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

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.