Non-destructive Analysis of Oil-Contaminated Soil Core Samples by X-ray Computed Tomography and Low-Field Nuclear Magnetic Resonance Relaxometry: a Case Study

Abstract

Non-destructive measurements of contaminated soil core samples are desirable prior to destructive measurements because they allow obtaining gross information from the core samples without touching harmful chemical species. Medical X-ray computed tomography (CT) and time-domain low-field nuclear magnetic resonance (NMR) relaxometry were applied to non-destructive measurements of sandy soil core samples from a real site contaminated with heavy oil. The medical CT visualized the spatial distribution of the bulk density averaged over the voxel of 0.31 × 0.31 × 2 mm3. The obtained CT images clearly showed an increase in the bulk density with increasing depth. Coupled analysis with in situ time-domain reflectometry logging suggests that this increase is derived from an increase in the water volume fraction of soils with depth (i.e., unsaturated to saturated transition). This was confirmed by supplementary analysis using high-resolution micro-focus X-ray CT at a resolution of ∼10 μm, which directly imaged the increase in pore water with depth. NMR transverse relaxation waveforms of protons were acquired non-destructively at 2.7 MHz by the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence. The nature of viscous petroleum molecules having short transverse relaxation times (T2) compared to water molecules enabled us to distinguish the water-saturated portion from the oil-contaminated portion in the core sample using an M0–T2 plot, where M0 is the initial amplitude of the CPMG signal. The present study demonstrates that non-destructive core measurements by medical X-ray CT and low-field NMR provide information on the groundwater saturation level and oil-contaminated intervals, which is useful for constructing an adequate plan for subsequent destructive laboratory measurements of cores.

Micro-scale determinants of bacterial diversity in soil

“…This method has been for instance used to locate the presence of heavy oil contamination in a soil core (in conjunction with lCT) (Nakashima et al, 2011). water).…”

“…water). This method has been for instance used to locate the presence of heavy oil contamination in a soil core (in conjunction with lCT) (Nakashima et al, 2011). It has the potential to locate nuclei that 'spin', which include 1 H, 2 H, 13 C, 14 N, 15 N, and 31 P (Haynes, 2012).…”

The use of sodium polytungstate as an X-ray contrast agent to reduce the beam hardening artifact in hydrological laboratory experiments

“…The experimentally measured bulk density of the KI 9.16 wt.% solution was 1.07 g/cm 3 (Nakashima, 2000), and that of the SPT 8.80 wt.% solution was 1.08 g/cm 3 . The samples were imaged by a third-generation medical CT scanner (W2000, Hitachi Medical Co., Tokyo, Japan) at the Geological Survey of Japan (Nakashima, 2000;Nakashima, 2003;Nakashima and Nakano, 2012;Nakashima et al, 2011) to obtain two-dimensional (2-D) 16-bit TIFF CT images. The imaging conditions were as follows: acceleration voltage, 130 kV; tube current, 100 to 175 mA; slice thickness, 5 mm; field of view of the reconstructed 2-D image, 160 2 mm 2 = 512 2 voxels (three-dimensional voxel dimension, 0.31×0.31×5 mm 3 ); X-ray exposure time, 4 s; reconstruction filter, Chesler type (standard filter for the human abdomen).…”

Soil Aggregate Microbial Communities: Towards Understanding Microbiome Interactions at Biologically Relevant Scales

“…Scanning electron microscopy (SEM) and microcomputed tomography (CT) use electrons and X rays, respectively, to visualize soil structures and cells with nanometer-to micrometer-scale resolution (91,92). Nuclear magnetic resonance (NMR) nondestructively locates hydrogen nuclei, providing information about water and hydrocarbon distributions among aggregates (93). Infrared spectroscopy and nanoscale secondary ion mass spectrometry (Nano-SIMS) yield information about micrometer-scale identity, location, and quantification of elements and minerals in soils, including intact aggregates (94)(95)(96)(97).…”