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6 COMPARING RESPONSE OPTIONS
Pages 165-198

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From page 165...
... This diversity challenges responders to be adaptive to the particular circumstances of a spill and has led to the development of multiple marine oil spill response options. Current commonly used, open-water response methods include mechanical recovery of oil using skimmers and booms; in situ burning of oil at the surface; monitored natural attenuation; and enhanced dispersion of oil through the application of dispersants, either at the surface or via subsea injection.
From page 166...
... 166 THE USE OF DISPERSANTS IN MARINE OIL SPILL RESPONSE TABLE 6.1  Operational Summary of Open Water Response Options Response Option Benefits Limitations Surface • High aerial coverage rate possible at the • Special approvals required Dispersant water surface • May not work in calm seas Application • Large volumes of oil can be treated • Light and water depth limitations • Reduced vapors at the water surface; • Short-term, localized increase in toxicity improves workers' safety • Potential impact on water column resources • No recovered oil storage requirements • Specialized equipment and expertise • Lower manpower requirements required • Reduces the potential for oil reaching the • May not be as effective on high viscosity shoreline fuel oils • Enhances natural biodegradation • Has a limited "window of opportunity" for • Useful in higher wind and sea conditions use • Effective over wide range of oil types and • Relies on biodegradation to remove oil conditions from the ecosystem • Public perception Subsea • Large volumes of oil can be treated with • Less known about long-term effects of Dispersant high efficiency subsea use Injection • Lower dispersant-to-oil ratios can be used • Potential impact on water column resources • Reduced vapors at the water surface; • Localized increase in toxicity and reduction improves safety in oxygen • Oil dispersed through a larger portion of • Special approvals required the water column • Specialized equipment and expertise • Lower manpower requirements required • Reduces the potential for oil reaching the • It is difficult to monitor dispersant shoreline effectiveness • Useful in wind and sea conditions that • Relies on biodegradation to remove oil would inhibit other response options from the ecosystem • Effective over wide range of oil types and • Public perception conditions • Applications can be performed continuously -- 24 hours, 7 days per week At-Sea • Permanently removes oil from the water • Inefficient and impractical on thin slicks Mechanical • Well-accepted, no special approvals needed • Is limited by weather, sea state, and light Recovery • Effective for recovery over wide range of • Requires storage capability spilled products • Typically recovers no more than 10% of • Large "window of opportunity" the oil spilled in open ocean environments, • Greatest availability of equipment and more may be recovered in other conditions expertise • Labor and equipment intensive • Recovered product may be reprocessed • Large volumes of oily waste Controlled In • High oil elimination rate possible • Requires fresh oil with volatile components Situ Burning • No recovered oil storage requirements • Special approvals and permits required • Effective over wide range of oil types and • Ineffective in inclement weather or high conditions sea state • Black smoke perceived as significant impact on people and the atmosphere • Localized reduction of air quality • Specialized equipment and expertise required • Burn residue may sink or be difficult to recover
From page 167...
... An International Union for Conservation of Nature report on evaluating oil spill response highlights the importance of considering the resources to be protected, the effectiveness of different response options, and the possible impacts of the response itself (Stevens and Aurand, 2008)
From page 168...
... BOX 6.1 Concentrations of Dispersed Oil After Dispersant Use Previous studies and spills have demonstrated that, for surface dispersant operations, dispersed oil concentrations generally range from 10-50 ppm in the top few meters of the water column for the first hour following dispersant application. Rapid horizontal and vertical mixing then quickly reduces the con centration of dispersed oil to below 1 ppm.
From page 169...
... by measurement of fluorescence of specific crude oil components or laser light scattering from dispersed oil droplets should be used to augment visual observations. A number of laboratories have evaluated dispersant effectiveness using a variety of test methods with known amounts of dispersant, reference oil, and water in an enclosed vessel under known energy mixing rates (Venosa et al., 2002)
From page 170...
... SUBSEA DISPERSANT INJECTION (SSDI) Overview The response to the 2010 DWH oil spill is the first case where dispersants were applied at the wellhead on the seafloor.
From page 171...
... SOURCE: Oil Spill Response Limited Subsea Well Intervention Services. hydrocarbon biodegradation at depth; decreased atmospheric volatile organic compound (VOC)
From page 172...
... benthic organisms. In general, there is less known about the biota at depth to judge the potential impacts of dispersed oil on the ecosystem.
From page 173...
... . A number of lessons were learned from the extended use during the response, and projects have been undertaken to • Better understand factors that influence dispersed oil droplet size -- for example, dispersant type, DOR, oil type, and mixing energy (Brandvik et al., 2013, 2014a,b, 2018, 2019a,b)
From page 174...
... Finally, skimmer system configurations may need to change as the oil becomes more weathered, which can result in response delays. Effectiveness Mechanical recovery in the offshore environment is affected by weather conditions, the extent of oil weathering, and the actual encounter rate.
From page 175...
... Benefits ISB can be highly effective at permanently removing encountered oil from the water and reduces the total volume of oil that would need to be collected and disposed. Because most crude oils will burn, ISB can be an effective technique for a wide range of oil spills.
From page 176...
