Preferential Solute Flow in Intact Soil Columns Measured by SPECT Scanning

Single photon emission computed tomography (SPECT) is an imaging technique that is widely used in medical diagnosis. This technique has never been applied to soils. The objective of this study was to investigate the capabilities of SPECT scanning for visualizing preferential flow in soil. This paper describes the principle of SPECT scanning and its application to tracer breakthroughs in four large undisturbed soil columns (800‐mm length × 77‐mm diam.). This new approach allows real‐time analysis of flow patterns of radioactive tracers in 2‐D using planar imaging, and in 3‐D using the tomographic capabilities of the SPECT scanner. Not only does SPECT scanning provide qualitative data, but it also allows for the quantification of a tracer's spatial distribution. Our results characterized preferential flow very clearly in soil columns. SPECT scanning opens up new avenues for 2‐D and 3‐D tracer studies in porous media such as soils.