Three-dimensional visualization and quantification of non-aqueous phase liquid volumes in natural porous media using a medical X-ray Computed Tomography scanner

• Published in: Journal of contaminant hydrology Vol. 93; no. 1; pp. 96 - 110
• Main Authors: Goldstein, Lucas, Prasher, Shiv O., Ghoshal, Subhasis
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.08.2007; Elsevier Science
• Subjects: computed tomography; Computer Simulation; Crystallography, X-Ray - methods; Earth sciences; Earth, ocean, space; Equipment Design; Exact sciences and technology; Gasoline; groundwater contamination; Hydrogeology; Hydrology. Hydrogeology; Imaging, Three-Dimensional; Models, Statistical; Non-aqueous phase liquids; Non-destructive imaging; nonaqueous phase liquids; Porosity; porous media; sand; Silicon Dioxide; Software; Soil; spatial distribution; Tetrachloroethene; tetrachloroethylene; Tetrachloroethylene - chemistry; Tomography, X-Ray Computed - methods; Water Movements; Water Pollutants - chemistry; X-ray Computed Tomography; X-Rays; Non-destructive imaging; Tetrachloroethene; X-ray Computed Tomography; Non-aqueous phase liquids; Gasoline; nonaqueous phase liquids; accumulation; liquid phase; porosity; X-rays; spatial distribution; grains; saturation; sand; instruments; positioning; tomography; noise; soils; porous media; errors
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/j.jconhyd.2007.01.013

This study demonstrates the capabilities of a typical medical X-ray Computed Tomography (CT) scanner to non-destructively quantify non-aqueous phase liquid (NAPL) volumes, saturation levels, and three-dimensional spatial distributions in packed soil columns. Columns packed with homogeneous sand, heterogeneous sand, or natural soil, were saturated with water and injected with known quantities of gasoline or tetrachloroethene and scanned. A methodology based on image subtraction was implemented for computing soil porosity and NAPL volumes in each 0.35 mm × 0.35 mm × 1 mm voxel of the columns. Elimination of sample positioning errors and instrument drift artifacts was essential for obtaining reliable estimates of above parameters. The CT data-derived total NAPL volume was in agreement with the measured NAPL volumes injected into the columns. CT data-derived NAPL volume is subject to a 2.6% error for PCE and a 15.5% error for gasoline, at average NAPL saturations as low as 5%, and is mainly due to instrument noise. Non-uniform distributions of NAPL due to preferential flow, and accumulation of NAPL above finer-grained layers could be observed from the data on 3-D distributions of NAPL volume fractions.