Don Aurand

Modelling of dispersant application to oil spills in shallow coastal waters

Abstract 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-zero-volume 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.

Results from Cooperative Ecological Risk Assessments for Oil Spill Response Planning in Galveston Bay, Texas and the San Francisco Bay Area, California

ABSTRACT This paper summarizes the results of two cooperative ecological risk assessments (ERAs) that examined the potential environmental consequences of oil spill scenarios, two in the vicinity of San Francisco Bay, California and one in Galveston Bay, Texas. The goal of the evaluation was to identify the optimum mix of response options for reducing injury to the environment. For these specific scenarios, the participants concluded that only dispersant use, assuming high effectiveness, had the potential to significantly reduce environmental impact when compared to natural recovery. While water-column effects increased with dispersant use, they were not long term and judged to be of less ecological significance than shoreline or water-surface impacts. Aside from dispersant use, only shoreline cleanup was effective in clearly mitigating impacts, and obviously would not prevent the immediate consequences of the spills. The optimum response was viewed as involving some combination of the various response op...

Ecological Risk Assessment Principles Applied to Oil Spill Response Planning

ABSTRACT This paper summarizes the process of a cooperative ecological risk assessment (ERA) that was used to examine the potential environmental consequences of oil spill scenarios in San Francisco Bay, California; Galveston Bay, Texas; and Puget Sound, Washington. The purpose of the ERA process is to evaluate the ecological trade-offs associated with the use of each of five potential oil spill removal options—natural recovery, on-water mechanical recovery, shoreline cleanup, dispersant use, and on-water in situ burning. The desired outcome of the evaluation is identification of the optimum mix of response options in reducing injury to each specific environment. Evaluations at each location were accomplished through a series of facilitated workshops involving technical experts and resource managers from as many stakeholder organizations as possible. At these workshops, the participants developed relative ecological risk evaluations for response options. At the conclusion of each ERA, the workshop partici...

Lessons Learned in Ecological Risk Assessment Planning Efforts

ABSTRACT There is growing interest in the United States for using the full mix of environmentally appropriate countermeasures during spill response to achieve the highest level of environmental protection and recovery possible. Determining the right mix of technologies, including mechanical recovery, shoreline cleanup, dispersants, and monitoring (no active response), is particularly challenging in sensitive and valuable estuaries through which high volumes of bulk oil shipment transit. This paper summarizes an ecological risk assessment (ERA) project to consider the potential effectiveness and effects of using dispersants, in addition to conventional countermeasures, to mitigate the impacts of oil spilled into the marine and nearshore environments and to facilitate preparedness efforts at the federal, state, local, and industry level. Sponsored by industry and federal and state agencies, the primary goal was to bring technical and resource experts together to use their collective knowledge and experience...

Ten Years of Research by the U.S. Oil Industry to Evaluate the Ecological Issues of Dispersant Use: An Overview of the Past Decade

ABSTRACT The Marine Spill Response Corporation (MSRC) and the American Petroleum Institute (API) recently completed a multiyear research program on dispersants and dispersed oil consisting of four elements: information synthesis and dissemination, improved laboratory methods for toxicity evaluation, mesocosm testing, and field experiments. These research efforts contributed to the recent changes in the way dispersants are viewed in the United States. When combined with other research findings from the last 10 years, this information, now available to response planners, greatly improved and contributed to a growing interest in the use of dispersants, including the potential for the extension of preauthorization areas. The primary objectives of this paper are to summarize the objectives of the program, highlight major findings, and identify the sources where the results can be examined in detail.

GOALS, OBJECTIVES, AND THE SPONSORS' PERSPECTIVE ON THE ACCOMPLISHMENTS OF THE CHEMICAL RESPONSE TO OIL SPILLS: ECOLOGICAL EFFECTS RESEARCH FORUM (CROSERF)

ABSTRACT In the summer of 1994, a group of organizations sponsoring research related to the environmental effects of chemical oil spill treating agents organized a working group to coordinate their research activities in this area. The purpose of Chemical Response to Oil Spills: Ecological Effects Research Forum (CROSERF), as defined at the first meeting, was to provide a mechanism for the exchange of ideas and coordination of research to state, federal, and international agencies; industry; academic researchers; and consultants engaged in research on the ecological effects of oil spill response chemicals, especially dispersants. Each of the primary sponsors had its own objectives for the program, and contributed to the design of the cooperative research efforts. Over the past 7 years, there have been nine CROSERF meetings, each serving to direct the research efforts and resolve issues of importance to all of the participants. Most of the program objectives were achieved, but declining research funds limi...

THE USE OF CONSENSUS ECOLOGICAL RISK ASSESSMENTS TO EVALUATE OIL SPILL RESPONSE OPTIONS: LESSONS LEARNED FROM WORKSHOPS IN NINE DIFFERENT LOCATIONS

ABSTRACT Since 1998, the United States Coast Guard (USCG) and various partners in industry and government have applied a standardized consensus ecological risk assessment process in workshops aroun...

Design and Implementation of a Mesocosm Experiment On The Environmental Consequences of Nearshore Dispersant Use

ABSTRACT In April 1998 the first full-scale oil spill experiment was run at the Coastal Oilspill Simulation System (COSS) Facility in Corpus Christi, Texas. The facility contains nine 110-foot long...

Learnings from the Texas Nearshore Dispersant Demonstration Project

ABSTRACT This project defines circumstances where a dispersant demonstration might be considered for an estuarine oil spill in Texas. In seeking approval for a spill of opportunity demonstration project, we developed criteria defining a viable dispersant response for consideration by the Region VI Regional Response Team. This paper presents the criteria and their rationale developed for Galveston Bay and Corpus Christi Bay, along with the results of recent training exercises. The criteria define the size and general location of an oil spill that might be considered appropriate for a trial dispersant application, and implementation of response and monitoring within a 2-hour window from notification. They are based on descriptions and characterizations of the habitats and species at risk in coastal areas, concentration and duration of dispersed oil plumes that might be generated in a response, potential impacts of these exposures, and the environmental trade-off between implementing mechanical response and ...

Using Laboratory, Mesocosm, and Field Data In Ecological Risk Assessments for Nearshore Dispersant Use

ABSTRACT In the United States, pre-approval for dispersant use exists only in conservatively defined circumstances of water depth and/or distance off shore. Historical records suggest that most opp...