System-Scale Model of Aquifer, Vadose Zone, and River Interactions for the Hanford 300 Area – Application to Uranium Reactive Transport

This report represents a synthesis and integration of basic and applied research into a system-scale model of the Hanford 300 Area groundwater uranium plume, supported by the U.S. Department of Energy (DOE) Richland Operations Office (RL). The objective was to develop a three-dimensional model addressing water flow and reactive transport of uranium in the coupled vadose zone, unconfined aquifer, and Columbia River shoreline. Utilizing data from various DOE projects, the methodology involved integrating research findings to create a decision-support tool capable of evaluating processes affecting the groundwater uranium plume. Results indicated the model's effectiveness in simulating scenarios such as different remediation endpoints and field remediation strategies, including removal and treatment of contaminated sediments and monitoring of groundwater. Illustrative simulations of polyphosphate infiltration demonstrated the model's ability to address remediation questions. The application of this system-scale model, in conjunction with continued field monitoring, is expected to provide a rigorous basis for developing operational strategies for managing uranium contamination in the Hanford 300 Area.