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

The Deepwater Horizon oil spill began on 20 April 2010 and was finally capped on 15 July 2010, resulting in the release of 4.09 million barrels into the Gulf of Mexico, excluding an estimated 810,000 barrels that were directly recovered from the wellhead, thus not released to the Gulf (McNutt et al. 2011). A Shoreline Cleanup Assessment Technique (SCAT) Program was established on 28 April 2010 as part of the Environmental Unit under the Planning Section and will end when all segments are moved out of the emergency response sometime in 2014. The shoreline response program went through four stages of response (Michel et al. 2013), with a detailed plan for each stage that described the process for conducting shoreline inspections, issuing shoreline treatment recommendations (STRs), inspecting against habitat-specific cleanup endpoints, moving to the next stage of the response, and eventually to determining that removal actions were deemed complete.

During the Deepwater Horizon spill response, up to 18 SCAT teams, consisting of Federal, State, local, and BP representatives, conducted field surveys to document the location, degree, and character of shoreline oiling using standard methods and terminology (NOAA, 2013; Owens and Sergy, 2000). The shoreline response program encompassed four stages, defined primarily to recognize changes in oiling threat, oiling conditions, progression through cleanup operations, and seasonal factors as summarized below:

Stages I/II Nearshore and Shoreline Response Plan: The first two stages of the response (May to September 2010) covered the period during which oil continued to strand onshore. Stage I activities involved on-water recovery of floating oil slicks in nearshore waters. Stage II activities involved the initial cleaning of bulk oil from intertidal areas until the source was controlled. To minimize the impact of clean-up operations, comprehensive shoreline cleanup activities were deferred until free-floating oil on the surface waters was reduced to a minimal level and the risk of shoreline oiling was diminished. As such, SCAT shoreline surveys during this stage were rapid and focused on locating floating oil adjacent to the shoreline and stranded bulk oil for immediate removal, especially where such oil could remobilize and spread to other areas.

Stage III Shoreline Treatment Implementation Framework: Once source control was assured and the bulk of free-floating oil had been recovered or was stranded on shore, response activities entered the third stage of shoreline cleanup operations. During this period (September 2010 to March 2011), detailed SCAT surveys were conducted of all shorelines within the Area of Response. Site- and habitat-specific STRs generated within the SCAT Program and approved by the Unified Command were issued for each shoreline segment or group of segments where treatment was authorized, specifying the area and types of treatment operations to be conducted. Technical working groups were formed to reach consensus on appropriate cleanup methods and “2010 No Further Treatment (NFT) guidelines” for each habitat type. It was realized that additional shoreline treatment would be required over time; however, the goal was to complete the majority of active cleanup operations by Spring 2011, when shoreline use by nesting birds, sea turtles, and people increased. Treatment of amenity beaches included intensive sifting, excavation, and manual removal methods. An intensive treatment strategy was developed and refined for marsh areas with thick persistent oiling. Response actions involved raking and cutting to remove oiled vegetation mats, oiled wrack, and residual surface oiling using manual and mechanical teams (Zengel and Michel 2013).

Stage IV Shoreline Response Plan: This stage (March to November 2011) started with a resurvey of all affected shorelines to document Spring 2011 conditions and determine the need for further cleanup to meet “2011 NFT guidelines,” which were similar to those in Stage III. New Stage IV STRs were issued for shorelines requiring treatment. When shoreline segments met the 2011 NFT guidelines, they were moved from active response into a Patrol and Maintenance status because of the risk of : exposure of buried oil by wind erosion; re-oiling from remobilization of subsurface oil as a result of beach erosion; and remobilization of oil in nearshore submerged mats and on marsh platforms. Stage IV was scheduled for completion by the end of the 2011 hurricane season in the Gulf of Mexico.

Shoreline Cleanup Completion Plan (SCCP): This final stage of the shoreline response (November 2011 and forward) defined the process whereby removal actions would be deemed complete and shoreline segments could be moved out of the response. For the first time in this response, a pathway was defined to determine that shoreline treatment was completed in a particular area. The shoreline-oiling conditions documented by SCAT teams were compared against shoreline cleanup “endpoints.” Once a segment met these final criteria (Tables 1 and 2; which were very similar to the prior NFT guidelines), the segment was removed from active response. The SCCP required surveys of selected shoreline segments after the 2011 Atlantic hurricane season, and multiple post-treatment surveys of segments to assure that oiling conditions continued to meet endpoints. Segments that did not meet endpoints were returned to Operations for further treatment, and the inspection process was repeated.

