A site specific treatability test was conducted to optimize polyphosphate remediation technology for implementation through a field-scale technology demonstration to accelerate monitored natural attenuation of the uranium plume within the Hanford 300 Area aquifer. A focused application of polyphosphate was conducted in a source or “hot spot” area to reduce the inventory of available uranium that contributes to the groundwater plume through direct precipitation of uranyl-phosphate solids and secondary containment via precipitation of apatite acting as a long-term sorbent for uranium. The general treatability testing approach consisted of initial site characterization and setup, a polyphosphate injection test, and post-treatment performance assessment. Fundamental science studies were conducted with site specific sediment and groundwater to develop an effective remediation scheme for deployment of polyphosphate technology. In addition to remediating a portion of the plume, the data from this test provides valuable information for designing a full-scale remediation of uranium in the aquifer at the 300 Area of the Hanford Site. It will also provide a detailed understanding of the fundamental underpinnings necessary to evaluate the efficacy and potential utilization of polyphosphate technology at other sites with varying geochemical and hydrodynamic conditions.