Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. AcknowledgementsThis work is supported wholly by the Department of Defense, through the Strategic Environmental Research and Development Program (SERDP). 1 Executive SummaryIn situ chemical oxidation (ISCO) using permanganate is an approach to organic contaminant remediation increasingly being applied at hazardous waste sites throughout the United States. Manganese dioxide (MnO 2 ) particles are products of the reaction of permanganate with organic contaminants and naturally-reduced subsurface materials. These particles are of interest because they have the potential to deposit in the subsurface and impact the flow regime in and around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. The goal of this research is to understand the genesis and control of MnO 2 particles and to identify particle stabilization aids that will allow for their transport in groundwater through porous media under a variety of reaction conditions. Control of these particles can allow for improved oxidant injection, oxidant transport, and contact between the oxidant and contaminants of concern. This project's specific objectives are to determine (1) if manganese dioxide particles can be stabilized/controlled in an aqueous phase to allow for transport through a solids phase, thereby inhibiting subsurface deposition, and (2) the dependence of stabilization and control of MnO 2 particles on porous media and groundwater characteristics. Bench-scale batch experiments to initially study important chemical interactions, followed by column studies to incorporate transport phenomena, were conducted to study particle stabilization aids under varied reaction matrix conditions. Variations include particle and stabilization aid concentrations, groundwater ionic content, pH, porous media type, and redox conditions. Four stabilization aids were evaluated in the batch experiments for their ability to stabilize particles in solution over time and a range of groundwater conditions. The stabilization aid sodium hexametaphosphate (HMP) demonstrated the most promising results based on:• Spectrophotometric studies of particle behavior • Particle filtration results at va...