Modeling contaminant migration from a mixed-waste disposal site: Studies of controlling factors and processes

The Radioactive Waste Management Complex (RWMC) is located in the southwestern part of the Idaho National Engineering Laboratory in southeastern Idaho. Since the mid-1950s, the RWMC has served as a low-level and transuranic (TRU) waste disposal site. It is currently estimated that ∼180,000 m3 of solid waste has been buried at the site. Early modeling studies of contaminant migration concluded that it should take many thousands of years for contaminants to migrate any appreciable distance through the 580-ft fractured-basalt vadose zone. Recent field data from the site, however, show that both volatile organic chemicals and TRU elements have migrated a significant distance in the last 30 yr. Trace levels of volatile organic chemicals and TRU elements have migrated a significant distance in the last 30 yr. Trace levels of volatile organic chemicals (VOCs), such as carbon tetrachloride, chloroform, trichloroethylene, and tetrachloroethylene, have been detected in the groundwater, indicating an extensive movement of the vapor-phase component. Minute quantities (∼10-7 μCi/g) of plutonium and americium have been measured in core samples taken from a sedimentary interbed located ∼110 ft below the site. Computer modeling studies of the contaminant migration at the site are being performed to (a) develop an understanding of the processes and factors that have caused the migration and (b) to examine potential remedial actions. These studies are also aimed at addressing technical issues. Preliminary findings and selected simulation results are discussed in this paper