OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills

OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills OIL SPILL SCIENCE chapter 16 – a practical guide to chemical dispersion for oil spills

Chapter 16 A Practical Guide to Chemical Dispersion for Oil Spills Merv Fingas Chapter Outline 16.1 Introduction and 583 Decision Making 16.2 How Dispersants 591 Are Used 16.3 Safety and 598 Postdispersion Actions Appendix A Specific Spill Scenarios and Dispersion Strategies Appendix B Nomograms to Calculate Spreading and Viscosity with Time 603 605 16.1 INTRODUCTION AND DECISION MAKING Dispersants are recognized as an alternative countermeasure for controlling oil spills on water When used properly, with certain oils, and under the right conditions, chemical dispersants can rapidly reduce the oil on the surface or divert surface oil from following undesirable trajectories Chemical dispersion can shorten the response time to an oil spill, thus reducing the chances that the oil will move further on the water surface and thereby protecting sensitive areas Rapid dispersion of oil can prevent the oil from reaching shorelines, which are difficult to clean and where the greatest environmental damage caused by oil spills occurs Dispersants are surfactant formulations that create small oil droplets that move into the water column They are applied to achieve an approximate dispersant-to-oil ratio of 1:15 to 1:25, although slick thickness is hard to judge and no measurement technique is available Although boats and ships have historically been used for this purpose, their ability to treat large areas is very restricted Today, dispersants are usually applied from low-flying aircraft Spray units have been designed for many platforms and are available as either permanent or temporary installations on whatever platform is available As Oil Spill Science and Technology DOI: 10.1016/B978-1-85617-943-0.10016-4 Copyright Ó 2011 Elsevier Inc All rights reserved 583 584 PART | VI Treating Agents dispersants are applied undiluted from aircraft and are usually diluted with seawater when sprayed from boats, quite different equipment is required for the two application platforms Effectiveness is a primary concern when using dispersants It has been found that their effectiveness depends primarily on the type of oil being dispersed and then on the amount of sea energy at the time of the dispersal operation The primary factor affecting the ability of an oil to disperse is its composition The lighter the oil, the better it disperses Heavier components such as resins, asphaltenes, and waxes not disperse Heavy residual oils such as Bunker C, which consist mostly of these heavier components, disperse little, if at all A minimum of sea energy is required before dispersants function The higher the sea energy, the more effective is the dispersant As oil weathers, its more dispersible content decreases and its viscosity increases, making it more difficult for the dispersants to mix with the oil Heavy oils and highly weathered oils may not disperse at all under certain conditions Light oils will disperse well and, if left untreated, may also disperse naturally It is important to recognize that not all oil that is treated will disperse; there will always be some residual slick This certainly must be weighed in considering response options It is also very important to recognize that the dispersants are a temporary measure Much of the oil dispersed will resurface within 12 hours Thus if the trajectory of the surface slick is the same as the subsurface slick, the overall benefits of dispersant treatment will be nullified The use of dispersants is a trade-off between a number of factors, such as protecting shorelines and birds versus possibly adversely affecting fish In most countries, the use of dispersants is tightly regulated by government agencies The decision process involves assessing the current situation and the protection priorities such as fish, shoreline types, and special habitats Other factors that must be assessed include the probable effectiveness of the dispersant on the type of oil spilled, the temperature and salinity of the waters, and the ability to disperse significant amounts of oil with the equipment and dispersant available The steps involved in chemical dispersion are shown in Figure 16.1 How dispersion decision making proceeds is outlined in Figure 16.2 These figures will be highlighted in the discussion that follows 16.1.1 An OverviewdHow, When, and Where Dispersants Are Used Dispersants are considered an alternative countermeasure for oil spills, along with the many other countermeasures available Often, several countermeasures should be applied at one time Dispersants are a control tool and not remove oil from the environment Thus they are used when oil spills are approaching sensitive areas that require quick protection When considering the use of dispersants, the proximity of the dispersant application to sensitive Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills Oil spill occurs 585 Sensitive areas would benefit Oil is dispersible Chemical chosen as a response option Sea energy is sufficient Plans are in place Equipment is obtainable Obtain regulatory approvals Choose targets Dispersant Spray equipment Set operation Target sites Weather/time windows Implement equipment deployment plans Protection priorities Implement health and safety plans Brief all personnel on deployment and health and safety plans Transport supplies and personnel Begin dispersant operation Monitor dispersant operation Conclude operation Return equipment Assess and report results FIGURE 16.1 Steps in chemical dispersion marine environments, such as mangrove forests, sea grasses, marshes, and corals, is an important factor Decisions about the use of dispersants must be based on a net environmental benefit analysis of use versus nonuse of dispersants as discussed in Section 16.1.2 The