The SCAT Program managed all of the field data collected by SCAT teams using a Microsoft Access database linked to mapping software (ArcGIS). A large team of SCAT Data Managers conducted data entry and quality assurance, tracked the status of 4,397 shoreline segments, generated a wide range of daily to weekly products to meet the demands of the response, and supported the development of 280 STRs during Stages III and IV (exclusive of many revisions).

Key metrics that are closely watched during an oil spill response include the lengths of shoreline by oiling category over time to gauge the response progress. Of the 7,044 km of shoreline surveyed as of May 2013 (Table 3), 1,773 km (1,102 miles) were oiled at some point during this incident, based on the maximum oiling (the maximum extent and heaviest oiling category recorded for each shoreline segment tracked during the response). Of this, 977.2 km (607 miles) were sand beaches and 795.8 km (494 miles) were marshes and mangroves. The majority of this oiling was in Louisiana with 1,074.5 km of oiled shoreline (60.6% of shoreline oiling in this incident). Florida had 285.6 km (16.1%); Mississippi had 258.5 km (14.6%); and Alabama had 154.5 km (8.7%) of impacted shoreline (Table 4, Figure 1). Based on maximum oiling across all states, 359.8 km (20.3%) of the shoreline oiling were classified as Heavy, 222.3 km (12.5%) as Moderate, 636.8 km (35.9%) as Light, 322.1 km (18.2%) as Very Light, and 232.2 km (13.1%) as Trace. One year after the incident, 46.8% or 830 km of the 1,773 km of impacted shoreline still had some degree of oiling; after two years, 38.6% or 685 km remained oiled; and after three years, 35.6% or 632 km remained oiled. Heavy to moderately oiled shorelines had declined by 87.8% in one year, 95.9% in two years, and 96.2% by three years, compared to maximum oiling conditions (Table 3, Figures 2 and 3).

The shorelines in Florida, Alabama, and Mississippi were moved out of the Deepwater Horizon response in Spring 2013, and segments within Louisiana were moved out of response as “response actions are deemed complete.” New reports of oil on these shorelines are made to the National Response Center, and USCG pollution investigators respond to determine if the oil is from the Deepwater Horizon spill. These investigators recover the oil if feasible. If there is too much oil for them to recover, USCG notifies BP to respond if the oil is determined to be from the Deepwater Horizon spill or a cleanup contractor if it is not.

There were interesting patterns in the types of oil observed by SCAT teams over time. A new SCAT oil type was defined for “surface oil residue balls” (SRBs) and “surface oil residue patties” (SRPs). These oil types were broken up pieces of surface oil residues, semi-cohesive oil and sand mixtures that were 80-90% sand, that originally formed as larger surface oil residue mats or smaller fields of patchy surface oil residue. It was apparent over time that it was not appropriate to call them “tarballs” because SRBs and SRPs were not tar and were mostly composed of sand rather than oil (tar balls are mostly oil). Figure 4 shows the changes in distribution in surface oil types and thickness over time on beaches and marshes. On beaches, there was very little emulsified oil or “mousse” after the first summer and very little surface oil residue after the first year (other than SRBs and SRPs). SRBs became the dominant surface oil type as buried/nearshore mats continued to break up. On marshes, the dominant oil type in the first summer was mousse on the marsh surface and tarry coatings on the vegetation. However, over time, the mousse weathered into tarry coats and thicker (cover) surface oil residues, except where it was buried, trapped under oiled vegetation mats and wrack, or mixed into thick accumulations of fine organic material such as “coffee grounds.” The lack of change in surface residue on the marsh surface over the three-year period indicates that this type of oiling is persistent.

The vast extent of the shoreline that required survey for the Deepwater Horizon oil spill, the eroded nature of the beaches at the time of oiling, the three months of continuous flow of oil, the fragile nature of the Louisiana coastline, tropical storms and hurricanes with associated storm surges, and wildlife and human use of the Gulf Coast, among others factors posed many challenges to the SCAT Program and the successful completion of shoreline treatment. Key challenges included the following:

1. 1)

   Oil that initially stranded onshore for over three months when beaches were in an erosional condition, which resulted in deep burial as well as stranding very high in the supratidal zone (following tropical storms) where it could be buried by wind accretion. Over 100,000 pits, trenches, and augers holes were used to search for and delineate buried oil for removal through the end of 2013. Augers were mounted onto small tracked vehicles that could rapidly excavate sediment borings to 2.5 m depths for inspection.

