil spill response vessel even under optimal conditions (API, 2015a). The encounter rate of aerial dispersants is the highest on continuous slicks. Once oil spreads out, thins out, and breaks into smaller slicks (patches) aerial application may have reduced efficiency.

Slick Properties

Not all oils are suitable for dispersion. Properties that determine oil dispersibility include chemical composition, density, viscosity, pour point, and the degree of weathering. As discussed in Chapter 2, very volatile hydrocarbons (Group I) evaporate rapidly and are typically allowed to do so. Very heavy products (Group V) that have density higher than water are also not suitable for dispersion. An oil cooled below its pour point (the temperature at which oil remains liquid) may become very viscous and lose its dispersibility. Dispersants can be used on slicks much thinner than those that could be collected for mechanical and in situ burning operations (typically higher than 0.1 mm), but are typically not applied on very thin sheens of less than 0.05 mm, as dispersant droplets could penetrate through the sheen and into the water column without interaction with the oil. Surface dispersants are most suitable for liquid hydrocarbons that form dark/black slicks on the water surface and are not expected to attenuate naturally. Dispersants are most effective on fresh oils. As a result of weathering processes (see Chapter 5), oil viscosity increases over time due to evaporation of lighter fractions. In addition, many crudes and some refined products can form stable, difficult-to-disperse emulsions when, over time, wave action mixes them with water. The use of dispersants can disrupt or prevent formation of stable water-in-oil emulsions and, in some cases, even undo already formed emulsions. The time window during which surface dispersants are effective can be as short as one to three days, after which the oil could become too viscous or emulsified. The type of oil, as well as freshness, affects its dispersability, newly spilled light to medium crude oils are considered readily dispersible whereas highly viscous oils are not. In the late 1970s it was assumed that dispersants were not effective on oils with a viscosity greater than 2,000 cP, which is similar to honey at room temperature (Martinelli and Cormack, 1979). Studies that are more recent have shown modern dispersants are more effective at dispersing weathered and emulsified oils, and are effective on oils with a viscosity as high as 20,000 cP, which is similar to chocolate syrup at room temperature (Lewis et al., 1995; Strøm-Kristiansen et al., 1997; Lessard and DeMarco, 2000; Belore et al., 2008; Nedwed et al., 2008). As a rule of thumb, oils with a viscosity of up to 10,000 centipoises are considered potentially dispersible (Daling and Strøm, 1999), but whether or not they could actually be dispersed at sea, depends on the sea conditions.

Sea Conditions

Dispersants can be used over a wider range of sea conditions than other response options, and this is the only response technique that can be used in high waves and winds. An important factor for surface dispersant application is the sea state, it affects both the mixing energy available for breaking slicks into small droplets and the effectiveness of oil plume dilution in the water column. At low mixing energies, dispersion may be ineffective and any droplets that were dispersed may resurface back to the slick. Oil slick can be treated with dispersants in calm conditions so that it can disperse when wave energy increases in the following days. If wave energy is too high, oil may be dispersed naturally in the water column and not be available for treatment. Generally the upper limits for spraying dispersants from aircraft are gale force winds (speeds > 35 knots [18 m/s]) and wave heights of 5 meters, there are instances where dispersants have been applied from aircraft in winds greater than 50 knots (ESGOSS, 1994; IPIECA, 2015). High wind and wave conditions affect not only dispersant application efficiency, but also the safety of surface spraying operations.

Another important limitation for surface dispersant application is visibility. Sufficient visibility to accurately track the oil slick (e.g., cloud ceiling of 1,000 feet and daylight) are necessary to perform aerial dispersant applications. Spraying operations from the vessel could potentially proceed at night with support from specialized remote sensing equipment. During an actual event, the operational use of dispersant may have to be preceded by a small-scale field test to ensure that the specific dispersant will work on the specific oil under the specific weather and field conditions.

While the dispersants efficiency measurements from actual spill responses are limited, measurements obtained from the field scale tests and experiments in large test tanks report high effectiveness of dispersant applications (Belore et al., 2008, 2009; Ross, 2011; NASEM, 2020). In contrast,

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

standard laboratory tests used to evaluate effectiveness of dispersants for the purpose of regulatory approvals typically report dispersion efficiency in the range of 40–60% (EPA, n.d.a). This is because simulating dispersion under actual field conditions have not been the objective of standard laboratory tests. Rather, they were designed to screen candidate dispersants and are intentionally conducted at low mixing energy to allow better differentiation between candidate dispersants. Assessing the effectiveness of oil dispersants under more realistic sea state conditions experiments should be conducted in large test tanks—and even then there are inherent limitations which may affect dispersant performance (Nedwed and Coolbaugh, 2008). When dispersion tests have been conducted in large test tanks results exceeded those observed in small-scale tests and demonstrated high effectiveness of dispersants. For example, Corexit 9500 and Corexit 9527 were 85–99% effective in dispersing both fresh and weathered Alaskan oils in a test tank even when tested at cold temperatures (Belore et al., 2009). Test tank experiments also showed good dispersibility of viscous oils compared to bench-scale experiments (Belore et al., 2008). Figure 4.14 illustrates the effect of oil type and viscosity (shown in parentheses), as well as test method, on the results of the effectiveness tests conducted by Ross in 2011. Tested oils included Alaska North Slope (ANS), Harmony, and PXP-02 (Irene commingled crude), as well as intermediate fuel oils (IFOs). Ohmsett is a very large outdoor test tank that can generate turbulence comparable to that in marine environments. Other test methods are bench scale with various levels of mixing/turbulence. The Exxon Dispersant Effectiveness Test (EXDET) was designed to generate relatively higher turbulence to better represent ocean turbulence than used in the swirling flask test or Warren Spring Laboratory used for screening of dispersants for regulatory certification purposes. The baffled flask test is a modification of the swirling flask test that allows testing at higher turbulence, but is still not directly translatable to field conditions. Higher viscosity oils are generally less dispersible, but even they could be dispersed in the field, test tanks, or bench scale tests with sufficient level of turbulence compared to the bench scale tests with limited mixing. The direct use of the dispersant efficiency values generated for the purpose of regulatory certification in low-turbulence conditions is not appropriate for the prediction of dispersant efficiency in the field and operational decision-making. This may prevent the use of dispersants that could have been effective under field conditions, which most of the time have higher levels of natural mixing and dilution potential than those simulated in the small-scale laboratory tests. A pilot spray test is often conducted in the field to confirm the effectiveness of dispersant use under specific field conditions.

Image
FIGURE 4.14 Comparison of dispersants efficiency estimates as a function of oil viscosity (highlighted in parentheses) and the type of the test.
NOTE: cP = centipoise.
SOURCE: Adapted from SL Ross (2011).
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Several studies have shown that the dispersability of many oils have not been significantly reduced by cold temperatures (Brown and Goodman, 1996; Owens and Belore, 2004; Lewis and Daling, 2007; Sørstrøm et al., 2010; Lewis, 2013; Lewis and Prince, 2018), and most oils remain dispersible until they are cooled below their pour point (Daling et al., 1990, Brandvik et al., 1995; Nedwed et al., 2006). Although cold temperature can increase oil viscosity, this change is usually not as drastic as the viscosity increase resulting from oil evaporation and emulsification. These weathering processes can proceed quickly in warm climates, potentially limiting the window of opportunity for surface oil dispersion to one to three days. In contrast, Arctic and cold-weather conditions can increase the period of effectiveness for dispersant use by reducing oil weathering (Brandvik et al., 2010; NRC, 2014). An oil slick in cold weather conditions will have lower spreading and evaporation rates, especially if contained between ice floes. Under these conditions, the oil may remain fresh and dispersible from days to weeks. Ice-covered marine environments typically have low mixing energy conditions due to absence of breaking waves, although some studies found that the motion and contact between broken ice floes under certain conditions could generate surface turbulence sufficient for dispersion (Owens and Belore, 2004; Faksness et al., 2017). The icebreaker-facilitated dispersion concept was introduced to overcome the wave-dampening effect of ice and provide the necessary turbulence. This technique uses the mixing energy from the propeller of an ice breaker or support boats to disperse dispersant-treated oil (Spring et al., 2006; Nedwed et al., 2007; Daling et al., 2010). A special hydraulic arm operating from the side of the vessel was developed for targeted application of dispersants between ice floes. A 2009 field experiment in the Arctic demonstrated the effectiveness of this technique on oil that was weathered between ice for 6 days (Sørstrøm, 2009). Experiments have also shown that oil can remain dispersible during spring melt after being encapsulated into ice for as long as 3 months (Nedwed et al., 2017). Although most commercial dispersants were formulated for use in marine environments and have reduced effectiveness in waters with lower salinities, several dispersant types are available for use in fresh waters.

Under offshore conditions, dispersed oil is expected to dilute in the top portion of the water column and be carried away and dissipated by the currents. Because currents typically run parallel to the shore, oil dispersed offshore is not expected to arrive at the shore, as surface slicks driven by the winds often do. Dispersants are typically applied in marine environments at water depths greater than 10 meters and 3 nautical miles away from a shoreline. This is to allow sufficient dilution of the dispersed plume and reduce potential exposure to aquatic organisms. Application of dispersants in shallow waters can be suitable under some circumstances but should be evaluated on a case-by-case basis to examine potential benefits, such as protecting sensitive or economically important nearshore or shore line areas versus potential impacts in the water column. Effective dispersant use increases concentration of oil in the water column, but because slicks are dispersed into the water immediately underneath, oil is typically dispersed into the area already contaminated with hydrocarbons. This volume will experience the highest initial loading of dispersed oil before ultimate plume dilution. Dispersants are typically not used in shallow waters with limited water circulation and dilution potential or in waters with high sediment load, typically found close to the shore and in estuaries. Chemically or naturally dispersed oil in waters with high turbidity and organic content could potentially result in formation of marine snow. Brakstad et al. (2018c) conducted a critical review of marine snow literature in the context of oil spills and dispersant treatment, but concluded that the exact contribution of dispersant to the formation of marine oil snow events during the DWH oil spill could not be determine from available published laboratory studies, as these studies were performed at very high oil concentrations and not representative of the rapid dilution in the open ocean. A more detailed discussion can be found in NASEM (2020) and Section 5.3.2.2.

Experiments and field observations have shown that initial dilution of dispersed oil in the field is rapid with maximum measured dispersed oil concentrations being 10–50 mg/L (NASEM, 2020). Trudel et al. (2009) showed that, even in closed wave tanks, concentrations of dispersed oil are rarely higher than 100 mg/L. This initial concentration is reduced through dilution and advection to 1 to 2 mg/L in less than 2 hours (Cormack and Nichols, 1977; McAuliffe et al., 1980, 1981; Lunel, 1994; Daling and Indrebo, 1996; Strøm-Kristiansen et al., 1997; NASEM, 2020). With time, dispersed oil plumes continue to dilute and offshore concentrations of dispersed oil are estimated to fall below a threshold for acute impacts for aquatic organisms in less than a day (Cormack and Nichols, 1977; McAuliffe et al., 1980; French-McCay and Payne, 2001; French-McCay et al., 2006; Judson et al., 2010; BenKinney et al., 2011; Coelho et al., 2011; Hemmer et al., 2011; Bejarano et al., 2013). This explains why during the DWH response, only 33 samples had TPH concentration higher than 10 ppb among 2,779 individual samples collected in that area (Lee et al., 2011b, 2013). An extensive federal and state monitoring program initiated after the DWH oil spill to address public concerns about the consumption of seafood tainted from the oil, dispersants, and dispersed oil found that dispersed oil levels were well below levels of concern (LOC) for human health risk (FDA, 2011; Gohlke et al., 2011; Ylitalo et al., 2012). Additional research into the topic of seafood safety has identified improvement opportunities for future monitoring programs: for example, the need to include alkylated polycyclic aromatic hydrocarbons into human health assessment for contaminated seafood (see Farrington [2020] and Chapter 6 for more details).

