SCAT Delineation of Oiling, Cleanup Verification, Chemical Sampling, Coring, and Mangrove Test Planting, Bodo, Eastern Niger Delta, Nigeria

Abstract

The Shoreline Cleanup Assessment Technique (SCAT) was effectively applied from 2015 to 2019 during the first stage (Phase 1) of assessment and cleanup of 1000 ha (2471 acres) of intertidal dead mangroves and oiled shorelines in Bodo, Eastern Niger Delta. New SCAT methods and Phase 1 cleanup criteria were developed to delineate oil levels very soft intertidal mud and to monitor clean up efforts. The end goal of Phase 1 was to reduce subsurface oiling less than 35% as visually observed on the water infilling a pit 25–40 cm deep. Oiling levels and cleanup status were documented at 1065 locations with heaviest oil concentrations found in soft muds lining the intertidal channels (2 m tide range). A large-scale chemical sampling program provided contemporaneous pit observations and measured hydrocarbons at 0–5 cm and 15–25 cm depths at 322 sites. There was poor conformance between hydrocarbon analyses and SCAT observations for surface sediments, but better conformance with subsurface chemistry as black and / or brown oil was clearly visible in the pits. Results of SCAT observations and chemical sampling show very high variations throughout the spill affected area and over short distances (5–10 m). A coring study at 30 sites to 2–3 m depths with chemical sampling indicated that oiling is primarily restricted to the upper 40 cm due to water saturated compact deeper sediments inhibiting oil penetration with depth. Lastly, SCAT developed and monitored a mangrove planting program. In spite of high oil levels (TPH over 40,000 at 6 of 7 sites), results from the first year show plant survival at 82% with 46% height growth of the surviving plants. The SCAT Phase 1 findings enabled the definition of the wider scope for remediation and revegetation of the former mangrove areas and will run through the life-cycle of the clean-up project. However, re-pollution remains a challenge to be managed to achieve success.