potential environmental impact of the trajectory of the dispersed oil plume should be considered in addition to the environmental impact of the undispersed oil plume 586 PART | VI Treating Agents Yes Yes No wind 1mm , and viscosity < 5000 mPa.s No Begin the implementation of the dispersant operation according to plan FIGURE 16.2 Decision flowchart for chemical dispersion Many jurisdictions impose regulatory limitations on the water depth to which dispersants can be applied (3 to 30 m) Dispersants are best applied in deep waters and not close to sensitive resources Applying dispersants to prevent oil from entering the sensitive habitats should be considered to minimize environmental impact Dispersants should not be used, however, to remove oil Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 587 adhering to mangroves or shorelines Instead, shoreline cleaners or surfacewashing agents should be considered It is important to carry out the preplanning noted in this document before applying dispersants The following are the minimum conditions that should be met when using dispersants: Fundamental conditions a) There must be a positive potential benefit to using dispersants b) There must not be sensitive environments that could be impacted c) The operation should be feasible, with enough equipment and dispersant to produce a beneficial result d) The oil should be dispersible and in dispersible condition, for example, not highly weathered or in the form of a stable emulsion e) The oil should be heading toward an area or environmental habitat that needs to be protected f) The water should be of sufficient salinity (>25%) to allow for effective dispersion g) The effectiveness should be considered, as well as the effects of the remaining oil on the surface, which will always be present h) The inevitable resurfacing of the dispersed oil must also be considered Environmental considerations a) The habitat in which dispersion will occur is not sensitive to hydrocarbons in the water column b) The dispersed oil plume will not come into contact with sensitive water environments, including coral reefs and beds of sea grass, within the next 12 hours c) The dispersion will result in a net environmental benefit as described in Section 16.1.2 Dispersants are generally applied when the above conditions exist They are applied directly to the oil using application equipment either from boats, ships, aircraft, or helicopter buckets Plans for the application must be developed in advance to ensure safety and the efficiency/effectiveness of the operation The items to be considered in this preplanning stage are listed in Table 16.1 16.1.2 Net Environmental Benefit Analysis A Net Environmental Benefit Analysis or NEBA is used to evaluate the decision to use oil spill dispersants The concept is that the total benefit of applying dispersants is evaluated compared to the potential damage that would occur if they were not applied It is important to stress that at this time NEBA is more of a concept than a developed tool The NEEBA, or Net Environmental and Economics Benefit Analysis, is a variation on this theme and adds the concept of economics to the vector It should be stressed that this concept has been even less developed as a tool than the basic NEBA 588 PART | VI Treating Agents TABLE 16.1 Preplanning for Dispersant Application Environmental Resources Sensitivity mapping coral reefs mangroves shallow areas endangered species species at risk Oil Types Tests with oil types Effectiveness scenarios Weathering profiles Time windows Dispersants and Equipment Dispersant stocks Equipment for this Dispersion planning Dispersion scenarios Preplanning Preplanned NEBA Preplanned conditions The sequence of analysis is intended to proceed from the concentrations of oil expected under the slick, the toxicity of these diluted fractions to the local flora and fauna, and a comparison of this with the distribution and fate of the oil if not treated It is currently proposed that models be used to generate this type of information and sometimes even the economic analysis that flows with it The following is the scenario for a full NEBA/NEEBA analysis Generate the dispersant application and countermeasures scenarios This is typically carried out using computer analysis and includes: l Spread, thickness, and geographical prediction of oil deposition, including weathering and chemical composition; l Application scenario, including dosage of the various amounts, prediction of effectiveness, and deposition of unburned fractions; l Very importantlydconcentrations of the oil under the slicks and their fate and movement; l Effectiveness of mechanical and other countermeasure scenarios; and deposition and movement of the oil if no countermeasures were carried out A NEEBA analysis would include the economics of the three componentsd dispersant application, no-countermeasures, and the normal mechanical removal efforts The dilution of dissolved and dispersed hydrocarbons can be calculated Dispersant scenarios should be calculated with the variances in the dispersibility of the oil It is typical to calculate all the dispersant scenarios, with effectiveness half of the predicted amount and some percentage above to yield three scenarios Generate ecological-impact scenarios for mechanical countermeasures only, other forms of countermeasures that may be considered or applieddin suites or separatelyddispersant-only, and no countermeasures Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 589 Again, economics can be included to yield a cost analysis The impact scenarios will include the toxic effects on key species in the affected areas, the variances in trajectories, and a sensitivity analysis of the predicted oil concentrations under the slick The predicted recovery of species is also modeled The outputs of the total process include information on the effects for each countermeasure scenario, including the effects of