Dispersants alone are also present in low concentrations in the water. The typical dispersant-to-oil ratio for surface

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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application of modern dispersants is generally around 1:20, and a standard aerial application rate is 5 g/acre (47 l/ha). If this volume of dispersant was applied to water, the resulting initial concentration of dispersant in the top meter of seawater would be around 5–13 ppm and would dilute to less than 1 ppm within minutes to hours (Lewis and Prince, 2018; NASEM, 2020), which is well below the toxicity threshold for most aquatic species (NASEM, 2020). After application, dispersants are subjected to dilution and degradation processes, including biodegradation and photodegradation at the surface. The early literature on surfactants, based on laboratory experiments, provided evidence both for and against inhibition of biodegradation of dispersed oils, but some of these studies used unrealistic incubation conditions including excessive concentrations and dispersant:oil ratios (Prince and Butler, 2014). More recent literature generally has demonstrated that dispersants do not inhibit oil biodegradation (Prince et al., 2013) but rather promote biodegradation (e.g., Bælum et al., 2012; Sun et al., 2019), although contradictory results are still reported from laboratory studies (e.g., Kleindienst et al., 2015; Langenhoff et al., 2020); diverging results are likely due to differences in experimental design (NASEM, 2020). Laboratory experiments measuring Corexit EC9500A loss have shown that the surfactant compounds DOSS, Tween 80, and Tween 85 and the petroleum distillates biodegrade on the order of days (Garcia et al., 2009; Campo et al., 2013; Brakstad et al., 2018b; NASEM, 2020). Although the general consensus seems to be that dispersant constituents are biodegradable, DOSS biodegradation may be delayed in the presence of oil and its metabolite ethylhexyl sulfosuccinate (EHSS) may transiently accumulate (Gofstein et al., 2020). It appears that dispersant components generally do not persist at high concentrations in marine waters, especially at the surface where photo-oxidation can occur (Ward et al., 2018a), but may persist when sequestered in sediments (White et al., 2014).

Prince (2015) reviewed the literature and proposed that the overall environmental benefits of using oil spill dispersants likely outweigh any potential negative environmental impacts, while listing numerous questions that remain regarding dispersant use. When effectively applied, dispersant use can reduce the potential of the public to come in contact with oil by preventing oil from coming ashore. On-scene health hazard evaluations performed by the National Institute for Occupational Safety and Health (NIOSH) found that standard personal protective equipment with exposure monitoring (if deemed necessary) was adequate to protect oil spill responders including during dispersants operations (NIOSH, 2010; King and Gibbins, 2011). Dispersants also reduce the potential of workers to be exposed to oil and oil fumes while conducting clean up and recovery efforts at sea or on the shoreline. Some researchers have evaluated whether application of dispersants may increase aerosolization of oil into atmosphere (Afshar-Mohajer et al., 2020), although further studies are needed to translate these laboratory findings into field conditions and integrate them into larger scale dispersion and exposure models. The comparison of emissions for the total time that untreated oil slick is present at the water surface versus emissions from the limited duration that a treated slick is present on the surface before it disperses into water column will provide valuable information for this comparison. A more detailed discussion on the effects of dispersants and dispersed and undispersed oil on human health can be found in NASEM (2020).

Dispersant application in the field is typically accompanied by a variety of dedicated monitoring programs (e.g., SMART; see Section 4.2.2.4) as well as more comprehensive water column and air quality sampling and monitoring activities. It is critical to collect field data on the actual dispersant effectiveness, water column concentrations, and transport to validate assumptions of the Net Environmental Benefit Analysis (see Section 4.2.5) and better assess environmental and socio-economic impacts of oil and dispersed oil.

Point-Source and Subsea Dispersant Injection

When an oil spill occurs at a localized source and involves a continuous release, chemical dispersants may also be applied directly at the spill source (see Figure 4.15). For cases

Image
FIGURE 4.15 Illustration of the effect of use of subsea dispersants on the fate of released oil.
SOURCE: IPIECA.
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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involving an accidental oil well blowout or a leak from a disabled pipeline near the sea floor, this type of dispersant application is termed subsea dispersant injection (SSDI). This technique is not used exclusively in deep waters, and could potentially be applied to shallow or even surface releases. In this case, it would be considered a “point-source” injection aiming to premix dispersants into uncontrolled release so that oil can later be dispersed by waves at a sea surface.

SSDI was first used as a major response option during the DWH oil spill. As with all dispersant applications, it is only used when mechanical collection and recovery are not feasible to collect all the released oil and the oil is already entering the marine environment. The purpose of SSDI is to enhance natural dispersion of the released oil into the water column and, especially for subsea spills, to limit the amount of liquid hydrocarbons and volatile compounds reaching the sea surface where they may pose a hazard to humans, marine mammals, birds, and other marine life.

SSDI is not always an appropriate response technique. For example, a blowout of a condensate may naturally disperse in the water column as well as disperse and evaporate once it reaches the water surface, not requiring additional intervention. Under some circumstances, it may be more advantageous to let hydrocarbons evaporate into atmosphere than enhance their dispersion into water column. SSDI could potentially be considered for blowouts that result in a formation of a large surface slick threatening environmental resources if the spill cannot be addressed by other response measures, or to protect source control responders from harmful hydrocarbon vapors. The potential effectiveness of SSDI, its additional impacts, logistical feasibility, complexity of the regulatory approvals, and stakeholders’ concerns should all be carefully evaluated before the decision to proceed is made.

Subsea dispersant injection typically involves several steps:

  • A vessel with specialized dispersant injection equipment and stockpiles of dispersants arrives at the site.
  • An ROV positions the nozzle of a flexible line connected to the vessel as close to the release point as possible to allow direct injection of dispersant into the oil stream. Alternatively, dispersant could be injected through special ports on a well-capping structure.
  • Dispersant is pumped at a controlled rate from the deck of the vessel.
  • Dispersion efficiency is monitored and injection rate is adjusted accordingly.

One of the primary reasons for SSDI injection is to reduce the volume of oil and gas surfacing near the release site to create less hazardous working conditions for source control vessels working on closing the well and stopping the release of hydrocarbons into the environment. Another reason to consider SSDI is that lower dispersant volumes may be required, due to lower dispersant-to-oil ratios (DORs) for equivalent effectiveness, and more oil may be treated than by surface dispersant spraying. Several studies have evaluated the effectiveness of SSDI (Brandvik et al., 2017; Gros et al., 2017; Zhao et al., 2021; see Chapter 5). Zhao et al. (2021) analyzed 91,566 volatile organic compound (VOC) measurements from the DWH spill collected near the well site and concluded with statistical confidence that SSDI reduced airborne VOC concentrations at the well site and enhanced the safety and health conditions of the responders. Measured VOC concentrations were lower during subsea dispersant use, and incidents of peak concentrations exceeding 50 ppm VOC that could have been of immediate concern to worker health were reduced by a factor of ~6 to 19 when dispersants were delivered at the intended rate. A study by Gros et al. (2017) also discussed the effectiveness of SSDI in dispersing oil at depth and the resulting changes in hydrocarbon concentrations at the water surface. Those authors reported that dispersant injection decreased the size of the droplets, which increased dissolution of hydrocarbons in the water column. Higher dissolution of light hydrocarbons in the water resulted in a 2,000-fold decrease in emissions of benzene at the surface, which lowered health risks for source control workers. Section 5.3.3.5 includes a more detailed discussion on the effect of subsea dispersants on formation and fate of oil droplets as well as its overall effectiveness. As with other response options, SSDI effectiveness in the field depends on many factors and it is not anticipated to be 100% effective, yet, as discussed in Section 5.3.3.5, even modest changes in oil droplet sizes could potentially result in considerable changes in their behavior and corresponding transport and impacts of the spill at large.

The advantages of SSDI, as compared to application of dispersants at a sea surface, include (IPIECA and IOGP, 2015):

  • SSDI is suitable for almost any weather condition and around-the-clock operations. Other response techniques often have to cease during the night and are much more sensitive to limitations imposed by environmental conditions.
  • The degree of control over the dispersant application process is higher when dispersants are injected at one manageable location directly into oil rather than sprayed from planes on patchy weathered surface slicks.
  • Large oil volumes can be treated immediately at the source. The fresh nature of the oil combined with potentially high mixing and turbulence at the release point create advantageous conditions for effective dispersion.
  • SSDI can reduce the amount of oil reaching the surface, forming slicks, affecting marine mammals and birds, or drifting toward sensitive areas and shorelines where high densities of organisms at sensitive life stages may be present.
  • SSDI can reduce the need for other response measures including surface recovery, in situ burning, and surface
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
  • dispersant operations, which also reduces the possibility of exposure or accidents during these operations.
  • SSDI can reduce/eliminate challenges associated with handling, storage, and disposal of large volumes of waste that could otherwise be generated by on-water mechanical recovery and shoreline clean-up operations.
  • SSDI can reduce the amount of oil exposed to sunlight that may potentially increase their overall toxicity and impacts.
  • SSDI requires a lower dispersant-to-oil ratio compared to surface spraying operations (1:100 subsea versus 1:20 at the surface).
  • Larger water volume is available for dispersed oil dilution compared to surface application.

As with all response tools, the benefits of SSDI must be evaluated against potential operational challenges and additional environmental impacts. Subsea injection of dispersant in deep waters is a complex procedure requiring specialized injection and monitoring equipment. In a high flow rate oil and gas blowout, a portion of released oil may naturally disperse and dissolve in the water column. SSDI further increases the concentration of hydrocarbons in the water and hence potential exposure to marine organisms in certain areas (see Chapters 5 and 6 for more details). During the DWH spill, higher concentrations of hydrocarbons were observed in subsea intrusion layers, such as the deep plume between 1200 and 900 m water depth. Gros et al. (2017) estimate that on June 8, 2010, 1.5 times as much dissolved petroleum fluids by mass entered the subsea intrusion than would have occurred without SSDI. It should be noted, though, that concentrations of hydrocarbons in this plume were mostly at the ppm level. Hydrocarbon concentrations were consistently well below 5 ppm measured at about 1 km (0.6 mi) from the wellhead at 1,200 m depth (3,937 ft) (BenKinney et al., 2011; Coelho et al., 2011). About 84% of more than 20,000 water column samples had oil concentrations below 1 ppb, even though sampling was focused on locations where hydrocarbon concentrations were expected (Wade et al., 2011, 2016).

