A radioactive waste excavation at Mound Area 7 using INEL dig-face monitoring technology

Dig-face characterization is a method to improve the safety and efficiency during hazardous waste retrieval. A dig-face characterization system consists of on-site hardware for collecting detailed information on the changing chemical, radiological, and physical conditions in the subsurface throughout a hazardous site excavation. The dig-face characterization concept originated at the Idaho National Engineering Laboratory where it has been under development since 1992. In August 1995, a prototype dig-face system was taken to Mound Laboratory, Ohio, to monitor a hazardous waste site excavation. Mound Area 7 was the site of previous disposal of 232Th, 227Ac, and other waste. The dig-face characterization system was used to monitor a 20-ft x 20-ft x 5-ft-deep excavation intended to remove the 227Ac contaminated soils. Radiological, geophysical, and topographical sensors were scanned across each of four successive excavated soil levels, each 1-ft to 2-ft thick. The radiation sensors produced highly detailed images showing the location of the contaminants 232Th and 227Ac, and the clear delineation between them. When combined into a single data set, the four levels of collected data produced a three dimensional image of the contamination. The radiation sensor data indicated that only a small portion of the excavated soil was actually contaminated. The information produced by the dig-face system was used to direct precise excavation activities in the area containing the 227Ac and to plan subsequent removal of the separate 232Th plume