Modelling the Effects of Chemical Dispersant on the Fate of Spilled Oil: Case Study of a Hypothetical Spill near Saint John, NB (original) (raw)
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The proposed Energy East pipeline project has raised concerns about potential oil spills in Saint John, New Brunswick, due to increased tanker traffic. While environmental conditions such as strong tide and current could pose challenges for using mechanical recovery methods if a spill occurs in the area, chemical dispersant could be an alternative oil spill countermeasure. However, the application of chemical dispersant in shallow water and costal zones remains an issue of debate. To study if chemical dispersant could be effective for potential oil spills in Saint John, a 3-dimensional model was used to simulate the transport of oil following a hypothetical release of 1000 m 3 Arabian Light crude under winter conditions. A stochastic approach was used to take into account the uncertainties of environmental inputs. The results show a significant reduction of oil ashore, and enhanced biodegradation with dispersant application, but these effects were accompanied by an increase of oil in sediment and water column, which is a concern. While the results are only conclusive for the selected scenarios of winter release, the method could be extended to other months and seasons of the year to support more detailed net environmental benefit analysis regarding dispersant application.
Modelling of dispersant application to oil spills in shallow coastal waters
Environmental Modelling & Software, 2004
Application of dispersants in shallow water remains an issue of debate within the spill response community. An experimental oil spill to evaluate potential environmental impacts and benefits of applying dispersants to spills in shallow water has therefore been under consideration. One site being considered was Matagorda Bay, on the Texas coast. Coupled three-dimensional oil spill and hydrodynamic models were used to assist in the design of such an experiment. The purpose of the modeling work was to map hydrocarbon concentration contours in the water column and on the seafloor as a function of time following dispersant application. These results could assist in determining the potential environmental impact of the experiment, as well as guiding the water column sampling activities during the experiment itself. Eight potential experimental oil spill scenarios, each of 10 bbl in volume, were evaluated: 4 release points, each under two alternate wind conditions. All scenarios included application of chemical dispersants to the slick shortly after release. Slick lifetimes were under 5 h. Due to the shallow depths, some fraction (2-7%) of the released hydrocarbons became associated with bottom sediments. The algorithms used for the oil droplet-sediment interactions are theoretical, and have not been verified or tested against experimental data, so the mass balances computed here must be considered tentative. Currents computed by the hydrodynamic model are consistent with previous observations: the circulation is largely tidally driven, especially near the ship channel entrance. In the center of the bay, the circulation appears relatively weak. The use of water column drifters with surface markers during the experiment would augment model results in assisting activities to monitor concentrations. These simulations suggest that the eventual behavior of an oil droplet cloud in the middle of the bay will be relatively insensitive to release point or time in the tidal cycle. A limited analysis was run to evaluate model sensitivity to the oil-sediment sorption coefficient. Increasing this coefficient by a factor of 10 results in an approximately linear increase in the fraction of oil in the sediments. Sensitivity of estimated time-to-zerovolume for the 0.1-ppm concentration contour demonstrated that the model prediction of 3.5 days was associated with an uncertainty of ±12 h for a release of 10 barrels. This time estimate is also a function of the oil-sediment interaction rate, since more oil in the sediments means less oil in the water column.
Estimating the Usefulness of Chemical Dispersant to Treat Surface Spills of Oil Sands Products
Journal of Marine Science and Engineering
This study examines the use of chemical dispersant to treat an oil spill after the initial release. The natural and chemically enhanced dispersion of four oil products (dilbit, dilynbit, synbit and conventional crude) were investigated in a wave tank. Experiments were conducted in spring and summer to capture the impact of temperature, and the conditions in the tank were of breaking waves with a wave height of 0.4 m. The results showed that natural dispersion effectiveness (DE) was less than 10%. But the application of dispersant increased the DE by an order of magnitude with a statistically significant level (p < 0.05). Season (spring versus summer) had an effect on chemical DE of all oils, except for the conventional oil. Thus, the DE of dilbit products is highly dependent on the season/temperature. A model was fitted to the DE as a function of oil viscosity for the chemically dispersed oil, and the correlation was found to be very good. The model was then combined with a previ...
