Digital Soil Core Reconstruction

research contact: Gerilynn Moline

Understanding the mechanisms controlling the transport of solutes and colloids is critical to designing monitoring and remediation strategies for subsurface contamination. In complex fractured porous media, geologic structure appears to play a key role in determining the direction and rate of transport as well as in controlling the rate of mass transfer between fractures and matrix pores. Multiple tracer techniques coupled with High-Resolution X-ray Computed Tomography are providing ORNL researchers new and important information about the relationships between geologic structure and contaminant transport processes.

Complex geology underlying the Oak Ridge Reservation

The complexity of geologic structures, such as these thinly-bedded heavily fractured soils underlying the Oak Ridge Reservation, presents a significant challenge for understanding and predicting the transport of contaminants through these materials.

Controlled transport experiments using undisturbed soil materials

ORNL researchers are conducting controlled transport experiments using undisturbed soil materials. Here, a suite of tracers is being injected through an undisturbed column that has been carefully carved out of a hillslope and encased in PVC pipe (located just right of the cinder blocks). The effluent is captured and analyzed for tracer concentrations.

CAT scans of soil columns conducted at UT-Austin's High Resolution CT laboratory

To determine the links between the fracture characteristics and transport behavior, CAT scans of soil columns are conducted at the University of Texas at Austin's High Resolution CT laboratory in order to image the internal structure of the columns. A bucket of sand (sitting on top of a column) is used to periodically check the instrument calibration.

CAT images representing density differences detected in slices through the column

CAT images represent density differences detected in slices through the column. The images are processed to remove artifacts, and colors are assigned to density ranges to enhance visualization. Here, the low-density pores and fractures are indicated in blue, high-density rock material is shown in red, and the intermediate colors represent moderately to highly-weathered rock material.

3D reconstruction of the column using CAT image data

CAT image data are combined to produce a 3D reconstruction of the column that can then be interrogated by slicing the grid in various orientations. In this 3D rendering using a different color scheme, the fractures can be clearly identified. These reconstructions provide critical information about the structure and characteristics of the primary contaminant transport pathways in these materials.