Search

Introduction. General Mechanism of Action of Chemical Dispersants. Chemical Formulation of Dispersant Agents. Factors Affecting Chemical Dispersion of Oil and Its Measurement. Properties and Chemistry of Oil. Dispersant Composition. Dispersant Application. Mixing Energy. Dispersant-To-Oil Ratio (DOR). Oil-To-Water Ratio (OWR). Temperature. Salinity. Sampling and Analysis Method. Laboratory Testing of Dispersant Performance. Laboratory Testing Methods. Advantages and Disadvantages of Different Laboratory Tests. Rapid Field Tests for Estimating Dispersant Performance. Field Tests of Dispersant Applications. Summary and Recommendations-Laboratory Studies. References. Index. Appendix A: Preparation Approach for this Book.

NO. 2017-167 As part of the Natural Resource Damage Assessment (NRDA) effort following the Deepwater Horizon (MC252) blowout and oil spill in 2010, over 5,300 water samples were forensically evaluated both as evidence of exposure and to validate oil fate and transport modelling. In addition to whole water-sample grabs, particulate-oil and dissolved-phase samples from the subsurface release were separated (filtered) in the field to provide detailed information on the partitioning behavior of oil droplets in a deepwater plume (1,000–1,400m) extending to the southwest (SW) of the wellhead. Offshore, the subsurface plume was visually observed and photographed using remotely operated vehicles (ROVs), and tracked in conductivity, temperature, and depth (CTD), dissolved oxygen (DO), and fluorometry profiles. The farthest reach of the plume was 412 km (250 mi) SW of the wellhead as confirmed by multiple lines of evidence (i.e., depth, fluorometry spikes, DO sags, and dispersant indicators) and out to 267 km as weathered, phase-discriminated, confirmed hydrocarbon profiles. With increasing time and distance from the wellhead, the plume’s polycyclic aromatic hydrocarbon (PAH) signal became diluted and eventually no longer detectible using selected-ion-monitoring (SIM) gas chromatography/mass spectrometry (GC/MS), although the plume was still discernible in the corroborating data. We hypothesize that microbial degradation at depth converted the PAH and aliphatics into oxygenated and polar products not detectible using SIM GC/MS methods. Near-surface oil samples showed evidence of substantial dissolution weathering as the oil droplets rose through the water column, and further evaporative losses of lower-molecular-weight n-alkanes and aromatic hydrocarbons occurred after the oil reached the surface. Surface oil also showed evidence of photo-oxidation of alkylated chrysenes and triaromatic steranes. Typical of surface oil dynamics, increases in dissolved and particulate-oil fractions were observed in the shallow sub-surface as a result of both dispersant effects and wave reentrainment of surface films. Dispersant treatment effects, both as surface applications and injected at the wellhead, showed uniquely enhanced-dissolution weathering patterns in PAH profiles with limited or delayed microbial degradation of saturated hydrocarbons (SHC) close to the wellhead. From an oil-fate-and-transport standpoint, these data document that the dispersant applications at depth were functionally effective in breaking up the oil droplets and thereby preventing some portion of the oil from reaching the surface.

As analytic instruments and methods have improved over the decades, so too, have insights into the fate and behavior of oil–water mixtures. Particularly relevant are understanding and documenting oil phase signatures that, while yielding forensic insights in our early studies, have led to the recent development of phase-specific methods appropriate for the forensic study of oiled water. The forensic applications of these methods include source matching, weathering, deconfounding background contaminants, distinguishing dissolved and particulate phases within whole water samples, and documenting chemical dispersant effects on polycyclic aromatic hydrocarbons (PAH) profiles. These methods, when collectively applied to deep-sea water of the Gulf of Mexico following the Deepwater Horizon (DWH) blowout, were used to ultimately track the subsurface plume of DWH-impacted water 412 km across the Gulf of Mexico to a final sample confirmed with only a trace dissolved-PAH pattern and supporting information.

