Slick thickness measurements at Ohmsett by dip plate and sorbent pad. On April 20, 2010, an explosion occurred on the Deepwater Horizon (DWH) oil rig in the Gulf of Mexico, approximately 50 miles southeast of the Mississippi Delta. The resulting oil spill was of national significance, exposing and injuring natural resources in many areas of the northern Gulf of Mexico. The magnitude and duration of the DWH oil spill was unprecedented.

As a result, natural resource trustees – specifically, state and federal agencies – initiated a natural resource damage assessment (NRDA). As part of this assessment, the National Oceanic and Atmospheric Administration (NOAA), U.S. Fish and Wildlife Service (USFWS), and the state of Louisiana contracted with Abt Associates to assist with the assessment of natural resource exposure to contaminants such as oil and dispersant, injuries resulting from that exposure, and compensation to make the public whole.

Since the summer of 2010, Abt staff designed, directed, and managed laboratory and field-based chemical investigations. These include:

Detailed chemical and physical characterizations of oil/water mixtures – such as water accommodated fractions – using several different oil samples and mixing methods with and without chemical dispersants;

• Detailed chemical and physical characterizations of sediment samples contaminated with oil in the field and spiked with oil in the laboratory;
• Surface oil sheen thickness measurements and chemical characterizations;
• Oil weathering rates in the laboratory under simulated natural conditions;
• Field and wave tank investigations of oil concentrations in the water column and surface oil sheen thickness estimates and detection using remote sensing techniques; and
• Analysis and interpretation of oil concentration and composition data from water and sediment samples collected in the field to determine exposure.

Much of these chemistry data have been used in conjunction with toxicity testing data to aid in determining and quantifying injuries to marine and estuarine biota exposed to oil. We also played a key role in authoring many sections of the DWH Programmatic Damage Assessment and Restoration Plan (PDARP) in close collaboration with NOAA and the U.S. Fish and Wildlife Service. This included section 4.2 on Natural Resource Exposure, section 4.3 on Toxicity, Chapter 4 in the PDARP, as well as several technical reports and peer-reviewed manuscripts.
 
Read more about this work:

• Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic Environmental Impact Statement
• Technical Reports cited in the PDARP for Chemistry (Section 5.11.2) and chemistry related to aquatic toxicity (Section 5.12.2) are available through the Administrative Record for the Deepwater Horizon Response and Restoration