2008 Annual Report 1a.Objectives (from AD-416) Perform coupled measurements of soil hydraulic properties and colloidal breakthrough in soil columns for the further interpretation of results using soil computer tomography data to quantify connectivity in soil macropores. 1b.Approach (from AD-416) Will measure soil water retention, soil hydraulic conductivity, bacteria or colloidal microsphere breakthrough, and conservative transport breakthrough in soil columns for which the computer tomography was performed. The research will be conducted in a phased approach according to the following three tasks. . 1)Measure hydraulic properties of the tomographed soil columns;. 2)Perform the column breakthrough experiments with bacteria or colloidal microspheres; and. 3)Schedule of the research and reporting. 3.Progress Report The research consisted of data collection and data analysis in order to relate soil hydraulic parameters to the structure of soil pore space which was earlier visualized and quantified using X-ray computer tomography. The prominent contribution of macropores to water flow and solute transport points to the need for thorough characterization of their void structure. Large soil columns need to be studied to infer topological properties of macropores. We have sampled and studied undisturbed columns (7.5 cm ID, 20 cm length) of the Taylor soil from a grassed floodplain in Franklin county, PA. The FlashCT - 420 kV system (HYTEC Inc.) was used for X-ray CT scanning. The high-connectivity macropore space was reconstructed from the imagery. The columns were first cut in half, then in four, and finally in eight equal parts. Saturated hydraulic conductivity increased with decrease in the column length. Pinched-out macropores within the column were found that affected the hydraulic conductivity of samples of different sizes. The overall large macroporosity did not translate into large hydraulic conductivity of the column. Introducing a novel parameter – the through macroporosity – appeared to be useful to quantify the observed effects. Soil water retention was measured at the smallest parts of the column for further modeling of capillary effects as related to macroporosity. The 3D CT scan data highlighted and eliminated substantial pitfalls in characterization of the soil void space structure that may arise from using of the 2D information about macroporosity. The progress of the work has been monitored by monthly teleconferences, two meetings with the Spanish counterparts, and weekly group meetings.