During the Deepwater Horizon blowout, unprecedented volumes of dispersant were applied both on the surface and at depth. Application at depth was intended to disperse the oil into smaller microdroplets that would increase biodegradation and also reduce the volumes buoyantly rising to the surface, thereby reducing surface exposures, recovery efforts, and potential stranding. In forensically examining 5300 offshore water samples for the Natural Resource Damage Assessment (NRDA) effort, profiles of deep-plume oil droplets (from filtered water samples) were compared with those also containing dispersant indicators to reveal a previously hypothesized but undocumented, accelerated dissolution of the polycyclic aromatic hydrocarbons (PAH) in the plume samples. We interpret these data in a fate-and-transport context and conclude that dispersant applications were functionally effective at depth.

Forensic chemistry assessments documented the presence of Macondo (MC252) oil from the Deepwater Horizon (DWH) spill in offshore water samples collected under Natural Resource Damage Assessment (NRDA) protocols. In ocean depths, oiled water was sampled, observed, photographed, and tracked in dissolved oxygen (DO) and fluorometry profiles. Chemical analyses, sensor records, and observations confirmed the shifting, rising oil plume above the wellhead while smaller, less buoyant droplets were entrapped in a layer at ~1000–1400 m and advected up to 412 km southwest. Near-surface oil samples showed substantial dissolution weathering from oil droplets rising through the water column, as well as enhanced evaporative losses of lighter n-alkanes and aromatic hydrocarbons. Dispersant effects from surface applications and injected at the wellhead were seen in oil profiles as enhanced weathering patterns (increased dissolution), thus implying dispersants were a functionally effective mediation treatment. Forensic assessment methods are detailed in the Supplemental information (SI).

An oil droplet size model was developed for a variety of turbulent conditions based on non-dimensional analysis of disruptive and restorative forces, which is applicable to oil droplet formation under both surface breaking-wave and subsurface-blowout conditions, with or without dispersant application. This new model was calibrated and successfully validated with droplet size data obtained from controlled laboratory studies of dispersant-treated and non-treated oil in subsea dispersant tank tests and field surveys, including the Deep Spill experimental release and the Deepwater Horizon blowout oil spill. This model is an advancement over prior models, as it explicitly addresses the effects of the dispersed phase viscosity, resulting from dispersant application and constrains the maximum stable droplet size based on Rayleigh-Taylor instability that is invoked for a release from a large aperture.

After a spill, oil is present in water as both dissolved and particulate (oil-droplet) phases due to entrainment and dissolution/weathering processes. The two phases, capable of physically separating and remixing in a body of water, complicate forensic evaluations but also contribute information on waterborne fate and transport. Identifying and tracking each phase in field samples has high forensic value in developing interpretive scenarios of weathering and exposure processes and for providing data germane to modeling and toxicology studies in damage assessments. Samples can be parsed into phase components either physically in the field using portable filtration equipment or later with data evaluation methods developed to parse out unfiltered samples using a weathered particulate-oil reference series generated from a few field-filtered samples. If done properly, sampling the water column for oil hydrocarbons during or after an oil spill can be highly insightful but the task is challenging and technically demanding with multiple opportunities to get it wrong, especially without feedback until weeks or months later when the data come back from the lab. This chapter presents water-sampling issues (and solutions), methods of forensically assessing quantified data, and adaptive sampling strategies that prove effective in tracking a deep submerged plume.

Oil-spill fate and transport modeling may be used to evaluate water column hydrocarbon concentrations, potential exposure to organisms, and impacts of oil spills with and without dispersant use. Important inputs to transport modeling for such analyses are current velocities and turbulent dispersion coefficients. Fluorescein dye studies off San Diego, California, were used to calibrate an oil transport model by hindcasting movement and dispersion of dye. The oil spill model was then used to predict subsurface hydrocarbon concentrations and potential water column impacts if oil were to be dispersed into the water column under similar conditions. Field-collected data included surface currents calculated from high-frequency radar data (HF-Radar), near-surface currents from drifter measurements drogued at several depths (1m, 2m, 4m or 5m), dye concentrations measured by fluorescence, spreading and dye intensity measurements based on aerial photography, and water density profiles from CTD casts. As the dye plume quickly extended throughout an upper mixed layer (7–15m), the horizontal dye movements were better indicated by the drifters drogued to a depth near the middle of that layer than the HF-Radar, which measured surface (∼top 50 cm) currents (including wind drift). Diffusion rates were estimated based on dye spreading measured by aerial photography and fluorescence-depth profiles. The model used these data as inputs, modeling of wind-forced surface water turbulence and drift as a function of wind speed and direction (based on published results of fluid dynamics studies), and Stokes law for droplet rise/sinking rates, to predict oil transport and dispersion rates within the water column. Use of such diffusion rate data in an oil fate model can provide estimates of likely dispersed oil concentrations under similar conditions, which may be used to evaluate potential impacts on water column biota. However, other conditions with different patterns of current shear (due to background currents, tidal currents, and wind stress) should be examined before these results can be generalized.

