Despite remediation efforts, low concentrations of the chlorinated solvents 1,1-dichloroethane, 1,2-dichloroethane, and their additive, 1,4-dioxane (1,4-D), can persist within impacted groundwater. Common to these three chemicals are their capability to be oxidized into less toxic compounds, and consequently in situ chemical oxidation (ISCO) is a common remediation strategy, particularly that involving Fenton chemistry and reactive oxygen species (ROS) generation. To meet the need for creating more favorable and prevalent reactive conditions in the subsurface, the project team will explore whether Fenton chemistry can be modified to produce more ROS, particularly hydroxyl radicals, in a long-term, sustained manner. The objective of this research project is to evaluate the usefulness of a new solid catalyst, nanosized manganese dioxide (nMnO₂), in Fenton-like oxidation of the three persistent chemicals of concern in anticipation of expanding the possible applications of ISCO remediation methods.

The central hypothesis for this project is that nMnO₂ in combination with H₂O₂ can effectively degrade dissolved 1,1-dichloroethane, 1,2-dichloroethane, and 1,4-D within time frames comparable to, or faster than, conventional Fenton reaction. Laboratory experiments will be conducted to determine the efficacy and limitations of nMnO₂ to generate hydroxyl radicals and superoxide from activation of H₂O₂ under simulated conditions relevant to the subsurface. Likewise, the reactivity of the nMnO₂-H₂O₂ system to 1,1-dichloroethane, 1,2-dichloroethane, and 1,4-D will be evaluated under various geochemistry to identify suitable application conditions and any interferences. Kinetic studies will be used to describe key reactions and to compare to conventional oxidation technologies. Products of chemical degradation will be sought to understand chemical transformation pathways. Column studies will be performed to understand nanoparticle transport and reactivity in porous media. The ability to reuse the nMnO₂ catalysts will also be assessed.

This research will support remediation efforts for the more recalcitrant chemicals prevalent in chlorinated solvent and hydrocarbon groundwater plumes. Nanosized MnO₂ as an alternative solid-phase catalyst will provide new possibilities for activating hydrogen peroxide and ROS generation in ISCO strategies. The range of geochemical conditions for which nMnO₂ is effective for oxidation of 1,1-dichlorethane, 1,2-dichloroethane, and 1,4-D will be determined. Whether nMnO₂ is capable of furthering this reaction into less toxic products will be determined. A kinetic model describing the ROS generation and chemical degradation will be developed and will allow prediction of optimized in situ conditions for nMnO₂ and H₂O₂ deployment. Finally, how to best deploy MnO₂ into the subsurface, and for how long nMnO₂ reactivity can be maintained in situ will be explored. (Anticipated Project Completion - 2026)