Reactant Carrier Microfoam Technology for In-Situ Remediation of Radionuclide and Metallic Contaminants in Deep Vadose Zone

The U.S. Department of Energy (DOE) is currently developing advanced remedial technologies for addressing metal and radionuclide (Cr, Tc, and U) contamination in deep vadose zone environments. One of the transformational technology alternatives being considered by the DOE Office of Environmental Management, is the use of Reactant Carrier Microfoams (RCM) as a minimally invasive method for delivery and emplacement of reagents for in-situ immobilization of contaminants. Penetration of low permeability zones deep within the subsurface for Enhance Oil Recovery (EOR) has been well-established. Use of surfactant foams have also been explored for mobilizing DNAPL from sediments. So far, the concept of using RCM for immobilizing labile metal and long-lived radionuclide contaminants in the deep vadose zone has not been explored. We, at the Pacific Northwest National Laboratory (PNNL), conducted studies to develop stable foams as a means to deliver reductive and/or precipitating reactants to the deep subsurface. To test the feasibility of this approach, we developed a preliminary foam formulation consisting of a mixture of an anionic and a nonionic surfactant with a reactant consisting of a 9:1 blend of tripoly- and orthophosphate. The MSE Technology Applications, Inc (MSE) in collaboration with PNNL, conducted a scale-up test to evaluate themore » efficacy of this reactant carrier foam for in-situ immobilization of U containing sediment zones in a heterogenous sediment matrix. The data indicated that successful immobilization of U contamination is feasible using specifically tailored reactant carrier foam injection technology. Studies are continuing for developing more robust optimized RCM for highly mobile contaminants such as Cr (VI), Tc (VII) in the deep vadose zone.« less