The March 1979 accident at Three Mile Island Unit 2 released reactor coolant and core material particles to the reactor building basement and by various side streams to the auxiliary and fuel-handling building systems. Consequently, existing plant materials and incidental debris became radioactively contaminated from contact with the primary coolant discharge. Additionally, the makeup and purification (MUP) system demineralizer resins were degraded by exposure to thousands of curies of iodine and cesium trapped in the vessels. Area radiation levels, ranging from ten to thousands of roentgens per hour, prevented or severely restricted access to these areas and prohibited local decontamination methods. To decontaminate these areas, several alternative methods were evaluated, and one was selected as the most economically acceptable and plant-compatible method to remotely collect, process, and dispose of these radioactive materials and degraded resins. The decision was made to modify the two 14.38-kl (3800-gal) in-plant spent-resin storage tanks (SRSTs) to operate as particulate separators by a decantation process. The level of particulate concentration by this process was determined by the physical and radiochemical characteristics of the materials, relative to the subsequent requirements for solidification and disposal operations. Various modifications and features were added to each SRST to allow them to operate as clarifiers for concentrating sediments as well as resins. The sequence of operation is to pump a batch of solids entrained in water to a tank, allow it to settle, decant the supernatant, repeat this process until sufficient solids are collected, and then pump the solids to a solidification disposal container. The first two waste streams processed by the SRSTs were the containment basement sediment and contaminated resins from the cleanup demineralizers. A campaign is currently in progress to remove the contaminated resins from the MUP demineralizers.