International Oil Spill Conference Proceedings, 1981
Dispersant use is a factor that may partly determine the fate and effects of spilled oil. A series of quantitative field experiments has been initiated to simulate conditions following nearshore treatment of a floating oil slick or following the cleaning of a spill stranded on the shore. The basic experimental design is a series of treatments (Forties or Nigerian crude oil, BP 1100WD dispersant, or oil plus dispersant) applied to sets of experimental plots in a range of intertidal and subtidal communities. Biological recording includes frequency and density measurements of plants and animals, and hydrocarbon analysis is by capillary gas liquid chromatography and computerised gas chrornatography–mass spectrometry. Additionally, the effects of dispersant on the movement and fate of oil in different types of sediment is being investigated using a laboratory sediment column and controllable temperature seawater system. The columns have been successfully used in the modeling of low-energ...
Oil Spill Treatment Strategy Modeling for Georges Bank
Proceedings, 1979
As part of a larger project assessing the environmental impact of treated versus untreated oil spills, a fates model has been developed which tracks both the surface and subsurface oil. The approach used to spread, drift, and evaporate the surface slick is similar to that in most other oil spill models. The subsurface technique, however, makes use of a modified particle-in-cell method which diffuses and advects individual oil/dispersant droplets representative of a large number of similar droplets. This scheme predicts the timedependent oil concentration distribution in the water column, which can then be employed as input to a fisheries population model. In addition to determining the fate of the untreated spill, the model also allows for chemical treatment and/or mechanical cleanup of the spilled oil. With this capability, the effectiveness of different oil spill control and removal strategies can be quantified. The model has been applied to simulate a 34,840 metric ton spill of a No. 2-type oil on Georges Bank. The concentration of oil in the water column and the surface slick trajectory are predicted as a function of time for chemically treated and untreated spills occurring in April and December. In each case, the impact on the cod fishery was determined and is described in detail in a paper by Reed and Spaulding presented at this conference.
Dispersion of spilled oil in freshwater systems: Field trial of a chemical dispersant
Oil and Chemical Pollution
The impacts of oil and dispersed oil on freshwater ecosystems were examined in afield experiment conducted as part of the Freshwater Oil Spill Research Program. In July 1985, 3 m 3 of Normal Wells crude oil were spilled on each of two fen lakes. The slick on one lake was treated with the dispersant Corexit 9550. Core_x# 9550 was effective in removing the oil from the water sulface even though wave energy was very low. The oil or dispersed oil had little detectable short or long term impact on all water quality parameters measured, or on the microbial populations and activities in the water column and sediments of both lakes. Untreated oil caused more damage than the dispersed oil to floating aquatic plants and the shoreline vegetation, but new growth within the affected areas was observed one month after treatment. Seasonal regrowth of vegetation in all areas affected by the treatments appeared normal. Our results suggest that the best response to oil contamination in isolated fen lakes is no action at all. However, floating oil or oil washed ashore could pose a significant threat to indigenous wildlife or its habitats. Under these conditions, chemical dispersion may prove to be an
Ecological Impact Analysis of Dispersants and Dispersed Oil: An Overview
Journal of Environmental Informatics Letters, 2021
Soaring oil demand, as a result of industrial development, boosts oil exploration and production activities at sea, even into deeper and icier waters. The transportation of the oils, as well as the potential spill accidents and associated pollutions are thus increased. There is an urgent call for contingency planning with effective and eco-friendly oil spill cleanup responses. Dispersant applications can facilitate the breaking up of oil slicks into small oil droplets, allowing their rapid dispersion, dissolution, dilution and biodegradation in the water column. Dispersants have been recognized as effective oil treating agents and well adopted. Nearly 7 million liters of chemical dispersants, mostly Corexit ® 9500A, were used after the Deepwater Horizon oil spill incident. However, debates over dispersants continued with major concerns about their environmental impacts and the ecological toxicity, which need to be well reviewed and tackled. Therefore, this study summarized the recent lab-and meso-scale studies and field trials on the ecological impact analysis of dispersants and the chemically dispersed oils. By providing an up-to-date review of the ecological toxicity and environmental impact assessment, this study would help to bridge the knowledge gaps in the field and facilitate future dispersant applications.