Design and Installation of a Permeable Treatment Wall to Passively Remove Strontium-90 From Groundwater at a Former Commercial Nuclear Fuel Reprocessing Facility in New York

A permeable treatment wall (PTW) was designed and installed at the West Valley Development Project (WVDP), a former commercial nuclear fuel reprocessing facility in New York, to passively remove and contain the expansion of strontium-90 (Sr-90) in the site groundwater. AMEC engineers and geologists have collaborated with researchers at the State University of New York at Buffalo (UB) and West Valley Environmental Services LLC to design and install an approximately 260 meter (860-foot) long by 0.9 meter (3-foot) thick zone of granular zeolite (a natural aggregate composed of approximately 85 percent of the mineral clinoptilolite) that will remove Sr-90 in situ from groundwater through ion-exchange reactions. The PTW was designed to meet the functional objectives for up to 20 years; performance monitoring will be conducted regularly and will be used to assess the lifetime efficacy of the PTW. The zeolite-filled PTW was the selected remedial alternative due to its hydraulically passive operations and lower life-cycle cost over other more traditional active treatment alternatives such as pump and treat. The design relied heavily on detailed site characterization of site soils and groundwater conditions and bench and pilot scale evaluations of various zeolite materials. The design specified the use of a one-pass trencher to simultaneously remove unconsolidated aquifer material composed of glaciofluvial-derived silt, sand, and gravel from ground surface to depths up to approximately 9 meters (30 feet) and replace the excavated zone with zeolite along the entire alignment while keying the PTW at least 0.9 meter (3 feet) into the underlying low-permeability glacial till. Several technology demonstrations were conducted to assess implementability using the one-pass trencher prior to completing the final design. During full-scale implementation, excavated sediment was conveyed directly into a prefabricated containment structure pending final disposition. The passive design provides a cost effective and sustainable alternative for treatment of Sr-90 and potentially other exchangeable radioactive ions in groundwater where these constituents migrate in unconsolidated materials.