Quarterly Journal of Engineering Geology and Hydrogeology Comparison of chemical sediment analyses and field oiling observations from the Shoreline Cleanup Assessment Technique (SCAT) in heavily oiled areas of former mangrove in Bodo, eastern Niger Delta by Matthijs Bonte, Erich R. Gundlach, Ogonnaya Iroakasi, Kabari Visigah, Ferdinand Giadom, Philip Shekwolo, Vincent Nwabueze, Mike Cowing, and Nenibarini Zabbey Quarterly Journal of Engineering Geology and Hydrogeology Volume ():qjegh2019-018 July 23, 2019 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Location of the Bodo Creek study area along the eastern edge of the Niger River delta in Rivers State, Nigeria. Location of the Bodo Creek study area along the eastern edge of the Niger River delta in Rivers State, Nigeria. Background satellite image is copyright Google, image Landsat/Copernicus. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Overview of the central portion of the Bodo Creek study area showing living and dead (former) mangrove area. Overview of the central portion of the Bodo Creek study area showing living and dead (former) mangrove area. (a) photograph taken on 15 September 2015 (V. Imevbore photographer); (b) Google Earth image dated 2 January 2018. The location of the photograph is shown in Figure 4. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Overview of SCAT observations at sites L10-1 (top) and I49-1 (bottom) with pits, SCAT surface and subsurface oiling observations, and surface and subsurface TPH (mg kg−1). Overview of SCAT observations at sites L10-1 (top) and I49-1 (bottom) with pits, SCAT surface and subsurface oiling observations, and surface and subsurface TPH (mg kg−1). BO + BRO indicates black oil + brown oil. The locations of the sites are shown in Figure 4. Photographs by E. Gundlach. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Phase 1 work area outline in yellow with grids, former mangrove, live mangrove, water and illegal refineries indicated. Phase 1 work area outline in yellow with grids, former mangrove, live mangrove, water and illegal refineries indicated. The yellow arrow indicates location of the photograph in Figure 2. The location of the ‘Spills 2008’ that initiated these cleanup and sampling activities is also shown. The labels on the x- and y-axes of the map represent geographical coordinates (latitude and longitude) in decimal degrees. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Sampling locations (n = 317) with colours indicating TPH concentrations for surface (downward pointing triangle) and subsurface (upward pointing triangle) concentrations. Sampling locations (n = 317) with colours indicating TPH concentrations for surface (downward pointing triangle) and subsurface (upward pointing triangle) concentrations. The labels on the x- and y-axes of the map represent geographical coordinates (latitude and longitude) in decimal degrees. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Photographs showing sampling in grid cell P09 (4. 62582N, 7 Photographs showing sampling in grid cell P09 (4.62582N, 7.26295E) near a live mangrove. Photographs showing sampling in grid cell P09 (4.62582N, 7.26295E) near a live mangrove. (a) Collection of field grab samples using a steel shovel; these samples are composited in a stainless-steel bowl and homogenized. (b) Close-up of the pit (c. 0.3 m across) showing droplets of oil. (c) Homogenization of grab samples. (d) Transfer of composite sample to laboratory supplied sample containers, which were subsequently transferred to ice boxes and transported to the laboratory. Photographs by M. Bonte. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Box–whisker plots of TPH concentrations (in mg kg−1; log scale) for surface (G) and subsurface (S) samples under four different conditions: No Treatment, Pre-Treatment, During Treatment and Post-Treatment. Box–whisker plots of TPH concentrations (in mg kg−1; log scale) for surface (G) and subsurface (S) samples under four different conditions: No Treatment, Pre-Treatment, During Treatment and Post-Treatment. The number above the top x-axis represents the number of samples in each class. The box extends from the lower to upper quartile values of the data, with an orange line at the median (or 50%-ile). The whiskers extend from the box to show the range of the data between the 5- and 95%-ile. The green triangle shows the mean value. Flier points are those past the end of the whiskers. An asterisk above a box plot indicates that the median is significantly different at a 99% confidence level (P < 0.01) from the Pre-Treatment value. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

TPH fraction distribution for fresh Bonny Light crude oil and ground surface and subsurface sediment samples, before and after cleanup. TPH fraction distribution for fresh Bonny Light crude oil and ground surface and subsurface sediment samples, before and after cleanup. Ali, aliphatics; Aro, aromatics. Bonny #1 shows crude oil fractions from Brown et al (2017b). G, surface samples; S, subsurface samples; PreT, Pre-Treatment conditions; PostT, Post-Treatment conditions. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Results from blind duplicate sampling and analysis (n = 28). Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

TPH (in mg kg−1) from five discrete samples taken within 5 m of a central point at each site. TPH (in mg kg−1) from five discrete samples taken within 5 m of a central point at each site. Grey bars show TPH, the red line shows the mean of the five discrete samples and the green line shows the composite sample result from the same site. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Box–whisker plots of TPH concentrations (in mg kg−1; log scale) for different oil types as delineated by SCAT surveys for surface and subsurface samples. Box–whisker plots of TPH concentrations (in mg kg−1; log scale) for different oil types as delineated by SCAT surveys for surface and subsurface samples. The box extends from the lower to upper quartile values of the data, with an orange line at the median (or 50%-ile). The whiskers extend from the box to show the range of the data between the 5- and 95%-ile. Flier points are those past the end of the whiskers. The number above the upper x-axis indicates the number of samples in each group. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London

Box–whisker plots of TPH concentrations (in mg kg−1; log scale) of Post-Treatment samples for different types of SCAT surface and subsurface oil observations classified according to a proposed close-out criterion for Phase 2 under which SS plus BO ≤25%. Box–whisker plots of TPH concentrations (in mg kg−1; log scale) of Post-Treatment samples for different types of SCAT surface and subsurface oil observations classified according to a proposed close-out criterion for Phase 2 under which SS plus BO ≤25%. SS, silver sheen; BO, black oil; BRO, brown oil. Matthijs Bonte et al. Quarterly Journal of Engineering Geology and Hydrogeology 2019;qjegh2019-018 © 2019 Shell Global Solutions International BV. Published by The Geological Society of London