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Dispersing, burning & skimming DWH oil
During the annual meeting of Pacific States/British Columbia Oil Spill Task Force in Anchorage on Aug. 24, some members of the investigation team that developed the U.S. Coast Guard’s Incident Specific Preparedness Review, or ISPR, for the Deepwater Horizon oil spill response commented on lessons learned from the use of various techniques during the response.
Dispersant use
ISPR team member John Tarpley, chief of the Regional Operations Branch for NOAA’s Office of Response and Restoration, Emergency Response Division, in Seattle, Wash., spoke to the task force about the use of dispersants, a technique that became a core part of the response. Dispersants, acting somewhat like dish soap, break oil into microscopic particles that swill around below the water surface, to eventually be consumed by oil-eating bacteria.
The oil industry was well prepared for dispersant use and largely ran the Deepwater Horizon dispersant operation, Tarpley said.
Dispersant application started two days after the oil spill began, with dispersants sprayed into oil slicks from boats and aircraft, and with dispersant also injected at the seafloor into the oil spewing from the Macondo well. The response eventually used a total of 1.8 million gallons of Corexit dispersant, Tarpley said.
The dispersants proved quite effective, ultimately mopping up an estimated 16 percent of the oil that flowed from the well, he said. And although the long-term impacts of such massive dispersant use are still under investigation, EPA laboratory testing indicates that the Corexit dispersant has low toxicity, leading to moderate dispersed oil toxicity after application, Tarpley said.
Although there is pre-authorization for the use of dispersants in the Gulf of Mexico, dispersant plans did not consider the possibility of having to apply dispersant continuously to an out-of-control oil well, Tarpley said. And there is no national policy for dispersant use and pre-approval. NOAA is reviewing its program for monitoring the effectiveness of dispersant use, with the feasibility of operating this monitoring program in a remote region such as the Chukchi Sea being one issue requiring investigation, he said.
Burning effective ISPR team member Larry Dietrick, director of the Division of Spill Prevention and Response in the Alaska Department of Environmental Conservation, talked to the task force about the in situ burning of oil, another key technique used in the Deepwater Horizon response. In situ burning would likely prove an important tool in dealing with any Alaska offshore oil spill, Dietrick said.
In situ burning disposed of an estimated 5 percent of the oil spilled from the Macondo well, with 91 percent of the burn operations proving successful.
“This is a good tool … and I think this event showed the scale on which it can be used,” Dietrick said.
Experience from the Gulf of Mexico is leading to the development of improved designs for the fire boom used to herd oil for a burn and continuing investigations into the use of chemical agents for oil herding; and more work is needed to improve the techniques used to recover burn residues, Dietrick said.
Skimming capacity One of the findings from investigations of the Deepwater Horizon response is that there was a difference between the documented capacity of oil skimmers available to remove oil from the water surface and the total amount of oil that skimmers deployed in the Gulf of Mexico actually retrieved. Skimmers are estimated to have removed about 3 percent of the oil spilled from the Deepwater Horizon accident.
The capacity ratings of skimmers are important because they become part of the evaluation of whether an oil spill contingency plan adequately accommodates the worst possible oil discharge that could occur as the result of a spill.
ISPR team member Brian House, CEO of Moran Environmental Recovery and director of the Spill Control Association of America, told the task force that the skimming capacity delivered to the Deepwater Horizon response met a 500,000-barrel oil recovery planning standard for the response. However, the skimming capacity greatly exceeded the quantity of oil that the skimmers actually recovered.
In fact, there was a massive nationwide call for skimmers, but many of those skimmers were left sitting, unused. House attributed this underutilization to the fact that it is necessary to select appropriate skimming technology for a particular oil recovery situation, with the rate at which a particular skimming device is able to encounter oil significantly impacting its skimming ability.
In addition, the interaction of skimming with other recovery techniques can reduce skimming efficiency, with skimming being less effective on oil left after the use of in-situ burning, for example, than when used to recover untouched oil slicks, House said.
A fresh look It is now necessary to take a fresh look at assessing skimmer oil recovery rates, considering the complete gamut of potential operating environments, weather conditions and other operational variables, he said.
“It’s an emotional issue I suppose, but it’s a big one,” House said. “Like everything else it’s (about) driving awareness, performance and planning.”
—Alan Bailey
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