The California Department of Fish and Game Office of Spill Prevention and Response (CA OSPR) is utilizing oil-spill fate and transport modeling to develop the time and spatial scales, and equipment needs, for a formal Dispersed Oil Monitoring Plan (DOMP). When fully implemented, the DOMP will aid in documenting hydrocarbon concentrations in the water column, potentially exposed organisms (zooplankton), and the impacts of entrained oil and dissolved hydrocarbons with and without dispersant applications. Fluorescein dye studies off San Diego, California (USA) have been completed to test the operational framework for repeated sampling of dispersed oil plumes as outlined in the DOMP, to allow evaluation of high-frequency radar (HP-Radar) for providing surface current input data to oil spill models, and to provide verification of model-predicted movement of subsurface oil (dye) by comparison with drogue movement and measured dye concentrations over three dimensions and time. Aerial photodocumentation, subsurface drogues, dye transport, and HF-Radar were used to measure near-surface current fields at varying depths. High-resolution subsurface dye-plume structure was mapped using an in situ GPS-coupled towed fluorometer equipped with pressure sensors to provide dye concentration data as a function of time, position, and depth. In addition, data from the more traditional Special Monitoring of Applied Response Technology (SMART) protocols utilized by the U.S. Coast Guard (USCG) were compared with the in situ towed-fluorometer measurements, and conventional CTD data were collected to determine the mixed layer depth, an important variable in monitoring dispersion of oil in the water column. As a result of these efforts, significant progress has been made on developing and testing sampling protocols for the DOMP, and nearly continuous and synoptic data have been obtained from seven cruises conducted over a 12-month period. These data sets (available on-line through the Coastal Response Research Center (CRRC) website: http://www.crrc.unh.edu/) are being analyzed and integrated to support oil spill model development and verification with direct applicability to spill response decision making, net environmental benefit analysis, natural resource damage assessments, and educating the spill community and public.

Oil stranded by the 1989 Exxon Valdez spill has persisted in subsurface sediments of exposed shores for 16 years. With annualized loss rates declining from approximately 68% yr(-1) prior to 1992 to approximately 4% yr(-1) after 2001, weathering processes are retarded in both sediments and residual emulsified oil ("oil mousse"), and retention of toxic polycyclic aromatic hydrocarbons is prolonged. The n-alkanes, typically very readily oxidized by microbes, instead remain abundant in many stranded emulsified oil samplesfrom the Gulf of Alaska. They are less abundant in Prince William Sound samples, where stranded oil was less viscous. Our results indicate that, at some locations, remaining subsurface oil may persist for decades with little change.

Chemical analysis of large populations of floating (n=62) and stranded (n=1174) Macondo oils collected from the northern Gulf of Mexico sea surface and shorelines during or within seven weeks of the end of the Deepwater Horizon oil spill demonstrates the range, rates, and processes affecting surface oil weathering. Oil collected immediately upon reaching the sea surface had already lost most mass below n-C8 from dissolution of soluble aliphatics, monoaromatics, and naphthalenes during the oil's ascent with further reductions extending up to n-C13 due to the onset of evaporation. With additional time, weathering of the floating and stranded oils advanced with total PAH (TPAH50) depletions averaging 69±23% for floating oils and 94±3% for stranded oils caused by the combined effects of evaporation, dissolution, and photo-oxidation, the latter of which also reduced triaromatic steroid biomarkers. Biodegradation was not evident among the coalesced floating oils studied, but had commenced in some stranded oils.