undispersed oil or oil that was not subject to the dispersant process These effects can then be evaluated in terms of their ecological value The social costs and benefits are also evaluated at this stage A NEEBA analysis would include an evaluation of the economic costs and the benefits of each countermeasure scenario The sequence of NEBA planning is listed in Table 16.2 16.1.3 Scenarios For Which Dispersants Might Be Used It is important that scenarios for dispersant application be developed for the regions of concern Typical scenarios for situations in which dispersants might be used are listed in Appendix A 16.1.4 Planning Process and Checklists Planning begins with assessing the environmental resources in the area as listed in Table 16.1 After the sensitive areas are mapped, focus is then on the available dispersants and application equipment, which will dictate the capability to chemically disperse oil slicks If the equipment is available, planning then proceeds to scenarios such as illustrated in Appendix A This is tied together with the NEBA analysis as summarized in Table 16.2 It is important to set the priorities for chemical dispersion in line with the priorities for environmental protection Planning then continues with examination of the oil types that may require dispersion in the region Effectiveness scenarios are set for the oils, along with the weathering profiles, and the resulting time windows for effective chemical dispersion This is readily accomplished by referring to Appendix B This appendix provides tables and nomograms that give values or estimations of the spreading area, thickness, oil viscosity, dispersant needed, and the hours of operation for several dispersant application platforms for 100, 1000, and 10,000 ton scenarios and for 12, 24, and 48 hours The final step is to compile all the information into preplanned NEBA and preplanned scenarios so that decisions can be made quickly Oil spilled on water undergoes several changes with time, and this should be taken into account when planning dispersant operations The processes that cause these changes include emulsification, evaporation, oxidation, spreading, and natural dispersion In order to determine the effectiveness of a dispersant 590 PART | VI Treating Agents TABLE 16.2 Sequence of Analysis in NEBA Sequence Number Information Input Analysis Output Basic spill information Trajectory modelling Direction of surface slick Amount Fate modelling Direction of plume/ dispersed oil Dispersant available Dispersant modelling Dispersed oil concentrations Dispersant operation information Countermeasure modelling Amount dispersed Area resources Effects modelling Effect of dispersed/ undispersed oil NEBA NEBA Total effects of dispersed oil Location Oil type Weather and predicted weather Oceanographic information Undispersed oil and residual oil Economic model Social analysis Social costs and benefits of each scenario NEEBA Costs of alternatives operation for a particular oil slick, it is important to understand how these processes change the properties of spilled oil and ultimately affect the oil’s ability to disperse As time progresses, the slick becomes increasingly thinner on the water A light crude oil will be an average of 0.5 mm thinner after about 48 hours, a thickness that is nearly impossible to treat with dispersants For practical purposes, mm will be taken as the practical limit in this guide Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 591 The formation of emulsions significantly changes the properties and characteristics of oil spills Stable emulsions contain from 60 to 80% water, thus expanding the original volume of spilled material by two to five times Most significantly, the dynamic viscosity of the oil typically changes from a few hundred mPa.s to about 100,000 mPa.s, a typical increase of 1000 A liquid product is thus changed to a heavy, semisolid material For practical purposes, once an emulsion has formed, the oil is considered to be nondispersible 16.2 HOW DISPERSANTS ARE USED The primary method for applying dispersants is to spray the dispersant onto the slick as soon as possible after the spill The dispersant must be applied onto slicks before they become too thin and before the oil weathers excessively Studies have been done on the application of dispersants directly into leaking tanks This has been largely abandoned because analysis of case histories shows that very little opportunity for such application actually exists Furthermore, implementing such a method with a stricken tanker would probably be more difficult than to conduct a spray operation Dispersants were first applied on oil spills using boat-mounted spray systems In the early 1970s, it was realized that small boats with a spray width of about 10 m could not deal with a very large amount of oil Both large systems for larger boats or small shipsdthe size of supply boatsdand spray systems for aircraft were developed Smaller vessels are rarely used today for application While there are spray systems for applying pesticides, spray systems for dispersants must be designed quite differently as spray volume is generally 10 to 50 times greater Most pesticide systems are designed to apply pesticide as a fine spray or mist with droplet sizes from about 50 to 200 mm, whereas dispersants are best applied at 400 to 700 mm These droplets are large enough to result in good deposition rather than being blown away and small enough that the dispersant droplets not break through the oil slick The physics of the system is such that dispersants must be diluted in order to be sprayed from a slow-moving ship, whereas they are applied “neat” from aircraft Applying dispersants in neat form is thought to be best because, when diluted with water, dispersants may not repartition to the oil phase and could be lost to the water column Mixing seawater on vessels requires apportioning pumps or devices to ensure a consistent