2. 2)

   Oil that mixed with sediments in the nearshore zone, which resulted in the accumulation of submerged oil mats (SOMs) that were difficult to locate and remove and caused chronic re-oiling as they were buried/exposed and broken up by wave action. These SOMs generated the evolution of what was called “Snorkel SCAT,” where teams worked in waist-deep water and used narrow spades (“sharp shooter” shovels) to excavate sediments to depths of up to 50 cm in a grid pattern to delineate areas for removal by long-arm excavators working from the shoreline. These Snorkel SCAT teams worked closely with Operations to refine areas for removal and confirm that all recoverable oil was removed.

3. 3)

   Restrictions on use of mechanical treatment methods along some sand beaches, which limited the depth of removal actions and resulted in persistence of deeply buried oil for several years. The shoreline erosion and remobilization of oil on sand beaches after Hurricane Isaac crossed Louisiana in August 2012 led to the development of a renewed augering program to identify and removal buried oil from all tidal zones, resulting in the removal of 6.1 million pounds of oiled materials in Louisiana in 2013.

4. 4)

   Cleanup endpoints on amenity beaches that specified “no visible oil” on the surface or in the subsurface sediments These endpoints, and the widely scattered distribution of oil residues in the beach sediments, led to the extensive use of mechanical equipment to excavate and sift sediments to depths of nearly 1.25 m during operations called “Deep Clean” and “Big Dig” in Florida and Alabama. All cleanup endpoints for a habitat also included “or as low as reasonably practicable considering the allowable treatment methods and net environmental benefit,” which was often used when removal amounts reached very low levels on amenity beaches.

5. 5)

   Cessation of both cleanup operations and SCAT surveys during environmental stand-downs in 2011, 2012, and 2013 to avoid disturbance to nesting birds and sea turtles.

6. 6)

   The need for multiple re-surveys of affected shorelines because of trigger points, such as the end of hurricane season or after environmental stand-downs or during the SCCP process.

7. 7)

   Concerns about re-oiling from buried oil or SOMs resulted in a four-step final inspection process under the SCCP that included a pre-inspection to be scheduled at least 48 hours after treatment operations were terminated, a Shoreline Inspection Report-1 (SIR-1) scheduled at least 48 hours after the pre-inspection, a SCAT Monitoring survey within about 25 days later, and a final SIR-2 scheduled within 30 days of the SIR-1. However, weather and sea conditions often delayed completion of these surveys within the specified time periods, particularly in Louisiana where many segments had to be accessed by boat. If a segment failed any of these surveys or inspections and was returned to Operations for further treatment, the process was started over again. Eventually, SCAT teams were allowed, and even required, to “mitigate” oil that did not meet cleanup endpoints when feasible (or within certain limits); and Operations crews were assigned to the SCAT teams to assist in mitigation, again particularly in Louisiana where the amounts of oil removed during mitigation could involve hundreds of pounds of oiled materials. In contrast, in the Eastern states, the amounts of oil mitigated by SCAT teams were in the range of pounds or fractions of pounds during the SCCP inspection process.

One result of the challenges defined above was that reaching the defined cleanup endpoints was, in many places, extremely difficult. The degree of oiling rapidly declined over the first year of the response. Greater than 50% of the oiled shorelines had no oil observed one year after the response, and shorelines classified as having heavy to moderate oiling had declined by nearly 88%. However, over the next two years of the response, the decline in reported length of oiled shoreline slowed significantly with nearly 36% of the surveyed shorelines remaining in an oiled status three years after the spill. Cleanup efforts had not been reduced in the remaining oiled areas; rather the many challenges associated with the cleanup prevented the response from rapidly meeting the cleanup endpoints.

The SCAT program evolved as needed to support the changing requirements and many challenges over the nearly four years of the Deepwater Horizon response. Many of the tools and products developed and used in the response will be of value for future spill responses. However, it is important to recognize that each spill is unique, and SCAT need to remain flexible in scale and complexity according to the shoreline oiling conditions and response needs encountered during each incident.

The BP SCAT Program Managers over time included Richard Santner, Mary Cocklan-Vendl, Bea Stong, and Gary Hayward. The BP technical advisors/SCAT Coordinators included Ed Owens, Gary Mauseth, Andy Graham, Elliott Taylor, Greg Challenger, and Mike LaTorre. The BP SCAT data managers included Teresa Allard, Doug Reimer, and Alain Lamarche. All of them were key members of the SCAT Program and contributed to its success. BP SCAT team leaders and logistics personnel, state agency personnel from each state (LA, FL, AL, MS), and federal and state agency field representatives from USCG, NOAA, California Department of Fish and Game, other federal agencies, and federal contractors were all key members of the SCAT program.