PERMEABLE TREATMENT WALL PILOT PROJECT AT THE WEST VALLEY DEMONSTRATION PROJECT

Treatment wall technology is increasingly being recognized as an effective means of mitigating groundwater contamination at sites worldwide. A pilot permeable treatment wall (PTW) project has been developed for mitigating strontium-90 (Sr-90) contaminated groundwater at the West Valley Demonstration Project (WVDP) in West Valley, New York. This PTW uses two technologies, ion exchange and in-situ treatment to remove Sr-90 as groundwater flows passively through the wall. Deployment of the pilot PTW project marks the culmination of a series of laboratory and bench-testing programs and conceptual design efforts. It also represents a collaborative effort among technical and scientific experts from industry, academia, the United States Department of Energy (DOE) and West Valley Nuclear Services (WVNS) to match an innovative technology with an existing remedial need. The key elements of the design process are summarized to indicate how the 9 meters long by 2 meters wide by 8.5 meters deep excavated area was selected as the most effective size, location, and configuration for the pilot PTW. Additionally, the methodology used to select clinoptilolite (CH 14 x 50), a natural inorganic zeolite, as the in-situ treatment media is presented. Results from bench testing at a variety of laboratories indicates the wall design to have an effective operating lifetime of more than 25 years. The assessment program for confirming wall performance during its operational phase is outlined, followed by a discussion of potential future uses of this type of PTW at other locations at the WVDP site. BACKGROUND AND HISTORY The West Valley Demonstration Project (WVDP) is located at the site of the only commercial spent nuclear fuel reprocessing plant ever operated in the United States. The North Plateau refers to a geographic area within the WVDP site that includes the former reprocessing plant building. From a geologic standpoint, the North Plateau contains an upper sand and gravel water bearing unit isolated by surrounding stream valleys. Groundwater seepage occurs on the face of the plateau as the topography drops off, and in low lying areas. A radioactive groundwater plume emanates from beneath the former reprocessing plant building in a northeasterly direction on the plateau. The sand and gravel unit is underlain by a clay-silt till that inhibits any downward contaminant migration. The extent of the plume is shown in Figure 1. The plume’s source has been traced to a leak in a process line that occurred during reprocessing operations (1968-1971), approximately ten years before the Department of Energy was authorized by Congress to begin the WVDP. Radioactive contamination from the leak has migrated very slowly in a northeasterly direction over the last 30 years. Extensive sampling and analysis identified strontium-90 (Sr-90) as the primary contaminant associated with the plume. The area of contamination southeast of the main body of the plume is associated with a former unlined retention basin.