mixture of oil and water There are several practical references and standards on the design and calibration of such systems The advantage of aerial spray systems is that, in theory, they can cover a large area A concern is that of the desired droplet size All past work was based on the premise that a 400 to 700 mm droplet size was best for deposition The effect of droplets in this size range on spills has not been determined Spills spread rapidly and are often at this size range or thinner within hours It is known that slicks will often spread down to a 100 mm (0.1 mm) thickness 592 PART | VI Treating Agents within hours Researchers at earlier aerial trials have suggested that the mean droplet diameter should be about half of the slick thickness 16.2.1 Dispersion Spray Equipment Dispersants are best applied either “neat” (undiluted or diluted with water) Aerial spraying, which is done from small and large fixed-wing aircraft, as well as from helicopters, is the most popular application method Spray systems on small aircraft used to spray pesticides on crops can be modified to spray dispersants Such aircraft can carry about 250 to 1000 L of dispersant and can perform many flights in one day in diverse conditions Some spray systems and their aerial coverages are listed in Table B2 in Appendix B As can be seen in the table, large spray systems on large aircraft are attractive from the aerial coverage point of view Spray systems are available for boats, which vary in size from 10‑ to 30‑mwide spray booms to tanks from 1000 to 10,000 L As dispersant is almost always diluted with seawater to maintain a proper flow through the nozzle, extra equipment is required on the vessel to control dilution and application rates About 10,000 to 100,000 L of dispersant can be applied in a day, which would cover an area of million m2 or km2 As this is substantially less than could be sprayed from a single aircraft, spray boats are rarely used for a large spill A spray system operating from a vessel is shown in Figure 16.3 When spraying dispersant, it is important to deliver fine droplets (400 to 700 Fm) to the slick at sufficient dosage to produce results The dispersant-to-oil ratio is generally taken to range from 1:15 to 1:25 It is also essential to ensure that the dispersant comes into direct contact with the oil Droplets larger than 1000 Fm will break through the oil slick and cause the oil to collect in small ribbons, which is referred to as herding This can be detected by the rapid clearance of the oil in the dispersant drop zone without the formation of the usual white-to-coffee-colored plume in the water column This is very FIGURE 16.3 A spray system from a boat in operation (note the underlapping spray pattern) 596 PART | VI Treating Agents 16.2.4 Monitoring, Sampling, and Analytical Equipment The purpose of monitoring protocols is first to determine whether or not dispersant applications are effective and second to estimate their relative effectiveness Dispersant effectiveness is defined as the amount of oil that the dispersant puts into the water column compared to the amount of oil that was spilled In the field, effectiveness is visually indicated by the formation of a yellow-to-coffee-colored plume of dispersed oil in the water column which may be visible from ships and aircraft This is shown in Figure 16.7 Dispersant effectiveness is primarily monitored by visual surveillance or insitu measurements of oil concentrations When testing dispersant effectiveness in the field, it is very difficult to measure the concentration of oil in the water column over large areas and at frequent enough time periods It is also difficult to determine how much oil is left on the water surface as there are no methods available for measuring the thickness of an oil slick and the oil at the subsurface often moves differently than the oil on the surface The quantitative method is not used in modern monitoring practices Instead, a relative measure of dispersant effectiveness is made Quantitative measures are difficult because effectiveness values depend on establishing a mass balance between oil in the water column and that left on the surface Insitu fluorometry can be used to give an indication of the relative concentration of the oil in the water column Some protocols to this have been developed, e.g., SMART (Special Monitoring of Advanced Response Technologies) protocol 16.2.5 Equipment Availability A large amount of dispersant and application equipment is required to mount an operation for a large spill This must be preplanned, as described in Section FIGURE 16.7 View of a dispersant test showing the yellow-to-coffee-colored plume from effective dispersiondnote the remaining oil Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 597 16.1.4 Depending on the jurisdiction, equipment and dispersant can be obtained by prior agreement from various organizations including the Marine Spill Response Corporation (MSRC), Clean Harbors Environmental Services, Inc., Clean Caribbean and Americas (formerly Clean Caribbean Cooperative), Clean Bay Incorporated, National Response Corporation, Marine Pollution Control, and FOSS Environmental & Infrastructure in the United States Some of these organizations are able to assist for a fee or can lease equipment and operators Another important factor to consider is the time required to deliver additional dispersant and equipment to the site, especially considering the short time windows For most scenarios, the time window is less than 48 hours as calculated using Appendix B Significant amounts of dispersant and dispersant application equipment must therefore be prepositioned close to potential spill sites 16.2.6 Equipment Checklist The process that should be followed for preplanning has been laid out in Section 16.1.4 An equipment checklist should be developed for the specific operation to be carried out in the plan This will vary from scenario to scenario, with