Predicting Soil Physical Parameters and Copper Transport in a Polluted Field From X Ray CT-Images.

The development of 3D imaging techniques provides non-destructive tools to reveal the soil structure. X-ray computed tomography (CT) analysis has succeeded in predicting pore network properties such as macropore size distribution, tortuosity, and hydraulic properties. Since contaminant transport in soils is strongly controlled by the soil structure, the capabilities of these visualization techniques could be used to predict the risk of pollutants leaching.

This work was carried out using soils from a field site (Hygum) in Jutland, Denmark, a historical copper (Cu) polluted field cultivated for 80 years and abandoned since 1993. Undisturbed soil cores were collected at 4 different locations along a gradient in Cu content (from about 20 to about 3800 mg Cu kg^-1 soil). Samples were scanned using X-ray CT. X-Ray CT macroporosity (cm³ cm^-3) was calculated as the ratio of the volume of pore voxels to the volume of each soil column. Leaching experiments were performed to analyze tritium transport, colloid leaching and dissolved organic carbon and Cu losses associated with particles or dissolved organic matter (DOM). Air permeability and saturated hydraulic conductivity were measured before and after the leaching experiments, respectively.

X-ray CT macroporosity satisfactory predicted air permeability and saturated hydraulic conductivity (R² > 0.72), as well as the transport parameters calculated from tracer breakthrough curves -5% tracer arrival time and apparent dispersivity (R² >0.87). Furthermore, the amount of DOM-Cu released during the leaching experiment was related with X-ray macroporosity (R²> 0.7). These preliminary results encourage us to examine other X-ray CT parameters like macropore length density, mean tortuosity, network density, path number, or node density, which should improve the models.