Dissolved and dispersed hydrocarbons are in a suitable form to be degraded by in situ bacteria, and several studies have documented the effectiveness of biodegradation in the DWH subsea plume (Valentine et al., 2010; Kessler et al., 2011; Hazen et al., 2016). Depending on the location of a spill globally, this may have important implications for oxygen concentration in the deep ocean as aerobic bacteria consume dissolved oxygen along with hydrocarbons. Indeed, the subsea plume associated with the DWH oil spill could be identified by dissolved oxygen anomalies in the CTD profiles collected during the spill. For this region of the Gulf of Mexico, oxygen concentration remained well above critical levels. However, at other locations around the globe, such as offshore Western Africa, where background oxygen concentrations are already low, dissolved oxygen may fall to hypoxic levels as the dissolved material from a subsea blowout is degraded.

The effectiveness and efficiency of SSDI application in the field will vary and depends the number of factors such as oil properties, the application method, the release conditions, and others. In situ monitoring is needed to evaluate the effectiveness of SSDI and confirm its applicability. Several documents were developed by both governmental agencies and industry to guide monitoring of SSDI (NRT, 2013; API, 2020; EPA, 2021; NRT, 2021). The purpose of operational SSDI sampling and monitoring described in detail by API (2020) is to:

  • Determine dispersant efficacy.
  • Characterize the dissolved oxygen and oil droplet sizes for subsea, or near surface, dispersed oil plumes including background samples.
  • Assess potential ecological effects as they relate to operational response decision-making.

Operational SSDI monitoring is organized in three phases of increasing complexity:

  • Phase 1: Confirmation of dispersant effectiveness near the discharge point and reduction in surfacing VOCs (e.g., improvement of air quality).
  • Phase 2: Characterization of oil droplet size near plume and dispersed oil concentrations at depths in water column.
  • Phase 3: Detailed chemical characterization of water samples.

The National Response Team (NRT) 2013 Monitoring Guide describes a comparable program encompassing:

  • Site characterization;
  • Source oil sampling;
  • Water sampling and monitoring; and
  • Sediment sampling and monitoring.

Although the API guide is focused on operational sampling and monitoring that can assist with real-time decision-making, the NRT recommends more detailed analysis of potential environmental impacts. Whether as a part of an SSDI monitoring program, or as a separate program, additional sampling and monitoring activities are always conducted to assess environmental impact as it relates to NRDA.

In 2021, the U.S. EPA published an updated rule, Dispersant Monitoring Provisions Under Subpart J of the National Contingency Plan, addressing dispersant use in response to major oil releases and other specific uncommon dispersant use situations in the navigable waters of the United States and their coastlines (EPA, n.d.).

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

The amendments establish dispersant monitoring requirements for the following scenarios:

  • Use of dispersants in subsurface settings;
  • Surface use of dispersant over prolonged periods, specifically in excess of 96 hours after initial application; and
  • Surface dispersant use in response to oil discharges greater than 100,000 U.S. gallons in a 24-hour period.

The monitoring elements in the final rule include:

  • Source Characterization and Information on Dispersant Application—Flow rate or volume of oil discharged, type of dispersant, dispersant-to-oil ratio, application rates, and total amount of dispersant needed.
  • Water Column Sampling—In situ water column samples of background, baseline, and dispersed oil plume with recorded oil droplet size distribution, fluorometry and fluorescence, total petroleum hydrocarbons, dissolved oxygen (subsurface only), methane (subsurface only), heavy metals, turbidity, water temperature, pH, and conductivity.
  • Oil Distribution Analysis—Description of dispersant efficiency and oil distribution.
  • Ecological Characterization—Description of potential ecological receptors and habitats, and their accompanying exposure pathways.
  • Immediate and Daily Reporting—Immediate reports for alterations to specified application plan, and daily reports of water sampling and data analyses to the On-Scene Coordinator and the Regional Response Team.
Subsea Mechanical Dispersion

An alternative dispersion method was recently proposed (Brandvik et al., 2021) for use under some circumstances when dispersion of a subsea blowout is desirable, but not achievable, either because chemical dispersants are not allowed or not available, or if a blowout does not have sufficient turbulence to break the plume into small droplets. Researchers tested various methods to facilitate the formation of small oil droplets by introducing mechanical mixing within the rising oil plume. After evaluating rotating mixing blades, ultrasonic cavitation, and high-pressure water jetting they concluded that creation of additional turbulence by introducing a powerful jet of water across the plume is the most promising technique, especially because it can be delivered using the equipment typically available at offshore facilities. Although this technique still has to be verified under field conditions and different blowout scenarios, it may become a viable response option in some situations. Since subsea mechanical dispersion relies on the power of a water jet to generate smaller droplets by cutting across the blowout, it may have limitations during high-volume blowouts and with certain oil types. In some scenarios, this technique could potentially facilitate subsea blowout dispersion when conventional SSDI is not possible or to increase the effectiveness of conventional SSDI, if needed.

4.2.3.5 Summary of Offshore Response Techniques

Earlier sections described a number of techniques that are available to respond to offshore oil spills. No technique is 100% effective under every response scenario, and there are advantages, challenges, and optimal conditions for the use of each technique. The conditions specific to each spill inform response decision-making so that the optimal combination of response techniques can be selected that will result in maximum protection of sensitive resources. Table 4.2 summarizes benefits, challenges, and potential additional impacts for different on-water response techniques.

4.2.3.6 Submerged and Sunken Oil Response

Spilled oil and hydrocarbon products may become submerged in the water column or sink to the bottom either if their initial or weathered density exceeds the density of seawater or if they form heavy agglomerate after mixing with suspended sediments (refer to Chapter 5 for more details). The API Technical Report and Operational Guide on Sunken Oil Detection and Recovery (2016a,b) provide a recent overview of recovery methods that could be used in such situations, along with their advantages and limitations. The effectiveness of these techniques will be strongly influenced by the response conditions (e.g., depth, visibility, sediment load, accessibility, presence and absence of ice, current speed, etc.) as well as product properties and behavior (e.g., sunken to the bottom or floating in the water column, in a shape of large mats or small aggregates, solid or liquid, concentration, areal distribution, etc.). Large concentrated oil mats are typically easier to recover than scattered small aggregates. Depending on the conditions, this could be accomplished by a variety of techniques: divers with pumps or vacuums, heavy machinery such as a dredge or an excavator, nets, trawls, and sorbents can be used. Table 4.3 summarizes applicability of available recovery techniques under various conditions.

4.2.4 Shoreline Protection and Cleanup

One of the results of discharges of oil into the environment is that it may eventually strand and, depending on the location, may affect open-water facing beaches and shores, rocky or vegetated shorelines, tidal flats, or manmade structures, such as rip-rap, jetties, or bulkheads. Appendix G, as well as Section 5.3.4.1, describe various shoreline types and potential oil fate and behavior in these unique environments. Various response methodologies have been developed to protect, clean up, and mitigate the detrimental effects of such oiling events. These strategies are often specific to shoreline types, environmental conditions, oil types, and even stakeholder

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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TABLE 4.2 A Summary of On-Water Response Options

Benefits Challenges Potential Impacts
Monitored Natural Attenuation
Does not cause additional environmental impact from response activities
  • Only suitable for relatively light products when there is no threat to human life or sensitive environment
  • Public perception that nothing is being done
  • Requires dedicated monitoring efforts
  • If conditions change, calling for other response options, the slick could be weathered and inhibit their effective application
Slick could be transported to uncontaminated or sensitive areas
Mechanical Recovery
  • Removes oil from the water surface
  • Widely accepted first response option
  • Works on most fresh and weathered oil types (large window of opportunity)
  • Good availability of equipment and expertise
  • Recovered product may be reprocessed
  • Requires collection of oil by booms, which is not effective in high seas, for spread-out thin slicks, or large-volume spills
  • Recovery of oil in ice is challenging
  • Challenges with resource mobilization to remote offshore location before oil spreads too thin
  • Only limited oil volume can be concentrated by booms and made available for recovery
  • Slow collection and recovery process
  • Very labor and equipment intensive
  • Large volumes of free water are often recovered together with oil
  • Requires storage for the recovered product
  • Challenges with transport and disposal of recovered product in remote regions
  • Operations are often limited to daylight
  • Additional environmental impacts (e.g., air quality, noise) due to the need for large number of vessels for extended periods of time
  • Oil that was not collected and recovered will continue to drift into clean areas and can potentially reach shorelines or sensitive environments
  • Impacts associated with transport, storage, and disposal of recovered oil and water, especially in remote and limited infrastructure regions
  • Exposes responders to hydrocarbons and risks involving personnel safety
  • Impacts to seagrass, corals, and sensitive benthic environments during nearshore or shallow water response
In Situ Burning
  • Can quickly remove up to 98% of oil that was collected within booms or by herders
  • Reduction of hazardous/flammable vapors
  • Lower logistics and equipment requirements than mechanical recovery
  • Storage and waste disposal are typically minimal or not required
  • Minimal additional environmental impact in most cases
  • Effective at low temperatures and for oil in ice
  • Ignition of the well could eliminate large volumes of oil and gas directly at the source
  • Requires specialized equipment and expertise for application and monitoring
  • Requires regulatory approvals and may generate public concerns
  • Typically conducted offshore away from populated areas
  • Requires collection of oil by booms or herders, which is not effective in high seas or on spread-out thin slicks
  • Only limited oil volume can be concentrated by booms. Slow collection process
  • Works better on fresh oil. Not effective on emulsified oil, resulting in limited window of opportunity
  • Daylight operations only
  • Localized and temporary decrease in air quality
  • High temperature impacts in the water column are minimal and only in already affected area/volume
  • Residue may adversely affect sensitive benthic environments and thus have to be recovered in some cases
  • Oil that was not collected and burned will continue to drift into clean areas and may reach sensitive habitats
  • Safety protocols and proper PPE should be used to reduce exposure of responders to fire and emmissions
Dispersants: Surface Application
  • Dispersant planes can get to a spill site and begin response quicker than other response techniques
  • Can remove large volumes of oil from the surface quickly, preventing it from coming to the shore and affecting sensitive environments
  • Enhances natural dilution and biodegradation
  • No storage or disposal issues
  • Minimal equipment and manpower requirements
  • Aerial use eliminates exposure of personnel to hydrocarbons or the need for labor- and equipment-intensive on-water recovery operations
  • Effective in turbulent sea conditions that would hinder effectiveness of mechanical recovery and in situ burning (e.g., wave height greater than 4–6 ft)
  • Icebreakers can create mixing energy to disperse oil in ice
  • Requires specialized equipment and expertise for application and monitoring
  • Daylight operations for aerial spraying; vessels could potentially spray at night
  • Requires regulatory approvals and may generate public concerns
  • Requires wave action to create oil droplets and mix them into a water column.
  • Cannot be used in very high winds which prevent safe aerial operations and accurate targeting of the slick with dispersants (e.g., wind speed over 35 knots)
  • Limited window of opportunity (most effective on fresh light or medium products at temperatures above pour point)
  • Requires sufficient volume of water for dilution; use in shallow waters requires NEBA/SIMA analysis
  • Public perception issues
  • Localized and temporary decrease in water quality
  • Exposes organisms in the top portion of water column to higher concentrations of hydrocarbons
  • In waters with high sediment and organics content, high concentrations of hydrocarbons could potentially result in marine oil snow formation and transport of degraded oil components to benthic environment
  • Application from the vessel may result in exposure of responders to dispersants; appropriate PPE should be used
  • May result in formation of aerosols, creation of which should be weighed against impacts of natural evaporation of undispersed slick
  • Undispersed oil will continue to drift into clean areas and may reach sensitive habitats
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Benefits Challenges Potential Impacts
Dispersants: Subsea Application
  • Large oil volumes can be treated immediately at the source with high effectiveness
  • Prevents oil from reaching the surface, forming slicks and clouds of VOCs; enables source control operations
  • If efficient, in some scenarios can eliminate/reduce the need for surface recovery, in situ burning, and surface dispersant operations, thereby reducing the potential for exposure and accidents during these operations
  • Reduces/eliminates challenges with handling, storage, and disposal of large volumes of waste that could otherwise be generated by on-water mechanical recovery or shoreline cleanup
  • Keeps hydrocarbons away from sensitive habitats and areas with high densities of organisms at sensitive life stages (exception is coral reefs if present)
  • Keeps hydrocarbons away from sunlight that may increase their overall toxicity and impacts
  • The only response option suitable for any weather and 24/7 operations
  • Requires reduced dispersant-to-oil ratio compared to surface spraying operations
  • High degree of control over dispersant application process
  • Sufficient water volume available for dilution
  • Reallocates oil to areas with smaller biological density than at the water surface or at nearshore/shoreline areas
  • Requires regulatory approvals and may generate public concerns
  • Requires specialized equipment and expertise for application and monitoring
  • Public perception issues
  • Relies on a blowout turbulence for generation and mixing/dilution of droplets
  • Significantly increases volume of dispersed oil in the water column, including in the trap layer; increases exposure of some aquatic organisms to hydrocarbons and potentially reduced oxygen levels
  • Can expose benthic organisms to dispersed oil
  • In waters with high sediment and organics, high concentrations of hydrocarbons could potentially result in marine oil snow formation and transport of degraded oil components to benthic environment
  • Undispersed oil will continue to drift into clean areas and may reach sensitive habitats.