different types of oil and local conditions It must be ensured that a process such as that outlined in Figures 16.1 and 16.2 can be implemented once a spill occurs 16.2.7 Conducting the Operation In the early stages of spill management, questions may arise as to whether or not a dispersant application will be effective A simple test as described here can answer that question The suggested procedure is to obtain a sample of the actual spilled oil and a sample of the water in the area As soon as practical after the samples are obtained, about L of the water sample is placed into a bottle with a narrower neck (to exaggerate the oil measurement) and filled to the start of the neck Using an etching tool or special marker, a line is placed at the top of the water level to indicate where the oil would start About mL (or drops) of the dispersant to be used is added to 10 mL of oil This is mixed briefly and then poured into the test vessel A mark is placed at the top of the oil The test vessel is shaken vigorously for minute and let stand for 10 minutes and the top of the new oil level is marked About half the oil should be dispersed before proceeding with full-scale dispersant application For information purposes, the oil and dispersant laboratory effectiveness result should be obtained and compared to this value If this test is positive or the oil is known to be dispersible, the dispersant operation will proceed When applying dispersant, the best tactic is to apply the chemical to the thickest portions of the oil This is generally done visually, although infrared cameras can greatly assist by identifying the heavy portions of the oil Personnel in the spotter aircraft will give the required directions The operation 598 PART | VI Treating Agents is continued for as long as the oil is thick and effectiveness is being noted as described in Section 16.2.4 The operation should be stopped if any of the following conditions are noted: lack of effectiveness, change in spill trajectory, a longer time than the precalculated time window, deteriorating weather conditions for flying, lack of wave energy, or any interferences to safe operations 16.3 SAFETY AND POSTDISPERSION ACTIONS 16.3.1 Worker Health and Safety Precautions Worker safety should be a prime consideration during the dispersant operation All personnel involved in a dispersant operation should complete a 40-hour hazmat course or the equivalent course in the relevant country Personnel involved in a dispersant operation should be familiar with the technology and procedures in this guide It is recommended that experienced operations staff attend at least a oneday course on the use of spray equipment and that an additional day be spent practicing spray operations and any emergency procedures Personnel who are not totally familiar with equipment deployment and operations should spend at least one week in training and practice All members of the helibucket operating team require extensive training This training should be provided only by a highly experienced lead person, such as the helibucket supervisor Operators and ground support personnel should generally participate in at least three days of training, including several practice runs The size, structure, and navigational equipment of any vessels used must be suited to the wind, sea state, carrying requirements, and visibility conditions expected during the dispersant operation For operations on the open water, vessels should have a reliable positioning system, such as a GPS, compass, or gyrocompass, working radar, working depth sounder, HF radio, VHF radio, and telephone Under the relevant regulations in the country, each vessel is legally required to have the appropriate safety equipment in accordance with the size and type of vessel and the type of operation being undertaken This includes life jackets, survival suits, life boats, life rafts, life-saving rings, flares, firefighting equipment, and navigation lights Any chartered vessel should possess a valid Coast Guard inspection certificate or equivalent certificate for the country in which the operation will be carried out Before chartering a vessel, a survey by a qualified ship surveyor or naval architect is recommended All flying operations must be carried out in accordance with federal flight regulations All aircraft to be used for applying dispersant should be carefully chosen to suit the required tasks Flight plans must take into consideration all relevant weather conditions, such as wind, visibility, cloud types and height, the presence or forecasted presence of fog, precipitation, and sea state Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 599 For helibucket operations, the helicopter must have sufficient lift capacity to carry a pilot, co-pilot, and a helibucket full of dispersant and be equipped with a cargo hook able to sling the helibucket as well as jettison it The pilot must test the jettison mechanism before each operation For safety reasons, twin-engine helicopters are preferred, particularly for offshore operations, as they are more powerful than single-engine machines and can gain altitude faster If a singleengine helicopter is used, it must be equipped with floats to facilitate emergency landings The helicopter must comply with the relevant regulations regarding helicopter maintenance and the operation being undertaken When arranging for helicopter services, it is recommended that the performance capability of the aircraft and its suitability for its intended use be confirmed with the helicopter pilot and/or helicopter operator Only the pilot and co-pilot, or one other person if required for the spray activation, should ride in the helicopter during the helibucket operation, and all should wear a survival suit During nearshore operations, updraft and downdraft winds against cliffs must be considered In case of mechanical difficulty, emergency landing locations for the helicopter