Column-Test Data Analyses and Geochemical Modeling to Determine Uranium Reactive Transport Parameters at a Former Uranium Mill Site (Grand Junction, Colorado)

The long-term release of uranium from residual sources at former mill sites was often not considered in prior conceptual and numerical models, as contaminant removal focused on meeting radiological standards. To determine the reactive transport parameters, column tests were completed with various influent waters (deionized water, site groundwater, local river water) sediment identified areas elevated solid phase (1) vadose-zone (VZ) sediments, (2) saturated-zone sediments higher organic carbon content, (3) both vadose- additional gypsum content. precipitated when low-pH, high-sulfate, tailings fluids or acidic waste disposal water buffered by natural aquifer calcite dissolution. In general, resulting greater concentrations. However, addition deionized (DI) to VZ delayed until higher-alkalinity groundwater added. Higher-alkalinity continued remove for an extended number pore volumes, being above typical Thus, flooding is more efficient removing than precipitation events (DI tests). Organic provides a stronger sorption surface, which can be explained geochemical modeling larger constant coefficient (Kd). Without carbon, sands gravels easily measurable, but lower, water-phase This effect simulated modeling, Kd. Areas create situations difficult simulate, likely due presence within mineral coatings. All mechanisms must evaluating remedial strategies. Column testing initial input parameters that used future evaluate rates