Sampling zooplankton is a useful strategy for observing trace hydrocarbon concentrations in water because samples represent an integrated average over a considerable effective sampling volume and are more representative of the sampled environment than discretely collected water samples. We demonstrate this method in Port Valdez, Alaska, an approximately 100 km 2 basin that receives about 0.5–2.4 kg of polynuclear aromatic hydrocarbons (PAH) per day. Total PAH (TPAH) concentrations (0.61–1.31 μg/g dry weight), composition, and spatial distributions in a lipid-rich copepod, Neocalanus were consistent with the discharge as the source of contamination. Although Neocalanus acquire PAH from water or suspended particulate matter, total PAH concentrations in these compartments were at or below method detection limits, demonstrating plankton can amplify trace concentrations to detectable levels useful for study.

The natural oil seeps off Coal Oil Point (Santa Barbara), California, release an estimated 100–150 bbl of oil per day to the marine environment. This project proposed to conduct a series of dispersant trials using these seeps to intercalibrate NOAA's Scientific Monitoring of Advanced Response Technologies (SMART) UV/Fluorescence-based protocols with finite measurements of dissolved aromatics and dispersed oil droplets in the water column and to evaluate a unique oil-boomldispersant-application technology (NeatSweep). Following an elaborate and lengthy permitting process including cooperation from multiple regulatory agencies and organizations, laboratory tests indicated that although fresh produced oil from nearby Platform Holly could be treated (>70% effectiveness), dispersing the weathered 11° API gravity seep oil was totally ineffective (0%). Limited field tests then verified the laboratory findings that the seep oil could not even be dispersed with Corexit 9500, a commonly used dispersant for heavily weathered and viscous oils. Lacking reasonable alternatives (including the use of intentional spills), the project was halted before full-scale field implementation. This paper documents the development of the research plan, the steps required to obtain the necessary permits, and the results from the limited laboratory and field tests that were completed. The planning and permitting efforts for this project are provided so that others with similar needs or goals might benefit. A brief discussion is provided on the limitations of using natural seep oils for spill response research and on the difficulties with spill-of-opportunity research during actual spill events. The importance of controlled experimental discharges of oil is discussed along with the pros and cons of such deliberate spills.

For years, it has been known that oil released in seawater partitions into dissolved and oil-droplet phases; however, there has been little effort to discriminate between the phases in oil spill Natural Resource Damage Assessment (NRDA) programs. In 1999, portable field equipment was built for this task. By filtering 3.5 L volumes of seawater at the time of collection, method detection limits are improved and it is possible to discriminate between the phases, thereby improving understanding of oil fate and transport processes and providing more accurate toxicological assessments. First utilized in response to the M/V New Carissa oil spill at Coos Bay, Oregon, this approach proved highly successful in discriminating the phase signatures. The resulting data demonstrated that while the dissolved-phase signal appeared in places such as crab tissue and interstitial water on an otherwise clean beach, the oil-droplet phase appeared in tissues of filter-feeding Coos Bay mussels and oysters. In Port Valdez, Alaska, the portable sampler was used to assess the phase signatures in effluent from the Ballast Water Treatment Facility (BWTF) at the Alyeska Marine Terminal. The signatures were then used to reveal differential seasonal uptake in mussels at several sites within the port. During the winter, when the water column is unstratified, both dissolved- and oil-droplet phase contaminants from the BWTF diffuser can reach the upper water column, where they are transported as a surface microlayer by winds and surface currents throughout much the fjord. In the late spring, summer, and fall, when the water column is highly stratified, only the dissolved-phase components are observed in the mussels along the shoreline, as the oil droplets are preferentially trapped below the thermocline. These findings have compelled a reassessment of monitoring methods for oil spill NRDA efforts, National Pollutant Discharge Elimination System (NPDES) permitting, and general environmental monitoring.