interests. Spill responders and oil spill scientists recognize that there is no single cleanup method that is effective in every situation and that all cleanup activities are a tradeoff, in response to an already existing detrimental pollution event.

Oil spill history has shown that the greatest impact to people and to the environment happens when oil reaches sensitive nearshore and shoreline areas (refer to Chapters 5 and 6 for more details). This is because these areas have higher densities of organisms than offshore or deepwater areas, and those organisms are often at sensitive life stages. Oil arriving to shallow waters can be present in relatively high concentrations, can accumulate on shorelines over time, and can be quite persistent. This overlap of high biological density and high concentrations of persistent oil should be avoided to the extent possible. Cleanup activities, however effective, can create additional impacts, as they often involve large numbers of people and equipment for long periods of time and generate large volumes of waste. Exclusion, deflection, diversion, and collection shoreline booming strategies are deployed to reduce the consequences of an oil spill reaching the shore and provide protection to critical habitats.

Unfortunately, due to the nature of booming operations, booms can only protect relatively small sections of the shoreline. Important tradeoffs must be evaluated when deciding where and when to place booms. Booms take time to deploy; once deployed, they take additional time to tend and relocate. Booms have to be managed from vessels and placed at an angle, rather than perpendicular to the oil slick trajectory; booming will not be effective if not placed at an angle as oil will be pushed over or under the boom. If left unattended, booms can be affected by tides and currents, lose function, and be dislocated and pushed into sensitive shorelines resulting in an additional environmental impact. This was illustrated during the DWH response when long stretches of boom deployed parallel to the shore were not able to stop oil from coming to shore and created additional environmental impacts when they were pushed into marshes requiring complicated retrieval operations. Exclusion and deflection booming strategies are not designed to remove oil from the environment, only to divert the slick to another location. Hence, they are used to protect relatively short stretches of the most sensitive locations such as inlets into back water or small estuaries (API, 2014, 2016b). Attention should be focused on the location to which the oil is diverted to prevent additional harm to the environment. Diversion booming aims to direct oil to a dedicated collection location, but it is often more suitable for responses in rivers, when oil moves parallel to the shore, rather than the offshore environment when an

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

TABLE 4.3 Applicability and Likely Effectiveness of Sunken Oil Recovery Techniques

Red = not likely effective; yellow = may be effective; green = most likely effective
Suction Dredge Diver Vacuum Diver Pump Excavator Grab Dredge Environmental Clamshell Sorbents/V-SORS Trawls and Nets Manual Removal Shallow Water Manual Removal by Divers Agitation/Refloat
Water Depth (ft)
— <5ft
— 5 to 40 ft
— 40 to 80 ft
— >80 ft
Water Visibility
— >5 ft
— <5 ft
Water Current
— <1 kt
— 1 to 2 kt
— >2 kt
Water Height (ft)
— <2 ft
— >2 ft
Availability
Oil Pumpability
— Fluid
— Not Fluid
Oil Distribution
— <10 %
— 10 to 50 %
— >50 %
Oil Patch Size
— <0.1 ft2
— 0.1 to 1 ft2
— >1 to 10 ft2
— >10 ft2
Substrate Type
— Sandy
— Muddy
Bottom Obstructions
Buried Oil
Sensitive Habitat
Removal Rate*
Waste Generation**
Environmental Impact**
Cost **
*Classified as rapid, medium, or slow.
**Classified as low, medium, or high.

SOURCE: API Technical Report 1154-2, First Edition, February 2016. Reproduced with permission from the American Petroleum Institute.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

oil slick approaches the shoreline as a large front. Shoreline Protection Guide for Sand Beaches (API, 2013) describes additional tactics such as dams, dikes, and barriers that could be implemented to protect and reduce the spread of oil on sandy beaches as well as response and environmental considerations that should be considered in selection of these strategies.

When an oil slick arrives to shore, it may affect environmentally sensitive areas as well as areas sociologically, economically and culturally important to humans, such as areas of recreation, fishing, industry, and tourism. Depending on the characteristics, type, and sensitivity of the shoreline and the physical and chemical properties of the oil itself (amount, type, and degree of weathering), various methodologies may be employed to mitigate an oiling event (NOAA, 2010). Cleanup activities can range from the allowance of natural attenuation of the oil, to intrusive manual and mechanical removal of the oil. Careful consideration should be given to any additional environmental and socioeconomic impacts that could result from the implementation of these techniques (Hoff, 1996; Martínez et al., 2012; Michel and Ruherford, 2014; Michel et al., 2017). Numerous cleanup methodologies have been developed, all of which are part of the available response toolkit. The predominant cleanup methods and responses, and their efficacy, their advantages and disadvantages are discussed in Appendix E, Shoreline Cleanup Methodologies. Oil deposited on a surface may be removed by manual methods such as a hand rake and shovel, sorbents, or by mechanical methods such as maintainers/road graders and small front-end loaders, skimmers, and vacuum systems. Purpose-built mechanical beach cleaners and sand sifters can sometimes be utilized; some of those are designed to minimize the removal of valuable sediment material along with the oil (API, 2013; Michel et al., 2017). Oil that has adhered to a substrate may necessitate the use of chemicals for removal or may be removed by the use of water washing utilizing varying degrees of pressure and temperatures. Other response strategies also exist, including bioremediation, debris removal, and tilling.

The choice of oil removal response technique(s) is always a tradeoff among efficacy, expedience, safety, and environmental impact of the cleanup, which must be considered in each event. For example, complete removal of the oil contamination is often not a desirable endpoint, as such a degree of removal may often cause more damage to flora and fauna through direct secondary impacts or through stress to vulnerable species. Also, even minimal human cleanup activities may affect feeding behavior of certain species, such as threatened or endangered foraging birds, and thus are subject to provisions under the Endangered Species Act. These provisions require the overseeing federal entities to engage with the U.S. Fish and Wildlife and National Marine Fisheries Services, dependent on the identified species that may be affected, in a consultation process (U.S. Congress, Senate Committee on Environment, 1983).

The physical intrusion into an area, for the purposes of an oil spill assessment or cleanup, can have unintentional and potentially detrimental consequences that can worsen an already bad situation. Spill response equipment and even response personnel can create secondary—sometimes greater—impacts than would have been seen had the intrusion not occurred. Heavy equipment, response measures, and even foot traffic can damage the established biota of a locale through trampling or flattening, particularly by heavy tracked equipment or in areas of soft substrate. Equipment movement and response strategies, such as berms and barriers, can change the topology of an area, causing impediments to organisms that depend on the area, such as nesting sea turtles, or alter the area’s natural hydrology, potentially causing long-term changes to an entire area. Intrusive response strategies such as building sand berms, inlets restrictions, and freshwater diversion into coastal marshes should be carefully evaluated, as they can result in greater environmental impacts than the oiling itself (Martínez et al., 2012). Refer to Section 4.2.5 for the best practices in comparing response options and their potential consequences. Oil that was once on the surface, subject to natural degradation processes, can be driven into the substrate where the lack of oxygen can cause the material to remain for many years (Beland et al., 2017). Additionally, shoreline response typically generates a large volume of waste that has to be collected, stored, transported, and disposed of. This can create additional environmental impacts and logistical challenges. These and many other considerations must be thoughtfully analyzed by knowledgeable and experienced response personnel to ensure that the most appropriate treatment strategy is selected.

Marine shoreline ecosystems that may be affected by spilled oil are highly variable in geophysical structure as well as resident and transient morphological composition (refer to Chapter 5 and Appendix G for more details on oil fate and behavior on shorelines). Oil stranding on a fine-grained sand beach will require different protection and cleanup methodologies than oil affecting a rocky shoreline or marsh environment. The fate and behavior of oil, once it comes ashore, must also be considered in response and protection strategies. The oil spilled and affecting a shoreline in tropical or temperate climates may require a different cleanup strategy than the same oil in an Arctic environment. As in the open ocean marine environment, natural biodegradation and chemical composition continually alter an oil’s makeup, which may in turn necessitate changes in the response strategies chosen. Oil that was once amenable to one strategy can change, sometimes rather quickly, to a point that the initial strategy no longer works. Most common cleanup methods and response techniques are illustrated in Figure 4.16 and described in Appendix E. Table 4.4 summarizes benefits, challenges, and potential impacts of various methods.

4.2.4.1 Advanced Shoreline Cleanup Techniques

Although every shoreline cleanup technique presents certain challenges and tradeoffs, several of them require special

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Image
FIGURE 4.16 Examples of shoreline oil spill response operations.
SOURCE: Image provided courtesy of the American Petroleum Institute, produced by Iron Octopus Productions, Inc.

regulatory approvals, scientific information, and additional considerations (see Section 4.2.5).

