PNNL

Currently, there are large dilute 129I groundwater plumes at Hanford, including a groundwater plume in the 200-UP-1 operable unit (OU) located within the Central Plateau of the Hanford Site. The interim record of decision for the 200-UP-1 OU requires that the U.S. Department of Energy evaluate potential treatment options for 129I through further technology evaluation. The approach to the evaluation was defined in the 129I technology evaluation plan and includes an update to the conceptual model (CM) for the plume, as required by the 200 UP 1 remedial design/remedial action work plan. This report describes an updated CM of subsurface processes that affect 129I behavior in the subsurface. This CM was developed to address identified data gaps and to provide input for fate and transport modeling needed to support the remedy evaluation. A significant advancement from previous the CM for the 200-UP-1 OU is recognition of the multiple iodine species in the subsurface and the biogeochemical processes that control their fate and transport.