... The fate of the oil is generally monitored to determine both if it is attenuating as predicted and if an active response is necessary. Benefits Natural attenuation may be appropriate in cases where offshore spills do not threaten shorelines, sensitive habitats, and protected species, or when high sea states exist and natural dispersion is expected to prevail and other response options may not be safely deployed (e.g., during winter months and storm events)
From page 177...
... For offshore slicks, natural attenuation could lead to the presence of oil slicks on the water surface for an extended period of time; for example, hours for light oils during energetic sea states or weeks to months for heavier or emulsified oils during calm sea states. Active monitoring of the area that may be affected by a spill is required because changes in winds and currents may later move the oil into an area where response is necessary.
From page 178...
... . In particular, following the DWH oil spill, industry established a Global Dispersant Stockpile (GDS)
From page 179...
... , Singapore, Trinidad, United States NOTE: Correct at the time of publication. SOURCE: Oil Spill Response Limited.
From page 180...
... 180 THE USE OF DISPERSANTS IN MARINE OIL SPILL RESPONSE FIGURE 6.4  Example framework for dispersant use approval.
From page 181...
... It is also often associated with extreme cold that further inhibits response options. At the same time, these same conditions reduce oil weathering, allowing burning and dispersants to be effective over a longer
From page 182...
... as well as numerous research projects and programs (e.g., BSEE Arctic Oil Spill Response Research, Oil in Ice Joint Industry Program, and Arctic Response Technology JIP)
From page 183...
... Treatment of uncertainty is largely dependent on first establishing equivalencies in the risk assessments to be compared. For example, CRAs employed to quantify and compare human health risks using the disability-adjusted life year start with the same foundational datasets on life FIGURE 6.6  Hypothetical modeling results of oil spill damage estimates associated with use of subsea dispersant injection (SSDI)
From page 184...
... In the ensuing years, the sites continued to display differences in recovery, and there is a clear demonstration that exposure to dispersed oil was less disruptive overall to the marine and intertidal communities. While the water column species were exposed to higher levels of hydrocarbon during the initial and relatively severe conditions of the experiment, long-term health of the ecosystem was more affected by the impacts to the mangroves, and a neutral comparison of the ecosystem components would favor a decision to use dispersants.
From page 185...
... SOURCE: Baca et al., 2014. CRA SSDI Studies Recent advances in numerical modeling have allowed the examination of the potential impacts of the application of dispersants and other response options through the use of the CRA tool.
From page 186...
... , but the risk assessments resulting from the CRA-1 have not been. That said, when an integrated model is used to compare various response options, many model uncertainties may tend to cancel each other, making the relative prediction more accurate than an absolute prediction.
From page 187...
... more than any of the other responses did. However, SSDI substantially increased the volume of hydrocarbons in the water column, most of it at the plume trapping depth located at roughly 300 m above the seafloor.
From page 188...
... A "cost" would be an increase in subsurface oil. Figure 6.9 shows that the fates benefits of small droplets start to accrue when the median droplet size (d50)
From page 189...
... at any time during the 66-day simulation versus droplet size for the Extended CRA runs (French-McCay et al., 2018b)
From page 190...
... . The gradated blue rectangular areas denote the flow rates where net fates benefits will result: that is, the d50 is less than the critical droplet size for that water depth.
From page 191...
... . The gradated background serves as a reminder that fates benefits rapidly increase as the droplet size decreases beneath the critical droplet size.
From page 192...
... . Once the model was validated, they used it to estimate the distribution of oil through the water column during DWH.
From page 193...
... (2013, 2014a) on Macondo-like oil has shown that a DOR of 1:100 to 1:50 is probably optimal for a subsurface oil spill and would result in a droplet reduction of three times more than that observed with a DOR of 1:250.
From page 194...
... Total 13 23 23 48 58 b Based on the top 100 m of the water column, as described in the modeling results. cSurface dispersant only for days 2-9; surface and subsea dispersants for days 10-30.
From page 195...
... the depth of ~20 m. Fish eggs/larvae Fish Marine Mammals Plankton Sea Turtles Vegetation Water Column (deeper: The marine pelagic environment from the oceanic mixed layer (~20 Birds (Diving)
From page 196...
... Fish eggs/larvae Fish Marine Mammals Plankton Sea Turtles Water Column (deep: The marine pelagic environment from the oceanic mixed layer (~20 Birds (diving) greater than 20 m)
From page 197...
... FINDINGS AND RECOMMENDATIONS Finding: Each response method has a complex suite of advantages and disadvantages, including and not limited to encounter rate, effectiveness, and ecosystem and human health effects, that are considered when selecting response options. Finding: Experience with historical spills and integrated models consistently indicate that for large spills, dispersants (both subsea dispersant injection [SSDI]
From page 198...
... The use of integrated models in the new SIMA and CRA tools provides a mechanism for assessing "combinations of response options deployed simultaneously," with particular focus on large-volume events, which is a considerable improvement over the Consensus Ecological Risk Assessment method, which is limited to a single response option at a time. Recommendation: Ensure that the decision-making tools consistently and adequately address uncertainty in estimates of potential human health issues as well as environmental impacts.


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