[en] Water transport through welded tuff was studied with the aid of three drying experiments and one imbibition experiment performed on a single 0.15-m-long core. The specimen was saturated using a novel technique which measures the volume of water imbibed as a function of time in order to insure complete saturation. Profiles of saturation vs axial position along the core were provided by measuring the intensity of a beam of 662 keV gamma ray photons after passing through the sample in a direction normal to the axis of the cylinder. Measurements were made at different axial locations by moving the sample chamber past the beam with a precision translation table. Results indicate that the drying process is, in general, not characterized by a receding evaporation front as has been previously assumed, but rather by evaporation throughout the sample. Water appears to move through the sample under the action of both capillary forces and vapor pressure gradients induced by temperature gradients. Profiles resembling those of a receding evaporation front were observed when the temperature gradient was aligned in the direction of moisture transport. This work was performed in support of the Nevada Nulcear Waste Storage Investigation Project, which is responsible for examining the feasibility of siting a repository for commercial high-level nuclear wastes at Yucca Mountain and adjacent to the Nevada Test Site. 11 references, 9 figures