Samples of contaminated concrete from the basement of the reactor building at Three Mile Island Unit 2 were tested and analyzed at Oak Ridge National Laboratory to determine the potential for decontamination by diffusion-controlled leaching under conditions of full submergence and by forced flow-through leaching of porous concrete block walls. Pertinent physical characteristics of the concrete were measured, and leaching tests were performed. Data were analyzed by established mass transport principles, and predictions of leaching for several years were made. A numerical algorithm was used to model removal of 137Cs and 90Sr by forced flow-through leaching. Results indicated that forced flow-through leaching would require only a few days, whereas complete decontamination by submerged, diffusion-only methods would require several years.