should be identified in advance through site surveillance The public should not be exposed to sprayed dispersant exceeding the recommended human health concern levels The most concern would be the exposure to overspray or drip from the nozzles during overflight People who may be affected by the dispersant operation, even if only remotely, must be briefed about the operation An important part of the safety program for a dispersant operation is establishing minimal safety zones The safety zones established for the environmental issues should be sufficient for human populations as operations should not take place nearshore Safety zones on the sea around the dispersant operation should be on the order of 0.5 km to avoid interfering with vessel traffic and to prevent spray from landing on surface vessels or workers in the area 16.3.2 Follow-Up Monitoring It has been proposed that dispersant application be monitored to determine whether or not the initial spray had any effect The protocols currently consist of some visual criteria and often a surface monitoring program consisting of using in-situ fluorometers to gauge the relative effectiveness of a dispersant application The current published methods including the SMART (Special Monitoring of Advanced Response Technologies) and the SERVS (Shoreline Environmental Research Facility) protocols not assure that effectiveness is gauged accurately There is still potential for answers that are completely opposite to the actual situation Furthermore, the current protocols are limited by basic physical and chemical problems so that at best they are estimates of whether the dispersant application is completely ineffective or somewhat effective 600 PART | VI Treating Agents Monitoring oil concentrations in the water column would provide useful scientific information, although this information may not be useful to the incident commanders because of the complexities of the measurements Visual surveillance is at this time the primary means of determining the effectiveness of the dispersant application At least one experienced person should be employed for the visual surveillance to be effective It is also recommended that buoys be used to track the plume and the remaining slick Davis Drifters can be used to track the plume, and slick tracker buoys can be used to track the remaining slick Further visual surveillance of the slicks is necessary for at least one day The visual surveillance should be documented with photographs Good quality digital still pictures are the best The color quality must be good in order to distinguish between white (dispersant only) and yellow (dispersed oil) plumes All images require timecoding And finally, in conducting the visual surveillance, it must be recognized that there are a large number of false positives and negatives These are summarized here 16.3.2.1 Visual Indications That Show More Effectiveness Than Actually Occurred The following visual indications could create the impression that dispersion has occurred when in fact there is little or no dispersion HerdingdThis is the phenomenon whereby the oil is pushed aside by the dispersant, resulting in a clear path behind the application vehicle A dispersant application in which the oil was herded without any apparent effectiveness is shown in Figure 16.8 Dispersant-only plumedOnce in the water, dispersant forms a whitish plume until it mixes to a greater extent with the water Such plumes could FIGURE 16.8 View of a dispersant application where herding has occurred This photo does not show any visible effectiveness Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 601 FIGURE 16.9 View of a dispersant application where dispersant-only plumes are seen Part of this is caused by dispersant ineffectiveness on the heavy oil coming from the ship be mistaken for dispersed oil as opposed to dispersant only Figure 16.9 shows a situation in which the dispersant has largely run off heavy oil A closeup of this is shown in Figure 16.6 Herding into smaller, unseen stripdOil is often herded into small strips that are not visible from the air SpreadingdDispersants increase the tendency of the oil to spread The surface slick may spread out to thicknesses that are not visible Lacingd“Lace” is a sheen of oil with “holes” in it that are caused by smaller drops of dispersant leading to herding The “lace” is usually visible only from the surface and not from the air 16.3.2.2 Visual Indications That Show Less Effectiveness Than Actually Occurred The following visual indications could create the impression that little or no dispersion is occurring when in fact there is some or significant dispersion Plume under remaining slickdThe dispersed oil plume may move under the remaining slick Plume not developed at time of observationdThe dispersed oil plume can take 15 to 60 minutes to develop to a maximum Poor visibility conditionsdThe dispersed plume is not highly visible and can be obscured by haze and fog It is unlikely, however, that a test application would be conducted under such conditions ADDITIONAL INFORMATION ASTM Guide for Oil Spill Dispersant Application Equipment; Boom and Nozzle Systems, F-141307 West Conshohocken, PA: American Society for Testing and Materials; 2007 602 PART | VI Treating Agents ASTM Standard Test Method for Determination of Deposition of Aerially-Applied Oil Spill Dispersants, F-1738e07 West Conshohocken, PA: American Society for Testing and Materials; 2007 ASTM, Guide for Ecological Considerations for the Use of Oilspill Dispersants in Freshwater and Other Inland Environments, Lakes, and Large Water Bodies, STP F 1210e08 Philadelphia, PA: American Society for Testing and Materials; 2008 ASTM, Guide for Ecological Considerations for the Use of Oilspill Dispersants in Freshwater and Other Inland Environments, Rivers, and Creeks, STP F 1231e08 Philadelphia, PA: American Society for Testing and Materials; 2008 ASTM, Guide for Ecological Considerations