PNNL

Abstract

Efforts to reduce the flux of Sr-90 to the Columbia River from Hanford Site 100-N Area past-practice liquid waste disposal sites have been underway since the early 1990s. Termination of all liquid discharges to the ground in 1993 was a major step toward meeting this goal. However, Sr 90 adsorbed on aquifer solids beneath liquid waste disposal sites and extending beneath the near-shore riverbed remains a continuing contaminant source to groundwater and the Columbia River. The initial pump-and treat system proved to be ineffective as a long-term solution because of the geochemical characteristics of Sr-90. Following an evaluation of potential Sr-90 treatment technologies and their applicability under 100 NR-2 Operable Unit hydrogeologic conditions, the U.S. Department of Energy and the Washington State Department of Ecology agreed to evaluate apatite sequestration as the primary remedial technology, combined with a secondary polishing step utilizing phytoextraction if necessary. Aqueous injection was initiated in July 2005 to assess the efficacy of in-situ apatite along the 100 m of shoreline where Sr-90 concentrations are highest. The remedial technology is being developed by Pacific Northwest National Laboratory. CH2M Hill Plateau Remediation Company is implementing this technology in the field with support from PNNL.