A field-portable water-sampling system was designed and fabricated for collecting adequate volumes of seawater to meet the quantitation requirements to support Natural Resource Damage Assessment (NRDA) toxicity determinations and modeling efforts following an oil spill. This system is a significant improvement to conventional water sampling equipment and includes the ability to filter water samples at the time of collection, thereby providing critical differentiation between truly dissolved constituents and dispersed oil droplets. The system can be quickly and easily deployed from shoreline structures (piers and breakwaters) and/or vessels of opportunity to provide essential data during the early stages of a spill. Likewise, data collected with the system can be used to document dispersant effectiveness and provide information relating to seafood exposure, tainting, and toxicity issues. In many oil-spill NRDA efforts, water-column effects from dissolved components and dispersed oil droplets have not been adequately quantified or documented because: (1) samples are not obtained early enough after the spill event; (2) insufficient volumes are collected; and (3) the wrong constituents are analyzed. Generally, EPA hazardous-materials sampling approaches are followed, leading to inadequate sample sizes (e.g., 40 mL for volatile component analyses and 1-L samples for dissolved/dispersed constituents). Analytically, EPA semivolatile gas chromatography/mass spectrometry (GC/MS) SW-846 Method 8270 is often specified for polynuclear aromatic hydrocarbons (PAH). These sample sizes are not large enough to meet the detection limits required for most marine hydrocarbon analyses (de Lappe et al., 1980; Payne, 1997 and references therein), and the EPA PAH target analyte list does not include the majority of alkyl-substituted one-, two-, and three-ring aromatics that are the primary dissolved constituents actually present in the water column following an oil spill (Sauer and Boehm, 1991). As a result, water column effects are often written off as being short-lived or insignificant. Alternatively, impacts are often assessed by computer modeling efforts with limited field validation. In either event, there is inadequate profiling of the extent and duration of petroleum hydrocarbon exposure to marine organisms. Furthermore, when adequate volumes of water have been collected and the proper target analytes have been specified, provisions have not been taken to differentiate between truly dissolved components and dispersed oil droplets. Consequently, later data analyses are unreliable in their ability to reflect conditions as they actually existed during the early stages of the spill. For example, PAH analyses of unfiltered water samples are confounded by the facts that: (1) a significant, but unknown fraction of discrete oil droplets in the water column will rise to the surface with time; (2) high levels of dispersed oil droplets will raise detection limits of dissolved PAH; and (3) it is impossible to determine how much of the PAH is in the truly dissolved state where it will persist as a toxic fraction to exposed organisms and how much is simply associated with slightly less toxic oil droplets that are subject to relatively rapid removal by resurfacing. The equipment and field implementation approach described in this paper can provide samples that are not subject to the aforementioned problems.

Just after midnight on March 24, 1989, the 987-foot tank vessel Exxon Valdez grounded on Bligh Reef in Prince William Sound (PWS), Alaska, releasing approximately 10.8 million gallons of North Slope crude oil into the Sound. The energetic environmental conditions in PWS and the extensive cleanup activities led to wide dispersion of the Exxon Valdez oil, which simultaneously underwent biodegradation and photooxidation. Although some more refractory residuals of the petroleum (e.g., high molecular weight PAH, resins, and asphaltenes) persist, many of these constituents are not readily distinguishable from other petroleum sources and naturally occurring hydrocarbon residues. We estimate that approximately 20% of the spilled oil evaporated and underwent photolysis in the atmosphere; approximately 50% biodegraded either in-situ on beaches or in the water column; approximately 14% was recovered or disposed; < 1% remained in the water column (except as biodegradation products); approximately 2% remained on intertidal shorelines; and approximately 13% remained in subtidal sediments, mostly in the GOA and again mostly as highly weathered residuals. 60 refs., 3 figs., 2 tabs.

Outdoor flow-through seawater wave tank studies and model predictions on the chemical and physical fate of Prudhoe Bay crude oil in subarctic waters are compared with field observations from the Exxon Valdez oil spill in Prince William Sound, Alaska. Excellent agreement is obtained between predicted and observed parameters, including evaporative loss of lighter distillate cuts, water content in mousse, density, viscosity, oil/water and oil/air interfacial surface tension, and chemical composition. As predicted from wave tank studies, water column samples of dispersed and dissolved oil and suspended particulate material collected from several heavily oiled sheltered coves and bays in Prince William Sound indicate that little oil reached the near-shore benthic environment during the first few weeks after the spill.

Oil-weathering processes in ice-free subarctic and Arctic waters include spreading, evaporation, dissolution, dispersion of whole-oil droplets into the water column, photochemical oxidation, water-in-oil emulsification, microbial degradation, adsorption onto suspended particulate material, ingestion by organisms, sinking, and sedimentation. While many of these processes also are important factors in ice-covered waters, the various forms of sea ice (depending on the active state of ice growth, extent of coverage and/or decay) impart drastic, if not controlling, changes to the rates and relative importance of different oil-weathering mechanisms. Flow-through seawater wave-tank experiments in a cold room at ?35°C and studies in the Chukchi Sea in late winter provide data on oil fate and effects for a variety of potential oil spill scenarios in the Arctic. Time-series chemical weathering data are presented for Prudhoe Bay crude oil released under and encapsulated in growing first-year columnar ice through spring breakup.