Surface Washing Agents

Surface washing agents (SWAs) are specially designed chemicals, composed of a surfactant and sometimes solvent, that are used to loosen heavily coated or stubborn oils on surfaces; the oils can then be more easily removed by wiping with sorbents or water washing techniques that move the oil into another location for removal by other methods. SWAs used in marine oil spill response fall into two categories: “lift and float” and “lift and disperse.” As with all chemical countermeasures, use of SWAs must be approved by the designated agencies. In the United States, Subpart J of the National Oil and Hazardous Substances Pollution Contingency Plan (National Contingency Plan), which lists approved surface washing agents does not distinguish between the categories of “lift and float” or “lift and disperse,” but only surface washing agents shown to float the oil after application are typically allowed for use in the marine environment. The method allows the floating oil to be corralled and collected for removal and disposal. Subpart J also requires that the overseeing federal jurisdictional entity, usually the U.S. EPA or USCG, request permission from their local Regional Response Team prior to use. Some industrial locations have gone through the preauthorization process for use of SWAs, expediting cleanup operations in locations where environmental impacts have been considered and deemed an acceptable risk.

Burning of Oil in Marshes

In situ burning of oil in marshes involves the controlled incineration of an oil product that has affected a salt or brackish marsh (Fingas, 2018). Often oil that has affected marsh vegetation becomes trapped within it and becomes inaccessible for mitigation by other cleanup measures. The dense cover of some marsh inhibits evaporative processes on the oil, which may have a long retention time especially if it penetrates into the marsh sediments. Many species utilize marsh habitat for forage and refuge, thus creating the possibility of secondary oiling from this remaining oil. Though burning of oil in marshes can have very high efficacy rates (up to 70% reported by NOAA in some cases), there are numerous tradeoffs and precautions that must be taken when

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

TABLE 4.4 Benefits, Challenges, and Potential Impacts of Shoreline Cleanup Methods

Benefits Challenges Potential Impacts
Debris Removal
  • Removal of debris before impact lessens the amount of hazmat material that potentially may have to be disposed
  • Allows for an unobstructed work zone for cleanup and response activates to occur
  • Very labor-intensive and time-consuming
  • May place responders in situations of potentially hazardous conditions causing concerns about human health and safety
  • Removes material that may be used as forage or shelter for local biota
  • Removes material that may stabilize an area from erosion
  • Equipment and personnel can inflict secondary impacts on flora and fauna
Monitored Natural Attenuation
  • Does not cause additional environmental impacts from response activities or generate a waste stream
  • Time-consuming and not suitable for all oil products
  • Requires emendable environmental conditions to be an effective response option
  • Potential environmental impacts from persistent oils
  • Possible remobilization to uncontaminated or sensitive areas
Tilling/Aeration
  • Often used to augment natural attenuation
  • Allows oil to be more rapidly and naturally broken down by natural processes by increasing accessibility to nutrients and oxygen and by increasing the surface area of the oil for colonization of microbes
  • Requires mobilization of light, medium, or heavy equipment to remote locations
  • Time-consuming strategy, that relies on natural processes to remove the oil
  • Equipment and personnel can inflict secondary impacts on flora and fauna
  • Potential of disturbance of local fauna from noise and activity
  • Process moves oil to new locations and can potentially bring previously non-exposed organisms into contact with the oil
  • Potential disruption of subterranean fauna
Bioremediation (Microbial, Nutrient Enrichment, Enzymatic)
  • Enhances natural biodegradation and lets microbes convert the oil into inert byproducts
  • Low physical disturbance of affected area
  • Ease of use
  • Slow process of removal and not suitable for all oil products
  • Requires emendable environmental conditions to be an effective response option
  • May require addition of nutrient enrichment, which may have secondary effects
  • May be used in conjunction with tilling (aeration)
  • Oxygen and nutrient addition are typically more effective and accepted than bacterial seeding
  • Slow process that may allow for secondary impacts to organisms by contact or ingestion
  • Possible remobilization to more sensitive locales by being transported to uncontaminated or sensitive areas
Surfwashing
  • Removes oil from contaminated sand and gravel by relocating the material into nearby waters, utilizing the natural wave and water flow to help dislodge and naturally remove the contamination
  • Allows for large area of contaminated shoreline to be remediated
  • No additional waste is generated
  • Requires mobilization of light, medium, or heavy equipment to remote locations
  • Additional environmental impacts to substrate and flora should be expected due to damage from equipment mobilization and use
  • Potential of disturbance of local fauna from noise and activity
  • Process moves oil to new locations and can potentially bring previously non-exposed organisms into contact with the oil
  • Potential disruption of subterranean fauna
  • Potential for removal of valuable non-contaminated substrate and material by inexperienced responders
Manual Removal
  • Can be an effective, surgical removal option with minimal secondary impacts when only the contamination is removed
  • Generates a low volume of waste material
  • Very labor-intensive and time-consuming
  • May require responders to be in remote areas, in close contact with potentially hazardous materials, causing concerns about human health and safety
  • Can inflict secondary impacts to flora and fauna
  • Risks removal of valuable non-contaminated substrate and material by inexperienced responders
  • Can generate additional waste requiring storage, transportation, and disposal
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×
Benefits Challenges Potential Impacts
Vegetation Cutting
  • Removes oiled vegetation and allows access to areas of oil accumulation beneath the canopy for removal
  • Eliminates secondary oiling of biota that may utilize the area for forage or shelter
  • Very labor-intensive and time-consuming
  • May require responders to be in remote areas, in close contact with potentially hazardous materials, causing concerns about human health and safety
  • Consultation with professionals should dictate use of this method as many tradeoffs must be considered
  • Generates a high volume of waste material that must be properly disposed
  • May cause long-term habitat loss due to the area of plant removal
  • Equipment and personnel can inflict secondary impacts on flora and fauna

this type of response is considered.5 The NOAA/API Guide on Oil Spills in Marshes (2013) identified and described 30 oil spills, three field experiments, and three laboratory studies concerning in situ burning conducted in marshes. Of the 27 oil spills reviewed, 23 were light to medium crude oils and 4 were light refined products. The NOAA guide also discussed various parameters that will affect feasibility and effectiveness of burning and concluded that if burning is conducted following appropriate guidelines, the wetland vegetation is expected to recover within 5 years, but for many spills within one to two growing seasons.

Federal, local, and state agencies involved in emergency response and protection of the air quality must be consulted and authorize the burning technique. These entities will consider the amount of air pollution impacts including particulate matter that will be emitted and potentially affected areas of populations downwind (see Section 4.2.3.3). Other entities such as federal, state, and tribal authorities, along with historical and cultural authorities, should be consulted. Threatened and endangered species as well as other local flora and fauna must be identified and protected using numerous methodologies. If the ignition of the oil in the marsh requires the use of a chemical accelerant or ignition agent, this may require additional approval.

Numerous considerations must be addressed when evaluating oil burning in marshes (NOAA and API, 2013). This may include time of the year, the type and weathering condition of oil, soil type and degree of oil penetration, wind speed, water depth (if applicable to protect vulnerable vegetative root systems), containment of the burn, etc. Containment of a burn in a marsh is difficult, as the installation of protective fire boom is typically not possible due to the vegetation coverage. Fire spreading is typically prevented by creating corridors of open water separating out the burn area. Numerous response organizations have developed checklists and guidance documents for undertaking safe burning operations (API, 2015b).

Bioremediation

Bioremediation, biostimulation, and bioaugmentation are response strategies that utilize naturally occurring or introduced microbial biodegraders to consume the oil, resulting in breakdown of some of its components, predominantly into carbon dioxide and water (API, 2014). Bioremediation has been and still is a tested form for spill response on land spills where there may be a limitation of microbes or nutrients and there is sufficient time and proper conditions for the processes to work. On marine shorelines bioremediation is most often incorporated as a “polishing” step or response to augment the natural degradation processes after gross oil contamination has been removed and continued cleanup would cause more harm than benefit.

Three types of bioremediation methodologies are discussed here; each aligns within one or both categories of biostimulation or bioaugmentation:

  1. Nutrient enrichment/addition—stimulates naturally occurring bacterial communities by the addition of limited essential nutrients to accelerate the degradation process.
  2. Microbial addition—involves the addition of petroleum hydrocarbon-degrading bacteria/biodegraders directly to an oil that has been released into the environment for the purpose of exponentially increasing their numbers to expedite the degradation process.
  3. Enzyme addition—this process is meant to accelerate the natural degradation processes by the addition of a catalyst that speeds the chemical reaction rate of a particular reaction, thereby expediting the natural breakdown processes.

Biostimulation involves the judicious addition of chemical supplements (typically sources of nitrogen and/or phosphorus, often in commercial formulations) that assist indigenous

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5 See https://www7.nau.edu/itep/main/HazSubMap/docs/OilSpill/USGSOSRinFastCurrents.pdf; https://oilspillprevention.org/-/media/Oil-Spill-Prevention/spillprevention/r-and-d/inland/swift-water-spill-response-guide-april-2.pdf; https://www.itopf.org/fileadmin/uploads/itopf/data/Documents/TIPS_TAPS_new/TIP_3_Use_of_Booms_in_Oil_Pollution_Response.pdf; and https://www.osti.gov/etdeweb/biblio/20103189.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

hydrocarbon-degrading microbes to metabolize oil components by balancing the in situ carbon:nitrogen:phosphorus ratio. Addition of nutrients does not usually increase the mass or range of hydrocarbons eventually degraded, but rather accelerates the rate of biodegradation (reviewed by Prince, 1993). Biostimulation, where permitted, may be most useful on nutrient-poor beaches where the applications can be controlled and not immediately be diluted by wave and tidal action. Several types of nutrient application, including solid and slow-release oleophilic fertilizers, were used successfully on shorelines after the Exxon Valdez spill in Alaska; some were found to increase biodegradation rates three- to five-fold (Atlas, 1995). However, in field trials of other near-shore environments (e.g., Delaware shoreline and salt marshes; Mearns et al., 1997; Zhu et al., 2001), the application of nutrients was found to be unnecessary because terrestrial runoff supplied sufficient nitrogen and phosphorus. Biostimulation using oleophilic fertilizers may be particularly useful on beaches for accelerated degradation of buried oil in sandy intertidal (aerated) beach sediments (Pontes et al., 2013), but whether biostimulation of fine-grained marine sediments would enhance anaerobic biodegradation is untested in the field. More recently, in vitro trials with seawater microcosms combined nutrient supplementation with application of biosurfactants, resulting in enrichment of native hydrocarbon-degrading species and greater biodegradation than that achieved using either nutrients or biosurfactant alone (McKew et al., 2007). However, biostimulation for remediation of oil spills in the open ocean is unlikely to be successful because of dilution factors and therefore has not been rigorously field tested.

Bioaugmentation (“seeding”) is the addition of exogenous microbes to an environment. In the case of oil spills, bioaugementation involves introducing a known hydrocarbon-degrading species or cocktail of species previously enriched during growth on oil in a laboratory or commercial facility. Although bioaugmentation can be successful at small scale in vitro (e.g., McKew et al., 2007) and large scale ex situ (Hassanshahian et al., 2014), bioaugmentation remains controversial and currently is not implemented in situ for marine oil spills, for several reasons. First, introducing exogenous microbial cultures into a natural environment is not permitted in some jurisdictions. Second, the survival and transport of introduced microbes cannot be controlled once they are released into an open environment. Third, it is well established that the indigenous oil degraders that exist in every marine ecosystem examined to date are adapted to the local conditions and predators at any given spill site, whereas introduced microbes are at a disadvantage and may not compete with indigenous microbes. Finally, introduced organisms would be subject to the same environmental limitations as the native organisms and may still require biostimulation. New approaches—for example, immobilization of bacteria in pellets of biodegradable floating support material (Luo et al., 2021)—may revive interest in testing this strategy for confined oil slicks.