for the Use of Oilspill Dispersants in Freshwater and Other Inland Environments, Ponds, and Sloughs, STP F 1209e2008 Philadelphia, PA: American Society for Testing and Materials; 2008 ASTM, 2465, Standard Guide for Oil Spill Dispersant Application Equipment: Single-Point Spray Systems West Conshohocken, PA: American Society for Testing and Materials; 2007 Cedre, Merlin F In: Using Dispersants to Treat Oil Slicks at Sea, www.cedre.fr; December 2009 Committee on Understanding Oil Spill Dispersants Efficacy and Effects (National Research Council of the National Academies)(NAS), Oil Spill Dispersants: Efficacy and Effects Washington, DC: National Academies Press; 2006 Exxon Mobil Dispersant Guidelines Reston, Virginia: Exxon Mobil Corporation; 2008 Fingas MF A Review of Literature Related to Oil Spill Dispersants, 1997‑2008 Anchorage, Alaska: Prince William Sound Regional Citizens’ Advisory Council (PWSRCAC) Report; 2008 Fingas MF Oil Spill Dispersants: A Technical Summary, Chapter 15; 2010 IPIECA Net Environmental Benefit Analysis London, UK: International Petroleum Institute for Environmental Consultation; 1993 IPIECA Chemical Dispersion London, UK: International Petroleum Institute for Environmental Consultation; 1993 Lewis A, Merlin F, Daling P, Reed M, Applicability of Oil Spill Dispersants: Part I, Overview European Maritime Safety Agency, EMSA, London, 2009 603 Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills APPENDIX A SPECIFIC SPILL SCENARIOS AND DISPERSION STRATEGIES Scenario Dispersion at Sea Location: At sea Position: Offshore Proximity of Oil to Resources: A large slick of oil well away from the shore but heading to shore Condition of Oil: The oil is light or medium crude slick and is more than mm thick, fresh, and not emulsified Weather and Sea State: Seas of 0.5 to m Protection Target: Birds and mammals nearshore, shoreline Scenario Dispersion at Sea Location: At sea Position: Offshore Proximity of Oil to Resources: A large slick of oil well away from the shore but heading to sea (with a probability of it heading to shore in the future) Condition of Oil: The oil is light or medium crude slick and is more than mm thick, fresh, and not emulsified Strategy General This is the absolutely ideal condition for dispersion Verify wind and current direction to ensure that dispersing the slick will not affect people, property, or environmentally sensitive areas As a first response, as much of the slick as possible can be dispersed Ensure that sufficient resources are available as soon as possible to deal with at least the leading edge of the slick If the pre-test or data show that the oil is marginally dispersible, continue operation but stop if effectiveness is not seen Dispersant Strategy Focus attention on the thick leading portion of the slick The slick should be approached from downwind Monitoring Aircraft overflights should be carried out to ensure that the slick is being dispersed and that the plume is not heading toward sensitive areas A standby boat could be used to take water samples or conduct fluorometry The dispersant operation should be stopped if it is seen that it is not effective Strategy General This is an ideal condition for dispersion, however protecting shoreline amenities is less of a priority Verify wind and current direction to ensure that dispersing the slick will not affect people, property, or environmentally sensitive areas As a first response, as much of the slick as possible can be dispersed Ensure that sufficient resources are available as soon as possible to deal with at least the leading edge of the slick If the pre-test or data show that the oil is marginally dispersible, continue operation but stop if effectiveness is not seen Dispersant Strategy Focus attention on the thick leading portion of the slick (Continued ) 604 PART | VI Scenario Dispersion at Sea Weather and Sea State: Seas of 0.5 to m Protection Target: Birds and mammals nearshore, shoreline if the oil changes its offshore trajectory Scenario Dispersion at Sea Location: At sea Position: Offshore Proximity of Oil to Resources: A large slick of oil well away from the shore but heading to shore Condition of Oil: The oil is light or medium crude slick and is more than mm thick, fresh, and not emulsified Weather and Sea State: Seas greater than m but currently less than m, winds >20 m/s or 40 knots Protection Target: Birds and mammals nearshore, shoreline Treating Agents Strategy The slick should be approached from downwind Monitoring Aircraft overflights should be carried out to ensure that the slick is being dispersed and that the plume is not heading toward sensitive areas A standby boat could be used to take water samples or conduct fluorometry The dispersant operation should be stopped if it is seen that it is not effective Strategy General This is a marginal condition for dispersion Verify that the operation can be done safely before proceeding Verify wind and current direction to ensure that dispersing the slick will not affect people, property, or environmentally sensitive areas As a first response, as much of the slick as possible can be dispersed Ensure that sufficient resources are available as soon as possible to deal with at least the leading edge of the slick If the pre-test or data show that the oil is marginally dispersible, continue operation but stop if effectiveness is not seen Dispersant Strategy Focus attention on the thick leading portion of the slick The slick should be approached from downwind Monitoring Aircraft overflights should be carried out to ensure that the slick is being dispersed and that the plume is not heading toward sensitive areas The dispersant operation should be stopped if it is seen that it is not effective Scenario Dispersion in a Bay Strategy Location: Bay Proximity of Oil to Resources: A large slick of oil well away from the shore but heading to sea Condition of Oil: The oil is light or medium crude slick