During the emergency phase of an oil or hazardous material spill, natural resource managers and trustees must quickly develop and implement study plans to collect ephemeral data on the extent and degree of contamination and the potential biological injury resulting from the spill. Manuals and guidelines have been developed by various groups, yet these documents have proven to be too difficult to use during the chaotic, early days of a spill emergency. To provide better guidance, a series of brief (two-page) protocol summaries have been prepared for the types of sampling activities likely to be conducted during the emergency phase of spill, supporting both response and natural resource damage assessment (NRDA) objectives. Protocols have been prepared for collection of samples of the source oil(s), water samples, intertidal sediments, subtidal sediments, and shellfish tissues for chemical and histopathological analysis. Protocols are also being prepared for procedures to measure salt marsh injury, visual estimates of abundance and percent cover in quadrats, and quantitative measurements of infaunal abundance.

In the aftermath of the 1989 Exxon Valdez oil spill, a Long Term Environmental Monitoring Program (LTEMP) has been regularly sampling mussels (and some sediments) for polycyclic aromatic and saturated hydrocarbons (PAH and SHC) at sites in Port Valdez, Prince William Sound, and the nearby Gulf of Alaska region. After 1999, a decreasing trend appears in total PAH (TPAH) in tissues at all sites with current values below 100 ng/g dry weight (many below 50 ng/g). Currently, most samples reflect a predominantly dissolved-phase signal. This new low in TPAH likely represents ambient background levels. Synchrony in TPAH time-series and similarities in the hydrocarbon signatures portray regional-scale dynamics. The five inner Prince William Sound sites show similar composition and fluctuations that are different from the three Gulf of Alaska sites. The two Port Valdez sites represent a unique third region primarily influenced by the treated ballast water discharge from the Alyeska Marine Terminal. Prince William Sound has reverted to a stable environment of extremely low level contamination in which local perturbations are easily detected.

A Marine Oil Pollution Index (MOPI) is presented to characterize the hydrocarbon burdens of marine tissues or sediments. The index incorporates the ratios of unresolved to resolved components, even n -alkanes to odd n -alkanes, and branched hydrocarbons to n -alkanes, plus the total recoverable aliphatic and aromatic hydrocarbon concentrations from gas chromatographic analysis, to yield a single value that can be used to compare the relative magnitude of oil contamination in a series of tissue or sediment samples. Several examples of tissue samples from the intertidal mussel Mytilus californianus are presented, along with results from the 1975-78 BLM Southern California Baseline Study and MMS-sponsored Georges Bank Monitoring Program, to demonstrate the usefulness of generating single index values for time-series or spatial trend analyses. MOPI values calculated for analyzed tissue samples reflect varying degrees of exposure, ranging from pristine to heavily petrogenic conditions. A MOPI value calculated for a drilling fluid sample containing diesel oil residues also reflects the heavily petrogenic contamination.

Hydrocarbons in sediments and hydrocarbons and trace metals in tissues from Georges Bank were analyzed to evaluate potential changes to the henthic environment resulting from exploratory drilling operations. Sediment hydrocarbon concentrations varied with grain size: concentrations up to 2·5μg/g dry weight total aromatic equivalents occurred in the fine-grained sediments of Lydonia Canyon and the ‘Mud Patch’ area south of Martha's Vineyard, whereas concentrations were less than I μg/g dry weight in sediments from the shallow areas of Georges Bank, at a regional control site, and at the site of drilling operations. Increases in total aromatic equivalents from approximately 0·1 μg/g dry weight to 0·4 μg/g dry weight were measured in sediments from a site 0.25 km from the drill rig concurrent with drilling operations. Petrogenic hydrocarbons were detected in both drilling fluid extracts and in sediments collected during drilling operations, suggesting short-term deposition of drilling discharges in near-rig sediments. Drilling discharge residues were not observed in the near-rig sediments one month after drilling operations were terminated. Furthermore, hydrocarbon residues from drilling discharges werenot observed in sediments from stations located at distances greater than 6 km from the drill site either during or subsequent to the drilling operations.