Transfer of mass between macropores and the soil matrix is an important control on flow and solute transport in the vadose zone. Few empirical techniques are available to explicitly investigate how the fast flows in macropores interact with the slower flows in the matrix to allow the flow system to evolve over time. In this study, time-lapse X-ray Computed Tomography (CT) scans are used to obtain quantitative 4D (i.e., transient three-dimensional) images of infiltration in two soil columns: one homogenous, non-macroporous and one containing a network of desiccation cracks. Water was applied to the top of each column at increasing rates over the flow period. High resolution (80 micron) CT images of the columns were collected throughout the infiltration experiments at 7-minute intervals. These images were processed to obtain time-varying maps of water content that provide insights to the evolution of the flow patterns and mechanisms of interaction between the macropore and matrix domains. Flow in the non-macroporous column was observed to be nearly uniform, whereas flow behavior in the macroporous column was dependent on the influent water flux. At low infiltration rates, film flow occurred in the macropores with comparatively little imbibition from macropore to matrix. At high infiltration rates, the macropores filled with water and imbibition to the matrix increased. Results demonstrate that wetting of the soil is a complex process reflecting contributions from downward infiltration through macropore-matrix networks and lateral wetting from the macropores.

Storing and recovering water, carbon and heat from geologic reservoirs is central to managing resources in a changing climate. We tested the hypothesis that the strain tensor caused by injecting or producing fluids can be measured at shallow depths and interpreted to advance understanding of underlying aquifers or reservoirs. Geodetic-grade strainmeters were deployed at 30m depth overlying the Bartlesville Formation, a 500-m-deep sandstone near Tulsa, OK. The strainmeters are 220m east of injection well 9A completed in a permeable lens at the base of the Bartlesville Formation. Water was injected into well 9A at approximately 1.0 L/s during four tests that ranged in duration from a few hours to a few weeks. The horizontal strain increased (tension) and the circumferential strain was a few times larger than the radial strain. The vertical strain decreased (compression) during injection. Strain rates were approximately 100 n/day during the first few hours, but the rates decreased and were approximately 10 n/day during most of the tests. Four independent methods of poroelastic simulation and inversion predict reservoir properties and geometries that are similar to each other and consistent with independent information about the reservoir. All strain interpretations predict that a boundary to the permeable lens occurs beneath the vicinity of the AVN strainmeters, which is consistent with core data from the site. The boundary of the permeable lens is located by matching the radial and circumferential strains, which demonstrates the value of measuring the strain tensor.