COMPARISON OF PHYSICAL AND CHEMICAL CHARACTERISTICS OF IN- SITU BURN RESIDUE AND OTHER ENVIRONMENTAL OIL SAMPLES COLLECTED DURING THE DEEPWATER HORIZON SPILL RESPONSE Prepared for: Bureau of Safety and Environmental Enforcement (DOI/BSEE Agreement Code: E13PG00001) Prepared by: Gary Shigenaka, NOAA/ERD

An unprecedented volume of crude oil was burned during the Deepwater Horizon oil spill response, with an estimated 220,000-310,000 bbl of surface oil consumed by in-situ burning over a ten-week period in 2010. Most of the resultant burn residue from these large-scale operations sank in the relatively deep waters of the Gulf of Mexico. However, in late 2010, the deep water royal red shrimp fishery operating north of the Macondo wellhead (also referred to by its lease designation, Mississippi Canyon Block 252, or MC252) and the primary burn zone encountered tarballs at 200 m. At least some of these tarballs were tentatively sourced as Deepwater Horizon in-situ burn residue. This project physically and chemically characterized oil and residue samples from the Deepwater Horizon response as well as laboratory samples of source and burned crude oil to provide insights into the changes that occur when oil is burned. Deepwater Horizon burn operations were confirmed as the source for tarballs recovered in shrimp trawls. Potential markers of burned crude oil were identified in order to distinguish burn residue from other weathered forms of the same crude oil. INTRODUCTION In-situ burning—the controlled combustion of spilled oil in the environment—was one of many remedial techniques employed during the prolonged Deepwater Horizon oil spill response in the Gulf of Mexico in 2010. It has been called the oldest cleanup method applied to oil spills (Fingas, 2011), but documentation of its use and scientific evaluation of its efficacy has been spotty and inconsistent over the years. Fingas (2011) listed 45 on-water in-situ burns performed during spills or experiments between 1958 and 2008. Although the technique was successfully tested during the landmark Exxon Valdez oil spill in Prince William Sound, AK in 1989 (Figure 1), real validation and rigorous scientific evaluation as a response tool occurred in 1993 during a unique experiment off the eastern coast of Canada in 1993. The Newfoundland Offshore Burn Experiment (NOBE, Figure 2) was a collaborative effort among 25 agencies from Canada and the U.S. to conduct two experimental burns of Alberta Sweet crude oil to demonstrate feasibility of burning spilled oil on marine waters, and to collect a wide range of data related to burn parameters and emissions (Fingas et al., 1994a). The NOBE experience was considered to be a logistical and technical success, and yielded a wealth of technical and operational information that has been used as the basis for insitu burn plans and policies ever since. In-situ burning has been used for spill response a number of times over the years on both land and water. Fingas (2011) provided a comprehensive overview of the state of knowledge just prior to the Deepwater Horizon incident and a summary of at-sea applications during oil spill response. In addition to the 45 water-borne examples listed by Fingas, Michel et al. (2005) found it was frequently used on the terrestrial side as well; however, reasonable documentation was available for only 31 of an apparently much larger total. Indisputably, though, the Deepwater Horizon burn operations (Figures 3 & 4) were by far the largest application of the method: an estimated 260,000 barrels (bbl)/10.9 million gallons of oil were burned between April 28 and July 12, 2010 (Federal Interagency Solutions Group, 2010). This volume of oil was equivalent to the total volume estimated to have spilled from the Exxon Valdez, the nation’s largest oil spill prior to the Deepwater Horizon.