Three Years of Shoreline Cleanup Assessment Technique (SCAT) for the Deepwater Horizon Oil Spill, Gulf of Mexico, USA

Abstract

The oil from the 2010 Deepwater Horizon spill in the Gulf of Mexico was documented as stranding on 1,773 kilometers (km; 1,102 miles) of shoreline as of May 2013. Of the shorelines oiled, beaches comprised 50.8%, marshes 44.9%, and other shoreline types 4.3%. One year after the spill began, oil remained on 830 km; two years later, oil remained on 685 km and three years later, oil remained on 632 km, with 74% of the shoreline classified as trace (<1%) oiling degree. Shoreline cleanup activities were authorized on 660 km, or 73.3% of oiled beaches. Because the oil stranded over a three-month period and at a period in time when the beaches were in a relatively eroded condition, the oil became deeply buried and posed many challenges to its removal. The continued remobilization of oil buried in both intertidal and nearshore habitats resulted in the chronic re-oiling of sand beaches at trace levels for over three years, thus the slow rate of decline in the shoreline oiled lengths. Treatment of sand beaches in the first year focused on use of mechanical beach cleaners and excavation and sifting of deeply buried oil to minimize clean sediment removal. Later treatments were mostly manual except for mechanical excavation of deeply buried oil in Louisiana beaches in 2012 and 2013. Passive, manual, and mechanical treatments were authorized on 71 km, or 8.9% of oiled marshes and associated habitats, though actual treatment was conducted in smaller zones within these segments. Intensive marsh cleanup treatments were limited to ~1-2% of oiled marshes Gulf-wide and focused on areas with thick persistent marsh oiling. The Shoreline Cleanup Assessment Technique (SCAT) Program was the most complex and long lasting of any past spill. The SCAT Program evolved as needed to support the changing requirements and many challenges over the duration of the response. Many of the tools and products developed and used will be of value for future spill responses.