The objective of this study is to investigate the mobility of uranium after reaction of contaminated sediments with phosphate solutions injected at the 300 Area. Boreholes samples that were collected after phosphate injections will be subject of leaching studies that include i) semi-selective sequential uranium extractions, ii) extraction of labile uranium iii) and flow-through columns with field size and <2mm size fraction. The solid phases will be investigated using microscopic and spectroscopic methods to identify uranium mineral phase(s) and surface coatings prior and after sample extractions. Solids will be examined using Electron Microprobe (EMP), Scanning Electron Microscope equipped with Energy Dispersive Spectroscopy (SEM/EDS), and cryogenic time-resolved laser induced U(VI) fluorescence spectroscopy (TRLIFS) for characterization of mineral phases. Outmost interest will be given to identification of uranium species that are resistant to leaching treatments. The uranium leachability data from the post-treatment borehole samples will be compared with the pre-treatment information to evaluate and refine the remediation design for enhanced attenuation of uranium.