Tidal Flat and Sand Beach Remediation: Choosing Remediation Techniques to Speed Ecological Recovery of Habitats Still Impacted 20 Years after the Gulf War Oil Spill

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ABSTRACT After nearly 20 years of limited natural recovery following the Gulf War oil spill, surveys were conducted in 2009-2010 to identify where oil has persisted and ecological recovery has been slow along the Arabian Gulf coastline of Saudi Arabia. In 2011-2013, large-scale remediation projects were executed on 3 locations totaling 155 hectares of tidal flats and sand beaches to speed ecological recovery. Targeted remediation techniques were used as tools to meet the following goals: 1) increase suitable habitat for grazers and burrowing infauna; 2) reduce total petroleum hydrocarbon levels; and 3) improve physical processes (drainage) and reduce associated stressors such as ponding. Three principal techniques were developed and utilized along sheltered and moderately exposed tidal flats: 1) tilling of oiled sediments using tines (rake) or disc harrow attachment, followed by manual removal of remaining surface oil; 2) complete physical removal and disposal of the surface or cohesive subsurface oiling layers; and 3) tilling areas contained within berms while flooded to liberate liquid oil that was subsequently recovered by skimming/vacuuming. The first technique was considered appropriate when there was a well-defined gradient between hardened surface oiling and lightly oiled subsurface sediments, within sandy tidal flats, and where sediment conservation was a priority. This technique resulted in 20% additional oiled surface residue cover, which was removed manually. Resulting sediment loss was minimal. Goals 1, 2 and 3 were met. The second technique was preferred when there was a dry cohesive oiled layer either on the surface or beneath a layer of clean sand and where sediment conservation was not a priority. Excavation of oiled sediments resulted in high sediment loss by physical removal; however, goals 1 and 2 were clearly achieved. Additional re-grading including possible sediment replacement was required to achieve goal 3. The third technique was considered the optimal method when there was a high level of subsurface liquid oiling within tidal flats, and if sediment conservation was a priority. Goal 1 was achieved by breaking up surface barriers. To achieve goals 2 and 3, multiple tilling passes were required to liberate and remove liquid oil. Monitoring results show that while oil levels varied across remediated sites, a trend in reduction was common throughout. Short- and long-term ecological responses are being monitored.