Enzyme addition involves distributing a formulation of one or more cell-free enzymes to the environment. However, several inherent limitations make this option unlikely to be effective in situ. Among these are the facts that (1) hydrocarbon oxidation requires multiple enzymatic steps that cannot be achieved by a single enzyme, and suspensions of enzyme mixtures cannot be coordinated into an efficient pathway in a dilute environment; (2) many enzymes require sensitive co-factors that would have to be supplied in a protected matrix; and (3) enzymes are proteins and therefore likely to be consumed as nutrients by native microbiota before they are able to effect a change in the oil.

Arctic Shoreline Response

The Arctic environment presents some unique challenges, especially for the shoreline cleanup. Limited daylight hours during winter, frequent days with fog, strong wind gusts, and low temperatures can make any outdoor activities very difficult. Limited infrastructure presents another obstacle to field operations. Above the Arctic circle in North America, there are no rail connections, two deep-water ports, only one of which (Tuktoyaktuk, in the western Northwest Territories of Canada) is connected to the road system, and four airports open to regularly scheduled jet aircraft service, three of which are in Alaska. Travel from these airports to more remote field sites usually requires small chartered aircraft. There are very few settlements in the Arctic and they are not likely to accommodate large number of workers that may be required for the shoreline cleanup. Challenging environmental conditions, limited transportation options, difficulties with accommodating large number of personnel and equipment in the remote and often sensitive areas makes planning and implementing Arctic shoreline response very difficult. Arctic shoreline types vary from rocky shores and gravel and sandy beaches that are similar to more temperate regions to some unique shoreline types such as tundra cliffs and peat shorelines. The sensitive nature of Arctic shorelines require special considerations for oil spill assessment and cleanup. Under some circumstances, monitored natural attenuation may be the most appropriate response method, especially considering logistics challenges in remote regions. In addition to the challenges of bringing equipment and personnel to the remote beaches and accommodating them for long periods of time without existing infrastructure, the negative impacts of large volumes of waste that would get generated and additional disturbance from human presence has to be carefully considered as they may outweigh benefits of cleanup. One positive aspect of the Arctic environment is that landfast ice (ice cover growing from the shore toward the sea) forms first and melts last, providing shorelines with natural barriers from offshore oil spills for a significant portion of the year. An oil spill heading toward the shore will accumulate against the ice edge where it can be effectively recovered or burned using the techniques described in earlier sections. The frozen nature

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

of the ground during significant portions of the year also prevents penetration of pollution deep into the soil and may allow for a successful recovery from the surface. Emergency Prevention, Preparedness and Response (EPPR) Guide to Oil Spill Response in Snow and Ice Conditions (2015) provides a comprehensive overview of Arctic shoreline types, expected oil behavior, and recommended response strategies.

4.2.5 Comparison of Response Options for Decision-Making

As discussed in earlier sections, no response option is completely effective under every condition or completely risk free. Every response action, as well as inaction, can result in additional impacts, which must be carefully considered before the decision to proceed is made. In the preparedness phase or at the time of an oil spill, decision-makers need to evaluate possible response strategies—their advantages, challenges, and additional impacts they my cause—and ultimately select those that would be optimal for a specific spill scenario. Without this consideration, the response actions could result in greater impacts than the oiling itself and delay the environmental and socioeconomic recovery of the affected areas (Hoff, 1996; Martínez et al., 2012; Michel and Ruherford, 2014; Michel et al., 2017).

Depending on the scale and complexity of the spill scenario and the phase of planning or response, this analysis may range from a mental health assessment and a brief discussion to a comprehensive analysis including formal ecological and socioeconomic assessment and involving a variety of stakeholders. The essence of the principle “minimize the harm” is integrated into all steps of contingency planning and response even if a formal analysis is not conducted. Some of the examples include:

  • Contingency planning, incorporating the entire toolbox of response options and allowing flexibility of utilization of individual tactics at the time of response;
  • Focus of the initial response on stopping the spill source and minimize oil spreading;
  • Setting response objectives aiming “to minimize harm to the environment” and “protect resources at risk”;
  • Development of response technique checklists and decision trees by regulatory bodies to expedite decision-making process at the time of the response; and
  • Pre-authorized and designated “no use” dispersant zones in offshore United States areas that have been established, based on consensus, from previously conducted analysis.

In fact, many small spills or responses, where only one response method can be used (e.g., mechanical recovery) do not require comparative analysis; responders can use best operational practices and existing contingency plans to respond to a spill of this nature. In the case of a larger spill, when several response options are viable, a comparison between response options can be conducted in several ways, all comparative analyses are built on the same principles and aim to engage with key stakeholders, minimize impacts on people and the environment, and assist with the most efficient and effective recovery of the ecosystem (including the local community). The primary concern of any response is the safety of the public and responders. Once action is taken to protect human health and safety, comparison of response options can be analyzed. This process can be applied with different degrees of involvedness while maintaining the same “minimize the harm” principle based on the nature of the event and the timing of the decision (during contingency planning or the response phase). NEBA is a comparison tool historically used by stakeholders and the response community to analyze response options and create a response strategy that minimizes the effect of an oil spill on both the environment and local community.

It is important to note that a formal NEBA process may be time- and resource-consuming and when possible, should be conducted as a part of the contingency planning process guiding the response strategies used for planning scenarios. It may be difficult to conduct a comprehensive formal NEBA analysis from scratch at the time of a spill without causing unnecessary delays in spill response. During a response, the NEBA process (formal or informal) is generally performed by the environmental unit and used to ensure that response strategies and tactics are tailored to the evolving spill-specific conditions and offer maximum protection to the resources at risk. The environmental unit specialists can use NEBA scenarios generated during planning phase and adjust them for the specifics of a spill.

Whether conducted formally or informally, the NEBA process typically consists of the following steps (IPIECA, 2015):

  1. Compile and evaluate available information.
  2. Develop response scenarios, including a “no response” scenario as a base case. Evaluate their effectiveness and resulting changes in the oil fate and behavior.
  3. Identify environmental and socioeconomic resources that may be affected under different response scenarios.
  4. Evaluate potential impacts to the resources and their recovery potential under different response scenarios, including potential additional impacts of response activities.
  5. Compare potential outcomes and select response option(s) resulting in a higher degree of environmental and socioeconomic protection and fastest ecosystem and economic recovery.

There are several methods for implementing NEBA principles in a formal assessment of response options (NASEM, 2020). These are:

  • Consensus Ecological Risk Assessment (CERA)
  • Spill Impact Mitigation Assessment (SIMA)
  • Comparative Risk Assessment (CRA)
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
×

All these methods are based on similar considerations:

  • Safety of public and responders is addressed first.
  • A critical assumption is made that oil is already in the environment and response options will change the oil’s presence in varying environmental conditions. Impacts of both untreated slicks and slicks treated through various response tools need to be weighed.
  • All feasible response options are considered (Response Toolbox approach).
  • No response methods will be completely effective and all response efforts pose some level of risk.
  • Realistic effectiveness of response techniques are considered under conditions unique to each spill.
  • Consider all affected resources and use an ecosystem-based approach to assess impacts to populations and habitats together, rather than assessing impacts to individual organisms.
  • Incorporate evaluation of socioeconomic and cultural resources, if needed.
  • Take a holistic view to appraise long-term impacts on the public and the affected ecosystem and consider recovery rates of affected resources to their pre-spill condition.
  • Rely on best available science and location-specific information when available.
  • Encourage stakeholder engagement and transparency of decision-making. Local and Indigenous knowledge on topics such as baseline conditions, environmental patterns, resources at risk and protection priorities, temporal and spatial population variability, recovery rates, etc., should be sought and incorporated into the analysis to ensure appropriateness and transparency of response decision-making.

4.2.5.1 Consensus Ecological Risk Assessment

The USCG sponsored 17 CERA workshops from 1998 to 2012 (Aurand et al., 2000). These workshops brought together a variety of stakeholders who conducted a formal NEBA using comparative risk methodology to evaluate regional oil spill response options in a planning environment. More recently, two additional CERA workshops were held: one focused on potential transportation-related Bakken and dilbit crude oil spills in Delaware Bay (sponsored by USCG; published in 2016) and one in Hawaii (sponsored by Oceania RRT; published in 2018). The CERA workshops present a valuable mechanism to bring together and build working relationships among key stakeholders, educate them on and involve them into the decision-making process, compile available regional information and best practices, and facilitate timely selection of response options at the time of response. The outcomes of these workshops may need to be periodically reviewed to ensure that they are still relevant for the ever-changing spill scenarios, environmental conditions, best available science, and resources protection priorities.

In the CERA framework, a response scenario is developed with specific detailed information on oil composition, toxicity, weathering, and trajectory. The scenario, response options and evaluation of the impact of the response options are developed by a group of diverse stakeholders to evaluate the impacts of different response options, including no response. The affected environment is divided up into a number of compartments (e.g., water, shoreline, socioeconomic resources, etc.). Each compartment is defined by its representative population or resources and its relationship to the other defined compartments. This results in a risk-ranking matrix in which the affected resources are ranked by the percent of a population/habitat affected and the rate of its recovery. The most affected and slower-to-recover populations and habitats receive higher risk scores; the populations and habitats affected to a lesser degree and capable of rapid recovery receive lower risk scores. This comprehensive analysis, conducted in coastal regions in the United States led to the designation of the pre-authorized offshore zones for dispersants and in situ burning as well as the development of checklists and decision trees that could be used in an emergency. The CERA method proves challenging because of the necessary amount of scientific information and time required for analysis. It may not be appropriate for short response efforts or when detailed information is not available. The SIMA method was recently developed to address this need.

4.2.5.2 Spill Impact Mitigation Assessment

SIMA underscores the importance of stakeholder engagement and depends on practical experience, best available data, and local knowledge to expeditiously evaluate response options, even with limited information. It also specifically addresses the socioeconomic, cultural, and special value resources of local stakeholders (IPIECA and IOGP, 2018). In the contingency planning phase, this approach could be used with the same intricacy and thoroughness as the CERA methodology, but during a time-critical response phase, it could be done much faster. Similar to CERA, SIMA identifies compartments within the potentially affected environment and assesses the impacts with and without response measures. When the impacts are assessed, the process uses consensus opinion of experts and stakeholders to assign relative impact ranking for different compartments. Then the group evaluates the response options and for each compartment determines whether a response option improves the situation or creates additional impacts, as well as the degree of improvement or additional negative effects. These assessments are based on expert knowledge and best available information and are translated into a numerical matrix by first assigning an initial impact coefficient and then multiplying it by a mitigation factor. Scores for each response technique are then summed up across all compartments. A higher positive SIMA score indicates the likely ability of a response technique to mitigate impact from the spill. Negative SIMA scores indicate

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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that a response technique may result in greater damage than an unmitigated slick. This analysis helps responders and decision-makers to select response techniques that would be most suitable under a specific spill scenario.

