Federal Interagency Group Issues Peer-Reviewed 'Oil Budget' Technical Documentation

Oil Spill Calculations Released in August Undergo Further Review

November 23, 2010

The Federal Interagency Solutions Group, established at the request of the U.S. Coast Guard and authorized under a directive from the National Incident Commander (NIC), is releasing today a peer-reviewed report that details the scientific calculations of the Deepwater Horizon BP Oil Spill “Oil Budget Calculator” response tool announced last August. The report, developed in collaboration with federal and independent scientists and following an extensive review of the initial findings, revises as necessary the estimated short-term fate of the oil discharged from the wellhead through mid-July when the well was capped.  

The Oil Budget Calculator’s purpose was to describe the short-term fate of the oil and to guide immediate efforts to respond to the emergency. It does not provide information about the impact of the oil, nor indicate where the oil is now. The Oil Budget Calculator uses collected or reported data, such as the amount captured at the wellhead, combined with model-projected estimates based on historical oil spill data for similar types of oil, as well as the expertise and observations of oil- and oil spill-response scientists from government agencies, academia and the energy industry.

Improvements have been made to the calculator since it was first used. The revised Oil Budget Calculator was adjusted based on modified calculations and modeling, as well as additional knowledge about the Deepwater Horizon spill provided by the science team. The revised calculations provide the basis for the updated budget issued in the report, as well as the best- and worst-case scenarios.

“As we said in August, we promised to provide the technical documentation for the Oil Budget report and refine our estimates where possible. This report fulfills that promise. The Oil Budget was not created to draw conclusions about the long-term environmental impact. The estimates were designed to guide operational response decisions and provide clarity on how much oil could be captured or mitigated and how much oil was not recoverable,” said Jane Lubchenco, Ph.D., under secretary of commerce for oceans and atmosphere and NOAA administrator. “Fully understanding the damages and impacts of the spill on the Gulf of Mexico ecosystem is something that will take time and continued monitoring and research by federal and academic scientists.”

Today’s report provides the technical basis underlying the Calculator’s oil fate estimates used to help respond to the spill. This report, following additional assessment and peer-review, is largely consistent with early results released by the federal government. The most significant change is a doubling of the expected amount of oil classified as “chemically dispersed” — revised from 8% to an estimated 16% with a possible range of between 10% and 29%. Additional data and studies have over the course of the past few months led the oil budget team to relax certain initial conservative assumptions with regard to the effectiveness of dispersant operations. The early estimate of the percentage of "other" (or, "residual") oil was 26%; the current version of the Calculator estimates it as 23%, and qualifies this estimate with the belief that, with high confidence, the true percentage should be between 11% and 30%.

Oil Budget (Released Aug. 4)

Oil Budget Technical Report

Category % of Total Category % of Total Change
Direct Recovery 17% Direct Recovery 17% None
Burned 5% Burned 5% None
Skimmed 3% Skimmed 3% None
Chemically Dispersed 8% Chemically Dispersed 16% +8%
Naturally Dispersed 16% Naturally Dispersed 13% -3%
Evaporated or  Dissolved 25% Evaporated or Dissolved 23% -2%
Other 26% Other 23% -3%

The three lead editors of the report were William Lehr, Ph.D., senior scientist with NOAA’s Office of Response and Restoration; Sky Bristol, science coordinator for informatics, U.S. Geological Survey; and Antonio Possolo, Ph.D., chief of the Statistical Engineering Division, National Institute of Standards and Technology. The report includes major contributions from 15 international academic institutions, government agencies and industry experts as well as additional contributions from a wide-ranging group of others. The peer-review process was independently coordinated through the University of New Hampshire’s Coastal Response Research Center in Durham, N.H.

The report specifically recommends future research and planning to be directed to three areas that would reduce the uncertainty of the estimates and improve future response activities:

(1) Protocols for surface and subsurface sampling: Although oil samples were collected for impact assessment, samples were not systematically collected to support the development of the Oil Budget Calculator. For example, samples often came from skimming barges where oil and water mixtures in different states of degradation were blended together. Future response plans should specify methods for gathering proper representative samples.

(2) Dispersed oil droplet size: A major improvement in estimating dispersant efficiency would be possible if practical operational tools and methods existed to characterize droplet size distribution of subsurface oil.

(3) Basic models for longer-term processes: Although longer-term processes such as biodegradation often happen outside the time frames of the response, understanding and being able to predict such longer-term changes may be useful in making response decisions.

This report was written to document for the scientific community and other interested parties the technical underpinnings of the Calculator and provide recommendations for future research and refinement of the tool for possible use in future spills. The full 217-page report, including appendices and peer-review team comments, is available online.

Download the report from RestoretheGulf.gov

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