and is more than mm thick, fresh, and not emulsified General This is a marginal condition for dispersion Verify wind and current direction to ensure that dispersing the slick will not affect people, property, or environmentally sensitive areas Verify that the depth for at least km is above 10 m or the local restriction As a first response, as much of the slick as possible can be dispersed 605 Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills Scenario Dispersion in a Bay Weather and Sea State: Seas of 0.5 to m Protection Target: Birds and mammals nearshore, shoreline if the oil changes its offshore trajectory Water Depth: More than 10 m (or local restriction) for at least km Strategy Ensure that sufficient resources are available as soon as possible to deal with at least the leading edge of the slick If the pre-test or data show that the oil is marginally dispersible, continue operation but stop if effectiveness is not seen Dispersant Strategy Focus attention on the thick leading portion of the slick The slick should be approached from downwind Monitoring Aircraft overflights should be carried out to ensure that the slick is being dispersed and that the plume is not heading toward sensitive areas A standby boat could be used to take water samples or conduct fluorometry The dispersant operation should be stopped if it is seen that it is not effective APPENDIX B NOMOGRAMS TO CALCULATE SPREADING AND VISCOSITY WITH TIME TABLE B1 Calculation of Spreading and Viscosity Change Spill Size Area (sq km) at Time Type tons hour 12 hours 24 hours 48 hours light crude 100 1000 49 85 149 10000 312 1205 2041 3508 100 1000 49 84 146 10000 302 1200 2040 3492 100 1000 49 84 146 10000 249 1144 2067 3773 medium crude heavy crude (Continued ) 606 PART | VI Treating Agents TABLE B1 Calculation of Spreading and Viscosity Changedcont’d Slick Thickness (mm) Type tons hour 12 hours 24 hours 48 hours light crude 100 2.2 0.7 0.5 1000 6.7 2.4 1.7 10000 12 5.1 3.6 2.4 100 2.2 0.8 0.5 1000 6.7 2.4 1.7 10000 12 5.1 3.7 100 2.3 0.8 0.6 1000 2.6 1.9 1.2 10000 12 5.5 2.7 medium crude heavy crude Viscosity mPa.s Type tons hour 12 hours 24 hours 48 hours light crude 100 46 196 347 1220 1000 28 125 226 810 10000 22 88 155 550 100 310 1300 2300 6700 1000 198 830 1500 4500 10000 163 590 1070 31,100 100 1460 2900 4600 30,000 1000 1390 2300 3500 220,000 10000 1380 2000 2900 170,000 medium crude heavy crude Rules of thumb e slick thickness should be greater than mm e viscosity should be less than 5000 mPa.s italics shows situations where effective dispersion is unlikely 607 Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills TABLE B2 Spray Coverage and Hours for Different Spill Sizes Hours operation to disperse (within 24 hours time window) 100 1000 Dispersant Coverage Coverage Load (L) per hour (Ha) per day (Ha)) tons tons 10,000 tons small boat 1000 10 80 40 850 20410 small ship 3000 20 160 20 425 10205 supply ship 10,000 30 240 13.3 283 6803 small helicopter 700 170 280 2.4 50 1201 large helicopter 2000 280 800 1.4 30 729 Agricultural spray plane 400 170 270 2.4 50 1201 DC-3 4500 540 2400 0.7 16 378 DC-4 8000 840 4800 0.5 10 243 DC-6 11,000 1010 7330 0.4 202 C-130 (Hercules) 13,000 1010 8670 0.4 202 tons of dispersant 50 500 drums of dispersant 25 250 2500 Hours operation to disperse (within 48 hours time window) Dispersant Coverage Coverage Load (L) per hour (Ha) per day (Ha)) 100 1000 tons tons 10,000 tons small boat 1000 10 80 70 1490 35080 small ship 3000 20 160 35 745 17540 supply ship 10,000 30 240 23.3 497 11690 small helicopter 700 170 280 4.1 2060 88 (Continued ) 608 PART | VI Treating Agents TABLE B2 Spray Coverage and Hours for Different Spill Sizesdcont’d Hours operation to disperse (within 48 hours time window) Dispersant Coverage Coverage Load (L) per hour (Ha) per day (Ha)) 100 1000 tons tons 10,000 tons large helicopter 2000 280 800 2.5 53 1250 Agricultural spray plane 400 170 270 4.1 88 2060 DC-3 4500 540 2400 1.3 28 650 DC-4 8000 840 4800 0.8 18 420 DC-6 11,000 1010 7330 0.7 15 350 C-130 (Hercules) 13,000 1010 8670 0.7 15 350 tons of dispersant 50 500 drums of dispersant 25 250 2500 * Presuming the maximum number of hours of operation and daylight, per vehicle 10000 10,000 tons Area (sq km) 1000 100 1000 tons 10 100 tons 0.1 100 tons 1000 tons 10,000 tons 10 20 30 40 Time (Hours) FIGURE B1 Nomogram for calculating slick area with spill size 50 609 Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills 100 tons 1000 tons 10,000 tons 12 Thickness (mm) 10 10,000 ton 1000 ton Practical thickness limit 10 20 30 40 50 Time (Hours) FIGURE B2 Nomogram for calculating slick thickness with spill size and time 100 ton 1000 ton 10,000 ton Viscosity (mPa.s) 10000 increasing difficulty to disperse 1000 100 10 10 20 30 40 50 Time (Hours) FIGURE B3 Nomogram for estimating oil vicosity time e light crude 610 PART | VI 100 ton 1000 ton 10,000 ton 1e+5 Viscosity (mPa.s) Treating Agents limit of practical dispersion 1e+4 1e+3 increasing difficulty to disperse 1e+2 10 20 30 40 50 Time (Hour) FIGURE B4 Nomogram for estimating oil vicosity with time e medium crude 100 ton 1000 ton 10,000 ton Viscosity (mPa.s) 1e+5 10,000 ton 100 ton limit of practical dispersion 1e+4 increasing difficulty to disperse 1e+3 10 20 30 40 50 Time (Hours) FIGURE B5 Nomogram for estimating oil vicosity with time e heavy crude ... dispersant application to sensitive Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills Oil spill occurs 585 Sensitive areas would benefit Oil is dispersible Chemical chosen as a. .. European Maritime Safety Agency, EMSA, London, 2009 603 Chapter | 16 A Practical Guide to Chemical Dispersion for Oil Spills APPENDIX A SPECIFIC SPILL SCENARIOS AND DISPERSION STRATEGIES Scenario... hours, a thickness that is nearly impossible to treat with dispersants For practical purposes, mm will be taken as the practical limit in this guide Chapter | 16 A Practical Guide to Chemical Dispersion