It is important to note that, under different response options, the numerical value of SIMA scores may be misunderstood as having greater precision than was intended by this methodology. In a simplified form, the SIMA converts professional opinions into numeric scores; these numbers should not be taken as absolute values, but rather used as a relative comparison metric. Small single digit differences between impact mitigation scores do not indicate that one technique is better than the other. Generally speaking, positive values indicate response techniques that have a potential to result in a reduction of spill impacts and negative scores highlight the techniques that may result in additional environmental impacts.

4.2.5.3 Comparative Risk Assessment

The CRA is a new, computationally advanced approach to the comparison of response techniques and their potential effects (Bock et al., 2018; French-McCay et al., 2018; Walker et al., 2018). This assessment is similar in process to CERA in terms of identifying compartments and representative populations within each compartment. However, a CRA takes a more quantitative approach that involves complex three-dimensional numerical modeling to calculate the volume of water and the area of the water’s surface that is affected by the oil concentrations above the impact threshold. The results are then overlapped with the relative density distributions of valuable ecosystem components (VECs) across environmental compartments. A risk coefficient is then assigned based on the population’s sensitivity, vulnerability, and recovery rates. As in most risk assessments, the organisms that are slowest to reproduce and those that are long-lived appear to be at greatest risk and come up at the top of protection priority (Bock et al., 2018; French-McCay et al., 2018).

The international community may use other numerical modeling methods, which are not typically used in North America.

Summary

During oil spill preparedness, planning, and response, the response community and stakeholders use NEBA, CERA, SIMA, CRA, and other techniques to develop a response strategy. Using these approaches, either formally or informally, ensures the response strategy compares the impact mitigation potential of each response option while minimizing the net impact of an oil spill on the environmental, socioeconomic, and cultural resources at risk. Conducting a formal NEBA, CERA, SIMA, CRA process is not always feasible or practical, yet there is always a need to base response decisions on the best available information in a timely way. Lessons learned from the earlier assessments in a particular region, assessments administered for similar scenarios in other areas, and experiences from oil spill responses and restoration projects, globally, could be used to facilitate timely, informed, and transparent decision-making. Responders can use an earlier formal analysis when a spill takes place in an area that is already covered by a NEBA-type of analysis. If the actual spill scenario and NEBA-type analysis are reasonably similar, a significant portion of the earlier analysis and conclusions can be used to expedite the decision-making process (with some quick adjustments to reflect specifics of the new scenario).

It should be noted that the NEBA-type processes are quite distinct from the NRDA process. The NEBA framework attempts to integrate all available knowledge about the impacts of oil in different compartments and evaluates the ability of response techniques to mitigate them. It starts with an assumption that oil is already in the environment and seeks to find an optimal response solution, recognizing that none of the response techniques are 100% effective and that all of them come with their own risks. This analysis can be performed reasonably quickly using high-level information at a population and ecosystem level and does not require extensive scientific analysis or information about individual organisms. NRDA, in contrast, compares the impacts of a specific spill in a specific location to specific resources to their unimpacted state. It typically requires an extensive and detailed analysis of information about oil properties, toxicity, distribution, and impacts specific to that individual scenario. It does so without evaluating the alternatives, and usually takes many years to complete. The type and level of detail of information used, the timescale, the purpose of analysis, stakeholder engagement mechanisms, and other factors are very different for NEBA and NRDA and they should not be confused.

4.2.6 Wildlife Rescue and Rehabilitation

Over the past 50 years, the practice of oiled wildlife response has evolved from an activity conducted by small individual nonprofit organizations with minimal external support to a fully integrated part of the overall spill response effort performed in a professional and coordinated manner. In the United States, this progress has corresponded to that seen after the Exxon Valdez oil spill in 1989, with a more ordered and measured response effort as dictated by OPA 90 performed under a structured ICS (see Figure 4.17). While there are some differences in specific protocols and operational activities in active response efforts to different taxa involved (e.g., birds versus marine mammals versus sea turtles), the overall concepts of wildlife rescue and rehabilitation can be applied holistically to all species.

Wildlife response typically falls under the Wildlife Branch within the Operations Section, but works closely with other sections, particularly the environmental unit within the

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Image
FIGURE 4.17 Example organizational chart for U.S.-based marine mammal responses under NOAA’s National Marine Fisheries Service.
NOTE: The Wildlife Branch is a branch of the Operations Section within the larger ICS structure.
SOURCE: Ziccardi et al. (2015).

planning section. Under the guidance of the Wildlife Branch Director (WBD), the main objectives of the Wildlife Branch are typically to:

  • Conduct all operations in such a way that are safe to both people as well as animals;
  • Minimize injuries to wildlife and habitats from the contamination, cleanup effort, and animal recovery operations;
  • Follow legal guidelines when collecting all data, samples, and animals;
  • Document the immediate impacts to wildlife, and report in a timely and complete manner all relevant data and information necessary;
  • Support efforts in spreading information to the media, public, and other interested parties; and
  • Provide the best possible care to affected and/or threatened wildlife.

In general, oiled wildlife response can be divided into three different response strategies: primary, secondary, and tertiary. Primary response tactics include those actions that “keep oil away from wildlife.” The most effective means by which oil is kept from animals is through mechanical, physical, or non-mechanical cleanup (e.g., in situ burning and chemical/biological response). However, reconnaissance of at-risk populations is also critical: both the collection of a priori historical information as well as rapid, real-time reconnaissance of animal presence in (and adjacent to and anticipated [incoming migrations]) the spill area. Additionally, collection of oiled carcasses can be considered a primary response action, as these can act as a risk of oiling (and associated toxicological effects) to scavengers as well as a key component of environmental cleanup actions.

Secondary oil spill response tactics include efforts to “keep wildlife away from oil.” These actions fall into two main categories: deterrence (or hazing) and pre-emptive capture of wildlife. Birds and other animals can be scared away from an oiled area through use of visual or auditory devices, deterred from areas by use of exclusion devices (e.g., fences, netting), or attracted to less risky regions through bait or environmental manipulation. Capture of unoiled,

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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at-risk species (and subsequent handling, transportation, short-term holding, and release of unoiled wildlife) has been done in select incidents, including the relocation of tens of thousands of African penguins during the Treasure oil spill in South Africa and the capture and long-term holding of New Zealand dotterels during the M/V Rena oil spill.

Tertiary response efforts are those typically thought of as the “standard wildlife rehabilitation efforts” during oil spill events (see Figure 4.18). Such recovery and rehabilitation activities are not always undertaken (e.g., in certain situations, recovery and rehabilitation of animals may not likely result in their returning to “normal” after care), but comprehensive assessment for the elimination of animal suffering (often through collection and humane euthanasia) should always be considered even when full-scale response cannot occur. Tertiary response actions fall into several main categories:

  • Capture: During spill events, government agency personnel or trained and experienced wildlife responders from rehabilitation groups capture most oiled wildlife during search and collection efforts. Areas where oiled wildlife are likely to be found must be systematically covered, additionally, responders should accurately record field data (such as date, time, location, and name) as well as start additional legal requirements if required (such as chain of custody procedures).
  • Stabilization: Stabilization and initial first aid (e.g., return to normal body temperature, fluids, and initial brief assessment) should be administered to live oiled animals either in situ if possible, or by being quickly taken to a field stabilization site. At this point, initial triage (or prioritization and sorting of treatment) can be done, including the determination of likelihood of success of rehabilitation and early humane euthanasia using veterinary-approved means when rehabilitation is highly unlikely to be successful.
  • Intake: On arrival at the facility, a standardized intake protocol should be followed, to ensure legal evidence is obtained and documented for possible NRDA injury determination. Each oiled animal should
Image
FIGURE 4.18 Tertiary oiled wildlife response options and activities.
SOURCE: From A Guide to Oiled Wildlife Response Planning, IPIECA Report Series Volume 13.
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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  • be individually identified, a feather sample or fur swab collected for proof of oiling, and a photograph taken. Animals undergo thorough physical examinations based on triaged prioritization (e.g., threatened/endangered status or requiring immediate care going first), noting especially the extent of oiling, and signs of hypothermia, dehydration, and malnutrition. Blood samples are drawn to evaluate, as a minimum, anemia and low serum protein, and all data are recorded in individual records for each oiled animal.
  • Pre-wash care: The washing of oiled birds and heavily furred mammals is a rigorous and stressful process and should not be done on newly admitted animals until they are determined to be physiologically stable. They should only undergo this procedure when they meet certain standard criteria (typically stabilization with warmth, fluids, and nutritive support). Other species (such as pinnipeds aside from fur seals and sea turtles), however, may be able to be cleaned immediately upon intake if blood work and initial exam show no abnormalities beyond physical coating. Animals should be provided nutritional and hydration support (e.g., birds gavage-fed high-calorie nutritional slurries alternating with rehydrating solutions up to eight times daily, with volumes dependent on species, size, and health status) and regularly re-examined to determine when they are medically stable enough to move to cleaning.
  • Cleaning: Standard wash procedures include the use of dishwashing detergent (diluted for birds and furred mammals, full strength in other species) in water heated to, and maintained at, physiologically normal temperatures. This solution is manually agitated around, or massaged into, the oiled pelage, until oil is completely removed. Monitoring of core body temperature and/or close observation of animals for distress should be done at all times. Animals are then rinsed with water heated to physiologically normal temperatures using an adjustable high pressure (40–60 psi) nozzle until all detergent is removed from the feathers or underfur. For heavily furred mammals and birds, it is also recommended that rinse water be 2–5 grains hardness, as minerals in the water will bind with microscopic amounts of detergent and can cause calcium carbonate crystals to form. After animals are completely clean, birds and furred mammals are then allowed to dry using towels, pet groomer dryers, heat lamps, or ambient conditions in their pen, depending on species.
  • Pre-release conditioning: After cleaning, animals should be moved into appropriate enclosures (typically outdoor pools, aviaries, or pens) that are of sufficient size to allow accurate determination of behavior, feeding habits, and waterproofing status. Pen and water quality must be excellent to prevent recontamination of feathers/fur by oily feces and fish, and animals should be continually observed for signs of inadequate waterproofing. Excellent nutritional support should be provided, and regular medical and waterproofing checks should be done to plot progress. Once animals meet established release criteria (usually, at a minimum, normal behavior, good body weight, waterproof, and normal physical exam, hematology, and serum chemistry values), they can be marked with a permanent tag, metal leg band, or other means of post-release monitoring, and released into an appropriate clean environment.

Since the release of Oil in the Sea III, numerous advances in oiled wildlife rehabilitation have occurred, both at a systemic level and a scientific level. Internationally, the importance of oiled wildlife efforts as an integral part of overall spill response has been recognized, particularly after the DWH incident in 2010. The International Petroleum Industry Environmental Conservation Association (IPIECA)-International Association of Oil and Gas Producers (IPIECA-IOGP) Oil Spill Response Joint Industry Project (OSR-JIP) recognized oiled wildlife response involving specialist personnel as one of the 15 key capabilities necessary for effective preparedness and response. In 2015, as part of Phase 2 of the OSR-JIP effort, an ambitious wildlife response preparedness project was initiated. This Global Oiled Wildlife Response System (GOWRS) project, which involved 11 leading wildlife response organizations from seven countries (including four leading organizations from the United States), aimed to develop an international framework for oiled wildlife response as well as encourage the further development of wildlife response preparedness by industry and other stakeholders. This effort has led to the development of numerous globally acceptable planning and response documents; animal care standards; a system of readiness and response encompassing training; equipment, and personnel readiness; and a source for the best available information on effective planning needs (IPIECA, 2014, 2017; Ziccardi, 2021).

