Forensic Chemical Analyses Coupled with Detailed Site and Water Column Observations Used to Locate the Primary Cause of a Persistent Sheen off Louisiana’s Coast

Oral Presentation

Prepared by E. Overton1, C. Reddy2, R. Camilli3, W. Bryant4
1 - Louisiana State University, Rm 1265 Energy Coast and Environemnt Bldg,, Depart of Environmental Sciences, LSU, Baton Rouge, Louisiana, 70803, United States
2 - Makepeace Environmental Solutions, LLC, 12 Buzzards Bay Avenue, Woods Hole, MS, 02543, United States
3 - Navistar Corp., , Woods Hole, MS, 02543, United States
4 - C K Associates Environmental Consultants, 7170 Perkins Road, Baton Rouge, LA, 70810, United States


Contact Information: ebovert@lsu.edu; (225)578-8634


ABSTRACT

A sheen forms near the mouth of the Mississippi River caused by a production platform destroyed in 2004 by Hurricane Ivan. Aerial observations of the sheen’s surface locations over many years show the initial formation point varies over an area of ~ 2 square miles in the vicinity of the downed platform. Previous sampling showed two bottom sediment areas with significant concentrations of oil resides, but 2012/13 sheen analyses did not provide consistent forensic matches to these residues. To identify the bottom location that is primarily contributor to the sheen formation, ~57 discrete GPS-referenced surface sheen samples were collected just as the oil surfaced, thus minimizing weathering of the samples, in March and April 2017. These samples were analyzed by GCFID and GCMS to identify and quantitate the concentration of the normal and isoprenoid alkanes and unresolved complex mixtures, PAH compositions, isomer and homolog compositional profiles for the C4 naphthalenes and DBT, and the hopane (191 ion) and sterane (217 and 218 ions) compositions. Analytical data were correlated with aerial observations, surface Doppler acoustic water column profiles for detection of rising oil droplets and gas bubbles, and top to bottom water column current measurements. These analytical data were examined by a four-tiered interpretative approach that looked for similarities and differences between: various 2017 sheen samples; 2017 sheen samples with previously collected sheen samples; 2017 sheen samples and various oil residues in bottom sediment samples from hotspot locations near the former well-bay and downed jacket areas; and 2017 sheens and oil from various production wells in Block 21 GOM. The Tiers 1 and 2 forensic evaluation process revealed that surface sheens continue to be heterogeneous, and yet have common compositional features that were also found in oily bottom residues collected near the fallen jacket.