Abstract
Trial pitting, borehole drilling, and soil, sediment and groundwater sampling are important components of oil spill response and contaminated land assessment. These investigations provide detailed information on the subsurface geology and contaminant occurrence and transport but have disadvantages including worker safety hazards, cost and time required for completion, and may cause cross-contamination among aquifers. An alternative to such investigations applied in oil spill response is the Shoreline Cleanup Assessment Technique (SCAT) approach, which relies heavily on direct visual observations to assess the severity of oil contamination and guide cleanup efforts. Here, we compare SCAT observations of oil type, surface coverage and pit oiling with collected surface and subsurface sediment samples taken concurrently and analysed for a suite of hydrocarbon constituents. Results indicate that although limited sampling and analysis is required to chemically characterize the contamination, SCAT observations can be calibrated using limited sediment sampling and are sufficient to steer physical cleanup methods. This is particularly evident as even closely spaced chemical samples show high variability. A coarser direct visual observation is fit-for-purpose considering the wide variability in contaminant distribution at even local levels. In this contribution, we discuss the limitations of the different methods. Supplementary material: The modified SCAT data collection form, figures showing subsurface versus ground surface total petroleum hydrocarbons (TPH) and a variogram of TPH measured in the ground surface and subsurface samples, and data tables are available at https://doi.org/10.6084/m9.figshare.c.4534682 Thematic collection: This article is part of the Measurement and monitoring collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring
Highlights
It is interesting to note that subsurface sediment concentrations are consistently lower than surface concentrations, the correlation between surface and subsurface collected at the same location is very poor (R2 = 0.12; Fig. SI-1 in supplementary material), highlighting the high degree of heterogeneity
The results of vibracoring and analyses undertaken in September–October 2018 at depths of 2–4 m reveal that the vast majority of petroleum hydrocarbon impact is restricted to depths of
The relative standard deviation (RSD) of total petroleum hydrocarbons (TPH) in the classes for the subsurface shown in Figure 11 range between 115% for black oil and 219% for silver sheen (Table SI-1 in supplementary material), which is higher than that of the small-scale sampling discussed in the previous section (33–96%)
Summary
Sediment sampling for chemical analyses was carried out before, during and after the first phase of cleanup in conjunction with the abovedescribed SCAT site investigations. We utilize data from 317 SCAT sites that have observations of surface and subsurface oiling and results from chemical analysis.
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