In the United States, as a consequence of the DWH incident, NOAA’s National Marine Fisheries Service embarked on a significant effort to establish national protocols and procedures for cetaceans, pinnipeds, and sea turtles to support both integrated response efforts, but also better organization of NRDA efforts (NOAA, 2015). This national effort has also led to specific efforts in key regions of the United States, with Arctic, Gulf of Mexico, and Pacific Island regional plans being developed to focus on key risk issues in those sensitive habitats. On the scientific front, many investigational and laboratory studies following DWH focused on attempting to better understand the overarching effects of oil on wildlife (see Chapter 6), and these have led to significant advances in how to better collect and care for animals and are now being more fully incorporated into the medical protocols of all professional oiled wildlife response organizations.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Probably the most contentious issue surrounding the recovery and rehabilitation of oiled wildlife is whether the effort is a waste of resources focused on individual animals (versus populations), whether survival of rehabilitated animals is poor, and whether the resources expended on such would benefit wildlife more if directed to other conservation efforts (Estes, 1998; Jessup, 1998). There is considerable variability among post-release survival studies in the literature, dependent on species differences, characteristics of the spill including product spilled and speed of response, or specifics of rehabilitation methods (summarized in Henkel and Ziccardi, 2018). However, despite this variation, more recent cases have clearly shown survival far in excess of estimates generated prior to 1993 (as detailed in Sharp, 1996), and in several studies the survival of rehabilitated and control animals showed no discernable differences (Golightly et al., 2002). Recent studies have also shown that rehabilitated oiled wildlife can successfully re-enter the breeding population and reproduce (Whittington, 1999; Sievwright, 2014).

In summary, wildlife rescue and rehabilitation can be a highly successful operational effort during oil spills—one of the most positive, publically visible outcomes of such emergencies. To achieve high release rates and best possible post-release recovery rates, robust planning for oil spill response is critical, as is conducting ongoing research into, and incorporating the results from, the latest and best available science in protocols for veterinary care and rehabilitation. Only with this focus on readiness and applying “lessons learned” can rapid capture and best achievable care of oil-affected wildlife be realized.

4.3 CONCLUSIONS AND RESEARCH NEEDS

Conclusion—Source Control: Second only to prevention, an effective source control is the key strategy that can reduce the volume of hydrocarbons entering the marine environment as well as its potential environmental and socioeconomic impacts. Advanced source control measures have been developed for wells, pipelines, and vessel salvage. The use of proven source control techniques continues to reduce potential hydrocarbon volumes that may enter North American waters, and their continuous advancements should be enabled through research and development efforts.

Conclusion—Incident Command System: The value of the Incident Command System (ICS) in effective incident management, integrating interests of diverse groups of stakeholders, and ensuring effective coordination and deployment of response resources to maximize protection of human health and safety as well as resources at risk has been documented since its adoption.

Conclusion—Response Toolbox: No single response technique is effective under every environmental condition and every spill scenario. They each have their advantages, challenges, and optimal operational conditions for use. Greatest effectiveness of response activities is achieved when various response techniques are available (a response toolbox concept) and their use is tailored to a specific response scenario based on safety, effectiveness, ability to protect environmental and socioeconomic resources and facilitate fastest recovery to the pre-spill conditions. If required, the NEBA tools and processes (CERA, SIMA, and CRA) are available to compare oil spill response options and select an optimal combination of activities that could result in maximum protection of environmental, socioeconomic, and indigenous resources at risk.

There are some barriers that may challenge the integration of best available science and new technologies as well as utilization of available response techniques and monitoring tools in spill response. Some of these barriers include inability to conduct full-scale field tests with real oil in the United States and significant challenges with conducting them in Canada, which prevents verification and optimization of new response technologies in the field and gathering of field-scale scientific information; challenges with commercialization and regulatory approvals of new technologies; insufficient knowledge of decision-makers and stakeholders of best available techniques and practices; extended time required to make decisions at the time of response; communication challenges of response details and decision-making process with interested stakeholders; and much more. Joint education and outreach efforts are needed from the agencies and industry to increase understanding and acceptance of these tools among specialists and the general public, as well as to facilitate involvement of local and indigenous representatives.

Conclusion—Funding for Oil Spill Research: Significant progress has been made in advancing response techniques since Oil in the Sea III. There are a number of standing research programs as well as focused multi-year, multidisciplinary research programs with a fixed timeline for funding. All of these programs have generated invaluable advances in oil spill response knowledge and technologies. Continuous investment into oil spill research and development and deployment of verified technologies in the field should be encouraged.

Conclusion—Extrapolation of Research Results: Researchers who clearly indicate response scenarios/conditions being simulated during laboratory, test tank or modeling experiments, and explain the process for extrapolation of the results into field conditions, enhance the relevance of their work and make it easier to integrate their findings into real-life responses. This allows for a better comparison between different studies and eases their integration into the response decision-making. Great caution is advised in extrapolating conclusions from smaller-scale experiments to field conditions when the optimal process for doing so is not suggested by the researchers.

Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Conclusion—Field Experiments: It is not possible to simulate all the complexities and variability of field conditions in even the largest test tanks. Field experiments with real oil and spill-treating agents and studies conducted during actual response events are critical for the development, testing, and improvement of response techniques under realistic conditions.

Conclusion—Remote Sensing, Monitoring, Modeling and Other Information/Computation-Related Technologies: Since the Oil in the Sea III report, significant progress has been made in spill modeling, monitoring, remote-sensing, big data collection and processing, and other information/computation-related technologies. These techniques have become an integral part of the response and natural resource damage assessment activities. Their progress and advancements are expected to continue at a fast pace in the coming years. Further progress and adoption of relevant and verified technologies will improve response effectiveness.

Conclusion—New Fuel Types: New requirements for low sulfur fuel oils (LSFOs) for marine shipping came into effect in 2020 but studies on these oils, which have properties that are combinations of light distillates and heavier distillates, are currently extremely limited. The few very low and ultra-low (VLSFO and ULSFO) samples studied to date differ chemically from traditional marine fuel oils and from each other. Their fate and behavior are also likely to be different, including a potential to become semi-solid under some circumstances. The semi-solid state of a slick can significantly limit the effectiveness of available response options and require special response strategies.

Conclusion—Health and Safety Risks to Response Professionals: Protection of the health and safety of the general public as well as responders is the primary priority during emergency response. Numerous best practices for safe operations and use of personal protective equipment by responders have been developed, implemented in the field, and integrated in the incident management processes. Still, response operations, especially those involving mechanical recovery and shoreline cleanup where responders have to remain in close proximity to the oil, as well as operations involving heavy equipment under offshore conditions, have inherent risks.

RESEARCH NEEDS

Continued research, technology development, and implementation efforts aimed at prevention of spills, early detection, and limitation of spill volume if a spill occurrs is encouraged. More specifically, the research included in Table 4.5 would benefit future oil spill response efforts.

TABLE 4.5 Research Recommended to Advance Oil Spill Response and Minimize Effects

4.1 New Fuel Types and Oilfield Production Products: The effectiveness of various response techniques and their windows of opportunity in responding to hybrid fuel oil, particularly low sulfur fuel oils, and to diluted bitumen (“dilbit”) oilfield products, must be carefully evaluated.
4.2 Lifecycle Analysis of Oil Spill Based on Response Scenarios: A continuous collaboration among academic, government, and industry scientists and response practitioners is needed to develop a comprehensive, multifaceted, and realistic analysis of “cradle to grave” oil slick fate and effects for various response scenarios, including monitored natural attenuation. This analysis should include all possible variations of response scenarios of a single event so as to give decision-makers a complete and comprehensive picture of the decision outcomes in each of the scenarios. At present, it is challenging to create a complete and comprehensive picture from the results of multiple uncoordinated studies with a narrow focus, as these studies are conducted with different goals and conditions in mind and do not lend themselves to a seamless integration.
4.3 Health and Safety Risks to Response Professionals: Research into health risks and psychological impacts to response personnel involved in various types of response operations should be conducted. This information should be integrated into response decision-making.
4.4 Response Tools—Mechanical Recovery: Mechanical recovery technologies would benefit from the research efforts aimed at improving encounter rates, specifically the volume of oil entering the containment devices and available for recovery as well as optimization of a particular technology’s efficiency under various environmental conditions and spill scenarios (e.g., recovery of submerged oil). Mechanical recovery should also be viewed as a multicomponent system involving equipment mobilization, oil collection, recovery, storage, transfer, and disposal. Analysis of potential bottlenecks in this system under different response scenarios will help to identify potential areas for improvements.
4.5 Response Tools—In Situ Burning: Research focused on improving efficiency of and expanding a window of opportunity for in situ burning should continue and include various scenarios. Such scenarios could include burning in conventional booms, use of herders, inland burning, and burning under Arctic conditions.
4.6 Response Tools—Chemical Dispersants: Continuous research efforts focused on increasing natural dispersion processes through use of chemical dispersants (including new formulations and natural materials), and on mechanical dispersion techniques for selected offshore blowout scenarios are recommended.
4.7 Response Tools—Arctic Conditions: Although significant progress has been made in our understanding of the applicability and efficiency of various response techniques under Arctic conditions, these efforts should continue, given the great diversity of potential response scenarios as well as new formulations of fuels that may be encountered in that region.
4.8 Oiled Wildlife Management: Additional research into long-term impacts, survival rates, and return to normal function of treated and released animals would be beneficial to refine oiled wildlife management methods.
Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Suggested Citation:"4 Accidental Spill Mitigation." National Academies of Sciences, Engineering, and Medicine. 2022. Oil in the Sea IV: Inputs, Fates, and Effects. Washington, DC: The National Academies Press. doi: 10.17226/26410.
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Oil in the Sea IV: Inputs, Fates, and Effects Get This Book
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Oil and natural gas represent more than 50 percent of the worldwide energy supply, with high energy demand driven by population growth and improving standards of living. Despite significant progress in reducing the amount of oil in the sea from consumption, exploration, transportation, and production, risks remain. This report, the fourth in a series, documents the current state-of-knowledge on inputs, fates and effects of oil in the sea, reflecting almost 20 additional years of research, including long-term effects from spills such as the Exxon Valdez and a decade-long boom in oil spill science research following the Deepwater Horizon oil spill.

The report finds that land-based sources of oil are the biggest input of oil to the sea, far outweighing other sources, and it also notes that the effects of chronic inputs on the marine environment, such as land-based runoff, are very different than that from an acute input, such as a spill. Steps to prevent chronic land-based oil inputs include reducing gasoline vehicle usage, improving fuel efficiency, increasing usage of electric vehicles, replacing older vehicles. The report identifies research gaps and provides specific recommendations aimed at preventing future accidental spills and ensuring oil spill responders are equipped with the best response tools and information to limit oil’s impact on the marine environment.

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